By Tim Bonfield
The Cincinnati Enquirer

Crews at the former Fernald uranium processing plant have begun an important step in removing the most dangerous radioactive waste remaining at the Tristate's biggest environmental clean-up project.

Over the weekend, workers activated a radon-gas control system to clear out the radioactive gas trapped in the headspace of Fernald's K-65 silos - the aging, mostly buried tanks of contaminated slurry that have caused several controversies for the decade-long, $5 billion cleanup project.

The $20 million system, which took 14 months to design and build, is expected to remove 95 percent of the cancer-causing radon gas from the tanks, said Ray Corradi, silos project manager for Fluor Fernald, the contractor overseeing the clean-up project.

From the early 1950s to the 1980s, the sprawling Fernald plant about 18 miles northwest of Cincinnati processed uranium ore as an early step in producing atomic bombs.

The K-65 silo waste is a wet, heavy gravel-like substance that came from the Belgian Congo in the 1950s. Ever since, radium decaying within the slurry has been generating radon gas.

Over the years, the density of the radon gas has built up to 20 million picocuries per liter.

By comparison, the U.S. EPA recommends homeowners take steps to clear radon from their basements when levels reach 4 picocuries per liter.

To prevent the radon gas from escaping, cracks in the silos' covers were sealed from the outside with a special foam in 1986. Then an internal layer of bentonite was pumped into the tanks in 1991.

While Fernald officials began projects years ago to treat tainted groundwater, remove contaminated soil and haul away leftover barrels of waste, disposing of the silo waste has been a long-running, expensive controversy.

A plan to cook the waste into glass-like chunks in a process called vitrification was dropped after a pilot plant failed amid millions in cost overruns. Officials have since decided to seal the silo waste in concrete to ship it to waste disposal sites in Nevada, but that job still hasn't started.

First, the waste has to be transferred to four recently constructed 750,000-gallon steel tanks, a process scheduled to start in May 2004.

A year-long effort to blend the waste with concrete could start by February 2005, Mr. Corradi said.

If all goes according to plan, the Fernald clean-up project will be done by February 2006, with some low-level radioactive waste to be permanently stored there and most of the 1,050-acre site returned to an undeveloped park-like state.

E-mail tbonfield@enquirer.com