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Hanford workers to learn more about radioactive sludge
published Tuesday, July 14, 2009  2695 Views :: 3 Comments
By Annette Cary, Herald staff writer
7/14/09

Hanford workers have collected a first batch of samples of radioactive sludge from Hanford's K Basins to help design the system that will be used to get the sludge out of the basins and treat it.

New contractor CH2M Hill Plateau Remediation Co. wants to know as much as possible about the sludge as it prepares to treat it, hoping to avoid the sort of false starts and technical problems that have plagued earlier work with the sludge for the Department of Energy.

CH2M Hill has submitted a plan for treatment of the sludge to DOE, which assembled a team of technical experts to review the proposal. The team's report is now being reviewed by DOE officials in Washington, D.C., who have not released information on the proposed plan.

"Sludge is still a pretty big challenge for DOE and its contractors," said Rod Lobos, environmental engineer for the Environmental Protection Agency, the DOE regulator for the work.

DOE was legally required to begin treating the sludge by the end of 2008 and have all of it treated before December this year. It became apparent those Tri-Party Agreement deadlines could not be met after an independent expert review raised questions about the previous plan for treating the sludge.

Now about 38 cubic yards of sludge from both the K East Basin and the K West Basin have been vacuumed up and are stored in underwater containers at the sturdier K West Basin. Workers are excavating the K East Basin after the last of the sludge was removed from it and its water drained.

For the sampling program, CH2M Hill workers have collected 54 bottles of sludge and basin water and have sent them to Pacific Northwest National Laboratory for analysis. Each bottle holds about a gallon.

"Sampling the sludge supports characterization and will provide a higher level of confidence when we treat the sludge," said David Del Vecchio, CH2M Hill vice president for work at the K Reactors. It also will help the contractor develop the systems needed to remove the sludge from underwater containers and then store it away from the river until it is treated.

The K Basins are 400 yards from the Columbia River and as long as the K West Basin continues to store the sludge, the basin and potentially contaminated soil beneath it cannot be cleaned up and the K West reactor cannot be either sealed up for long-term storage or torn down.

The basins attached to the K East and K West reactors were used to cool fuel that was irradiated to produce plutonium for the nation's nuclear weapons program. But at the end of the Cold War, 2,300 tons of unprocessed fuel was left in the basins to corrode and contribute to sludge that collected in the pools from dirt, sand and concrete that sloughed off the walls of the basin.

The sludge is difficult to handle. It's not uniform, but is made up of particles that can range from very fine sub-micron particles that disperse in the water when disturbed to particles up to a quarter of an inch, including fragments of irradiated fuel. The sludge is highly radioactive and contains uranium. The uranium particles are heavy and difficult to move through piping, are abrasive to pumps and can generate flammable hydrogen.

The initial samples have been collected from four stainless steel containers of sludge vacuumed from the two basins. A second phase of sampling is planned to collect additional sludge, including from settler tubes that were part of a system used to clean sludge off the fuel before it was removed from the basins.

Although the settler tubes hold far less sludge, the sludge may be more radioactive and contain more uranium.

Workers prepared for the sampling by developing tools for the work with handles up to 25 feet long to reach through the grating above the K West Basin and down to the containers. Although the sludge is in containers, they remain in 17 feet of water that provides radiation shielding.

Workers practiced with the tools at the Maintenance and Storage Facility once used for work associated with the Fast Flux Test Facility. Standing on a platform above a mock sludge container, they practiced lowering a half-inch-diameter tube to the bottom of the container, sucking up the sludge and pulling it into a bottle.

Once they'd perfected the tools and their technique, workers practiced collecting water samples from the bottom of the K Basins before collecting samples from the underwater sludge containers.

It's one more step toward getting the K Basins cleaned up along with the rest of the Hanford land along the Columbia by 2015. "Sludge is the long pole in the tent," Lobos said. "It's what the river corridor is waiting on. The sooner we can get the sludge off the river, the sooner we can get the river corridor completed and cleared."


 



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