It appears the presence of technetium-99, a devilish radioactive element, may be more widespread than previously thought in processing equipment at the K-25 uranium-enrichment plant. If so, that could complicate plans for taking down the east wing of the massive, U-shaped building and potentially delay the project's schedule and jack up the cost.

The Department of Energy and environmental regulators have been studying the issue since March, but there's still uncertainty, according to Steve McCracken, DOE's environmental manager in Oak Ridge.

DOE and its cleanup contractor, Bechtel Jacobs Co., along with the state of Tennessee and the U.S. Environmental Protection Agency, are working on a "characterization plan" to better understand where the technetium is and where it isn't, McCracken said.

The radioactive technetium, along with other products of nuclear fission, was introduced into the Oak Ridge equipment decades ago when reprocessed uranium - that had previously been in a nuclear reactor - was used as feed material to enrich uranium for nuclear fuel.

The remnants of Tc-99 are problematic because regulations allow only tiny amounts in DOE's Oak Ridge nuclear landfill, where most of the massive amount of contaminated rubble from K-25's demolition is destined for disposal.

John Owsley, who oversees DOE's activities for the Tennessee Department of Environment and Conservation, said technetium is a concern because its radioactivity is long lived and the element is especially mobile in the environment due to its solubility in water. It also can be difficult to detect, he said.

The standard in place at the Oak Ridge landfill is protective of the environment and human health, Owsley said, but he emphasized that regulators want to make sure no waste is disposed there that exceeds the criteria.

Materials too hot for the Oak Ridge landfill have to be shipped off site to Nevada Test Site or another location for disposal, and that's a lot more costly and time-consuming.

Oak Ridge officials previously believed that the presence of technetium was confined to a relatively small section in the massive plant's southeast corner, and they planned to treat it separately. If other areas also have the high-hazard contamination, they need to be identified before demolition work begins on the east wing, McCracken said.

The original plan for taking down K-25 was to first dismantle and remove the contaminated processing equipment and dispose of it before demolishing the building's metal-and-concrete structure.

That approach was dramatically altered, however, after a worker was seriously injured in early 2006 when he felt through a weakened floor in the old, deteriorated building. The revised technique is to inject equipment with a stabilizing foam, allowing workers to collapse everything in place. The piles of debris are then hauled to the landfill.

About a third of the west wing of the mile-long, U-shaped building - the largest building in the world at the time of its construction - has already been demolished, but McCracken said technetium-99 isn't an issue there.