Russian scientist says Yucca site flooded thousands of years ago

Wednesday, June 2, 1999 | 11:30 a.m.

Ground water flooded the proposed Yucca Mountain nuclear waste site thousands of years ago, a Russian geologist said Tuesday, raising doubts about the project's safety.

The Department of Energy and the U.S. Geological Survey are designing a repository to seal off highly radioactive wastes underground for a minimum of 10,000 years, when the nuclear materials decay to safer levels.

But geologist Yuri Dublyansky of the Russian Academy of Sciences said that the flooding problem he found may be a "potential show-stopper." Dublyansky is a consultant for the state of Nevada, which opposes the Yucca Mountain repository site 90 miles northwest of Las Vegas.

Meanwhile, government scientists contradicted Dublyansky and said Tuesday there is no evidence of flooding or seepage of water that would threaten the integrity of the Yucca repository.

Dublyansky said that the finding could stop the high-level nuclear waste project that has been under study at Yucca Mountain by the two federal agencies for 15 years.

When the flooding occurred, calcite mineral crystals formed beneath the mountain. Bubbles that trapped gas and liquid in the minerals indicate the surrounding temperature was about 170 degrees, Dublyansky said.

Only deep ground water heated by the interior of the Earth could reach such a temperature, Dublyansky told the American Geophysical Union meeting in Boston this week.

Dublyansky said he does not know when the flooding occurred, but the youngest mineral deposits he discovered were a few hundred thousand years old.

The question of when the minerals were deposited is under study by a team of scientists at UNLV.

USGS scientists contradicted Dublyansky's studies, saying the water trickled into the mountain from rainwater at the surface.

The slow growth of calcite and opal, both minerals that coat fractures and cavities at Yucca Mountain, show that hot, deep water has not risen within the mountain for the past several million years, USGS scientists said.

"There is no evidence at Yucca Mountain, based on the distribution of calcite and opal, that water has ever flooded the potential repository area," James Paces, a USGS scientist from Denver, said.

Paces described the cavities in the mountain as being "relatively free" of deposits of calcite and opal. The deposits have been discovered at lower levels inside the cavities, he said, not on the ceilings. If ground water had flooded the site, the ceilings would also contain calcite.

In the block of Yucca Mountain proposed for the repository, calcite and opal were found in less than 10 percent of the fractures and cavities, the USGS study said.

The Department of Energy has given UNLV $1.4 million to conduct a two-year study to date the ages of fluids and gas trapped in tiny bubbles inside calcite found in the mountain.