UNLV scientists back DOE on Yucca safety

Tuesday, Nov. 14, 2000 | 11:34 a.m.

RENO -- No deep, hot water has reached a potential high-level radioactive dumpsite at Yucca Mountain in the past 2 million years, a UNLV study released today says.

The conclusion, reached by UNLV researchers Jean Cline and Nicholas Wilson, supports claims by the U.S. Department of Energy and the U.S. Geological Survey that the site, 90 miles northwest of Las Vegas, is a place dry enough to bury 77,000 tons of spent nuclear reactor fuel and defense wastes.

The findings released at the Geological Society of America meeting today through Thursday deal a scientific blow to the state's argument that superheated water has invaded the repository site in recent geological history.

The UNLV research team for the first time has dated layers of minerals indicating that no such water has invaded the repository site in at least the past 2 million years. The evidence is "unquestionable," Cline said.

In fact super-hot water -- 300 degrees Fahrenheit or hotter -- could have entered Yucca's rock at the repository level as long ago as 5 million years or more based on the mineral evidence, Wilson said.

A congressional mandate in 1987 required scientists to prove whether or not deep, hot water had entered the area in the past 1.5 million years.

A leak of geothermal water into a high-level nuclear waste site could corrode the containers holding the waste and release dangerous levels of radioactivity.

If such a hydrothermal event had happened in the recent past, it could have stopped the nuclear industry from burying its waste at Yucca.

Cline and Wilson had to answer the crucial questions of if and when hot, deep fluid had moved through Yucca's younger volcanic ash layers to settle a 17-year-old scientific argument.

By taking rock samples every 150 to 215 feet, they gathered enough data to put the pieces of the geological puzzle together.

The key was analyzing a variety of mineral samples. Wilson had collected 155 rock samples from Yucca's 5-mile-long exploratory tunnel to observe the pattern of minerals deposited there over eons. Then he began probing the minerals with the latest instruments.

Wilson and Cline were able to date minerals in 16 samples of rock from Yucca and found no evidence of hydrothermal activity.

However, they did find evidence of possible hydrothermal activity 4 million to 5 million years ago. Some double bubbles, called two-phased fluid inclusions, were found in the oldest mineral layers, Wilson said. The two-phased fluid inclusions are generally formed in very hot water, above 300 degrees Fahrenheit.

Fluid inclusions are tiny bubbles of gas and water trapped in the minerals.

"We had hoped to answer some of the questions we had at the beginning," lead UNLV scientist Cline said of work done with $1.4 million in DOE funds. "We have quite solidly answered all of the questions."

Those questions were raised by former Department of Energy geologist Jerry Szymanski, who said in 1983 that deep, hot water periodically intruded into the repository site 1,000 feet beneath the surface of Yucca Mountain.

Cline and Wilson plan to publish their final results in April, after more rock samples are dated.

UNLV, the U.S. Geological Survey, DOE, the independent Nuclear Waste Technical Review Board and the state of Nevada all contributed scientific information to the study, and all were given oversight of Cline and Wilson's work.

Nevada officials, who are opposed to a nuclear repository, said after hearing the results that they still believe that geothermal water entered the mountain in recent geological history.

They also said that earthquakes or volcanic activity could disrupt the site, breaking open buried casks filled with deadly radioactive waste and allowing the hazardous waste to escape.

Russian scientist Yuri Dublyansky, a consultant for the state, was to present findings today that claim that geothermal water flowed into the mountain's dry tuff and formed fluid inclusions.

The U.S. Geological Survey suspected that hot, deep water had not risen inside Yucca, USGS project manager Zell Peterman said.

"I'm not expecting any surprises," Peterman said of the study's conclusions. "The UNLV and the USGS work meshes very well."

While the latest study doesn't help the state's argument that Yucca Mountain is flawed, Nevada Agency for Nuclear Projects Director Bob Loux said the battle to prevent burial of the highly radioactive waste there will continue.

There are other scientific issues under investigation that may raise serious questions about the mountain's stability, Loux said.

The Nuclear Regulatory Commission must license the site and is conducting its own research.