Monday, January 14, 2008
Hanford workers prepare for high-risk excavation of waste
January 10, 2008
Hanford workers are preparing to start next week digging up radioactive and chemical waste that could spontaneously catch fire when exposed to air.
"We're planning for the worst case," said John Darby, project manager for the Department of Energy's contractor, Washington Closure Hanford.
The 618-7 Burial Ground was used from 1960 to 1973 for waste from the Hanford nuclear reservation's 300 Area just north of Richland where fuel was made for Hanford's reactors and research was conducted.
"Burial grounds like this don't have a lot of documentation," said Stacy Charboneau, DOE deputy assistant manager for Hanford cleanup along the Columbia River.
When the waste was disposed of, it was not expected to be retrieved to meet future environmental standards. But Washington Closure has developed a list of the hazardous items it needs to be prepared to handle there, starting with hundreds of barrels of metals in liquids to keep out air that could start a fire.
It expects to find drums of depleted uranium chips likely left from research work.
Workers also will be on the lookout for drums of zircaloy or beryllium shavings, both metals used in the cladding or capping of N Reactor fuel.
The drums likely were filled with oil or water before they were buried. But if they have corroded, the liquid may have leaked out and could leave the contents vulnerable to spontaneously igniting when exposed to the right temperature and oxygen.
"We will be using aggressive controls," Darby said.
Workers will be bringing up the barrels one at a time from behind blast shields and wearing full radiation protection gear and supplied air respirators. They'll also expose no more than four drums at a time during the excavation to limit any potential fire.
Intact drums will be opened with remotely operated equipment inside an enclosure so more water or mineral oil can be added to stabilize them. Contaminated soil where barrels have leaked will be mixed with a fixative to prevent airborne contamination.
Piles of sand already stand ready at the burial ground to quickly smother any fire.
Washington Closure believes chances of a fire are slim, in part because of the size of the chips they expect to unearth. But similar material has caught fire at Idaho and Tennessee nuclear sites.
Among the risks is uranium that may have been roasted to create uranium oxide to reduce the possibility of catching fire and allow the uranium to be buried without liquids. Despite fires elsewhere, Washington Closure believes the oxidation process at Hanford was more effective and may have done a better job of stabilizing the material.
Some of what Washington Closure knows about the burial ground comes from incomplete historical documents, often written with code words such as "pure W product" for plutonium, during the Cold War. Workers have verified those by interviews with former Hanford workers who have given accounts of the waste they remember being generated at the 300 Area.
Among the contents retired workers have warned about are drums of thorium nitrate solution or thorium oxide left from research into fuel to be irradiated for a possible new type of nuclear weapon. If those drums of radioactive material have ruptured, they could pose a hazard for airborne contamination.
Washington Closure also has dug some exploratory pits to get a better idea of what's in the burial ground and used ground-penetrating radar to confirm the size and location of burial trenches and help determine what might be inside them. The burial ground includes three waste trenches, the two largest 650 feet long, 100 feet wide and 20 to 25 feet deep.
The burial grounds also are expected to hold miscellaneous trash, including chemical drums, solvents and oil.
Once waste is dug up, it will be treated for disposal and most of it buried away from the Columbia River at a lined landfill for low-level radioactive waste in central Hanford. Treatment methods may include incinerating the oil and encasing uranium chips in grout.
The Environmental Protection Agency, the regulator for the work, and DOE say Washington Closure has made the correct preparations to do the work safely, despite the high risk contents of 618-7 and its proximity to the Columbia River and Richland. DOE and Washington Closure believe that by working with a single drum at a time, the quantity of hazardous material is too small to present a risk to the public.
DOE has brought in experts to observe preparations, drills and mockups and is confident the contractor is ready to start excavating, Charboneau said.
"There have been a lot of lessons learned," not just at other DOE sites but in digging up other burial grounds at Hanford, said Alicia Boyd, EPA environmental engineer.
New processes and equipment have been incorporated into Washington Closure plans "so it should be much safer," she said.
DOE is required to have the burial ground cleaned up to meet a December 2008 deadline under the legally binding Tri-Party Agreement.