Hanford workers have finished vacuuming the bulk of radioactive sludge from the floor of the basin into underwater containers, leaving bare concrete.
"This is another example of the momentum we continue to sustain in cleaning up the site and eliminating risk to the Columbia River," Dave Brockman, manager of the Department of Energy's Hanford office, said in a statement.
Completion of the sludge removal task allows DOE to meet a revised legal deadline and a commitment to the Defense Nuclear Facilities Safety Board to have the sludge in containers by the end of this month.
"We're pleased," said Larry Gadbois, environmental scientist for the Environmental Protection Agency, which regulates the project. "It's another step in risk reduction."
Both of Hanford's K reactors had irradiated fuel stranded in their cooling basins after fuel processing stopped at the end of the Cold War. The fuel in the K East and K West basins corroded and mixed with dirt and concrete from the basin walls to form radioactive sludge.
After the fuel was removed, Hanford workers struggled to vacuum the sludge into underwater containers to allow it to be treated.
Hanford workers spent two years vacuuming the bulk of the sludge from the leak-prone K East Basin into containers.
But it took just seven months to vacuum sludge in the K West Basin into underwater containers. That was due, in part, to K West being cleaner. It held about 10 cubic yards of sludge, compared to the 37 cubic yards of sludge that contaminated the K East Basin.
At the K East Basin, contractor Fluor Hanford discovered that the tons of debris that littered the basin was too difficult to vacuum around and stopped work while it was retrieved.
To vacuum the sludge, workers stand on grating over the indoor pools and reach to the bottom of the 20-foot pools with long-handled tools. The water shields them from radiation. Some of the sludge is hard-packed and has to be broken up and some is so light that it mushrooms up in fine clouds when disturbed.
Underwater cameras guide the work in the sometimes murky water, and workers have to wear respirators to make sure they don't inhale any airborne contamination.
The vacuuming took "time and patience and real perseverance," said Mark Peres, Fluor deputy vice president for the K Basins Closure Project.
Work is continuing at the K West Basin. Preparations are under way to remove about 1,800 pounds of stray fuel scraps found hidden among the sludge in the basins. That's a small percentage of the 4.5 million pounds of fuel already removed from the basins before sludge vacuuming began.
Some additional debris, including tools and more canister lids, also is being removed from the K West Basin.
Because more sludge will settle out of the water to leave a fine coating over the basin, a final vacuuming must be done by the end of January to meet another legal deadline.
Sludge from both the basins will be held in underwater containers at K West until a treatment system is ready to prepare the sludge for disposal.
DOE faces a November 2009 deadline to have the sludge treated.