Underground Nuclear Waste Pond Resists Thawing Efforts

The Knoxville News-Sentinel (TN); March 7, 2005

OAK RIDGE -- The big chill is over. The big thaw has begun.

Federal contractors last year pulled the plug on an environmental project that for seven years kept a pond of nuclear waste in a frozen state.

The project was designed to stop radioactive pollutants from migrating into nearby streams and ultimately into downstream reservoirs used for recreation and drinking supplies. It was an interim measure until plans were in place to excavate the site and solve the problem permanently.

That time is now, although the transition isn't an easy one.

The refrigeration units were turned off last spring, but the underground waste zone remains defiantly frosty.

"We monitored the pond through the end of the summer, the hottest months, and it had lost only about 10 percent of its ice thickness," said Jeff Cange of Bechtel Jacobs Co., the U.S. Department of Energy's environmental manager in Oak Ridge.

"We dismantled the cryogenic system in September, but we don't think anything has changed since then. It's still frozen."

Regardless, Bechtel Jacobs and its subcontractor, Sevenson Environmental Services, plan to start excavating the nuclear site within the next couple of weeks and complete the $4 million cleanup by late May. The radioactive soils will be transported by truck to a new landfill, lined with multiple layers of protection, several miles away on the DOE reservation.

"We going to dig it up frozen," said Charlie Johnson, another manager with Bechtel Jacobs.

Regulations prohibit transporting or disposing of the waste while it's still frozen, so officials hope warm weather and other measures -- such as breaking up the excavated sections -- will help thaw the soil.

The pond was created in the 1950s to receive nuclear wastes from the Homogeneous Reactor Experiment, an old test reactor at Oak Ridge National Laboratory. Around 1970, the 300,000-gallon pond was backfilled with clay and shale and other materials and capped with asphalt. But waste pipelines associated with the operations were left in place, and over time the pond's nuclear contamination began to migrate down a slope toward streams, including Melton Branch.

The biggest concern was strontium-90, a radioactive element that tends to concentrate in the bones if ingested by humans. There also was a significant quantity of cesium-137 and possibly smaller amounts of other radioactive and hazardous materials.

The potential hazards were noted in a number of environmental surveys, but it wasn't until the mid-1990s that steps were taken to mitigate the problem.

Arctic Foundations, based in Alaska, was hired to stem the leakage. The contractor installed a series of thermoprobes at the plot, 75 feet by 80 feet. The system froze the soil, groundwater and everything else to a depth of about 30 feet.

The cost of the original project was $1.2 million, with annual maintenance costs of about $27,000.

Bechtel Jacobs officials said they consider the project a success by any measure. Tests have shown that the ice barriers greatly reduced the off-site movement of strontium-90.

Although the refrigeration equipment has been removed, a thermal foam blanket remains at the frozen pond. Cange said removing it might speed the thawing process, but would allow rainwater to infiltrate the site, and that's a no-no.

Earlier this year, as a preparatory step in the cleanup project, Sevenson excavated about 9,000 cubic yards of contaminated soil from areas around the frozen pond, Johnson said. That was transported to one of ORNL's waste burial grounds and used as filler for an area being capped, he said.

Senior writer Frank Munger may be reached at 865-342-6329.
Copyright (c) 2005 The Knoxville News-Sentinel
Record Number: 417053385