Hanford workers have started to pull items out of underground silos near the K reactors, where highly radioactive debris from Cold War reactors was buried a half-mile from the Columbia River.
It's the final burial ground associated with Hanford's nine plutonium-production reactors to be cleaned up. And that's for good reason.
The K East and K West reactors were the workhorses among Hanford's reactors, which produced plutonium for the nation's weapons program.
Washington Closure Hanford's experience at other burial grounds to date has helped it develop processes that will be used at the last burial ground, called the 118-K-1 Burial Ground, said Mark French, the Department of Energy project director.
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The burial ground includes the first metal silos -- pipes that were buried vertically in the soil -- to hold reactor debris. They were used to dispose of waste deemed too radioactive to bury in nearby trenches in the 16-acre burial ground.
The burial ground received waste from 1955 to 1973, not just from the K reactors, but also the newer N Reactor.
Cost of the total cleanup is expected to be $14 million.
Work began last month on what's expected to be the most difficult part of the burial ground cleanup, a row of six silos. Each is 10 feet in diameter and 25 feet deep.
"We know that most of the highly radioactive waste is located at the bottom of the silos," said Scott Parnell, Washington Closure project manager.
His strategy is to take each step in the silo cleanup slowly, carefully and deliberately to ensure protection of workers and the environment, he said.
The silo waste could include irradiated nuclear fuel, metal that was irradiated during reactor operations and remnants of the reactor safety systems.
Through historical records, officials also know that a cobalt irradiator -- used to see how metals might react when they were irradiated during reactor operations -- may be in one of the silos.
After doing radiation checks by lowering instruments into long steel tubes driven into the ground near the silos, they suspect the cobalt irradiator may be what's causing a high radiation reading at the bottom of the sixth silo.
They also know there's an obstruction halfway down the sixth silo, said Rob Cantwell, Washington Closure deputy director of field remediation.
Work has started by removing dirt and items in the first 10 feet of some of the silos using a clam shell on the end of an excavator arm. The equipment operator is in a cab behind an 8-foot tall barrier of concrete ecology blocks built around the silos to provide radiation shielding and relies on a camera to guide his work.
The clam shell deposits debris it picks up in a nearby area where a waste trench already has been excavated. The debris then will be sorted and most of it loaded for transportation to Hanford's landfill for low-level radioactive waste, the Environmental Restoration Disposal Facility in central Hanford. Some of the debris may require special packaging before it is taken to the landfill, Parnell said.
After the silos are emptied, they and the surrounding soil will be dug up.
Some work was done at the 118-K-1 Burial Ground from 2006 to 2008, but Washington Closure returned to the project with more experience in cleaning up burial grounds in January 2010.
Under a subcontract through Dance Designs of Pocatello, Idaho, Watts Construction of Kennewick is supplying equipment and labor for the work.
Cleanup of 16 unlined trenches in the burial ground is about 65 percent complete. Workers have found reactor hardware, highly radioactive piping, hydraulic machines, partially full nitric acid drums, lead, batteries and soil discolored by chemicals.
Washington Closure expects all waste to be removed from the burial ground in June.
The project is on track to have the 118-K-1 Burial Ground cleaned up, covered up and replanted by a Tri-Party Agreement deadline of the end of 2012, said Chris Guzzetti, an environmental scientist with the Environmental Protection Agency, the regulator on the project.