DOE tracks water flow at Yucca

Monday, May 21, 2001 | 10:56 a.m.

Government scientists are analyzing results of experiments at Yucca Mountain that could show whether rock fractures allow ground water to move faster than expected through the site of a proposed nuclear waste repository.

Water carrying radiation into the environment is a critical consideration in whether Yucca Mountain, 90 miles northwest of Las Vegas, can safely contain 77,000 tons of high-level nuclear waste.

Yucca Mountain is the only site being studied to hold the commercial and defense radioactive waste. It must be found scientifically suitable to safely hold the material for 10,000 years to be approved. The Energy Department is charged with studying the site and would build the repository if it is approved.

Scientists are concerned that if water drains into alcoves filled with buried nuclear waste, the water could corrode containers and release radioactivity into the environment. People live 12 miles southwest of the proposed repository in Amargosa Valley.

Although the evidence in recent DOE reports suggests a fast pathway for water to flow, the critical information scientists are seeking is whether the water would transport radiation away from the repository.

DOE testers poured water into Yucca Mountain at its surface, but analysis of the results is still under way.

At a technical meeting earlier this month in Arlington, Va., Mark Peters of the Los Alamos National Laboratory in New Mexico said that analysis of the water flows is not complete, but the findings should be ready by the end of the year.

A December 1999 progress report said experiments indicate water flows faster through the fractured rock, which could disqualify Yucca Mountain as a repository if the Environmental Protection Agency issues a strict limit on radiation doses from ground water.

The EPA has called for a limit of radiation released from waste stored at Yucca Mountain of 15 millirems per year, with a 4 millirem standard for ground water. A chest X-ray is roughly 5 millirems.

That ground water limit is so strict, the DOE may be unable to meet it, which is why Nevada officials support it. Bush administration officials still are reviewing the standard.

DOE scientists observed two examples of rapid water flows through the mountain, in 1996 and 1999, the progress report said.

In an alcove at the north end of the 5-mile-long exploratory study tunnel, DOE scientists discovered water in 1996 that they believe came from a broken hose used during construction of the tunnel. As much as 10,000 gallons of water escaped, possibly widening fractures in the rock and causing the water to move faster, the report said.

In a monthlong test in early 1999, scientists deliberately poured water equal to 12 inches of rainfall -- the amount expected during a glacial climatic period -- on top of the mountain.

Scientists believe an Ice Age has almost no chance of occurring in the first 10,000 years the mountain must safely hold the waste. After that period, it is too uncertain to predict.

The water went into an alcove, then escaped down one of three boreholes drilled into the alcove's side, moving 115 feet in a fracture in 15 days. In a previous test, the report noted, the water took 58 days to move that far.

Scientists concluded that the water's speed was caused by a fracture in the rock, significant because such a crack offers a fast pathway for water to flow. The DOE said further studies are under way.

Independent scientists from the Nuclear Regulatory Commission and the Nuclear Waste Technical Review Board have been following studies of water moving inside the mountain.

The NRC will license a repository at Yucca Mountain.

NRC hydrologist James Winterle said the DOE scientists poured the water into the top layer of the mountain, while the repository would be built about 1,000 feet lower, in a third layer of volcanic ash.

That top layer, called the Tiva Canyon formation, is cracked, he said. But the repository layer, the Topopah Spring tuff, is separated by what is called the Yucca Mountain-Pan Canyon layers, which absorb a lot of the water.

"Think of it as very sponge-like," Winterle said of the middle layer. The top layer is built like a stack of bricks, allowing fast water flows through cracks, but the water is absorbed in the sponge underneath, he said.

The DOE will have to prove to the NRC that this is the way Yucca Mountain works to protect public health and safety, NRC Executive Director Bill Reamer said. "The burden of proof is on the DOE."

There are many steps the DOE needs to take between its current studies and a licensing hearing, Reamer said. If the DOE, the president and Congress decide to recommend the mountain as a repository, the NRC will review information before formal licensing hearings begin, he said.

The technical review board, formed in 1988 as an independent scientific panel to oversee DOE's work, has also been waiting for DOE analysis to be completed.

"We've been following the progress of that test, of course," board hydrologist David Diodato said of the DOE's study based on the 1996 flow.

However, he said he had not seen the DOE's 1999 progress report, part of the basis for a final report on environmental impacts scheduled at the end of this year that will form the basis for a recommendation on Yucca Mountain to Energy Secretary Spencer Abraham.

Nevada's scientific experts are convinced that rain falling on the surface of Yucca Mountain would reach buried containers of high-level nuclear waste.

Based on radiation from atomic bombs exploded in the Pacific Islands that DOE researchers discovered at the repository level inside Yucca Mountain, as well as other studies that show the container material proposed to bury the wastes can corrode in roughly two weeks, state scientists estimate the radiation will be in the environment in 1,250 years, said Bob Loux, executive director of the Nevada Agency on Nuclear Projects.

The repository, to be considered scientifically sound, must contain the radioactivity for 10,000 years.

However, the state's conclusion about radioactive water from the 1950s Pacific weapons tests seeping into Yucca Mountain is disputed by scientists at the Livermore National Laboratory in Northern California.

Another theory that deep, hot water welled inside the mountain within the past 10,000 years has been put to rest by a team of scientists led by UNLV associate geoscience professor Jean Cline.