Nature may help protect the Columbia River from some long-lived radioactive contamination at Hanford, according to research at the Pacific Northwest National Laboratory campus in Richland.
Kevin Rosso, the associate director for PNNL's Physical Sciences Division and other researchers, investigated the ability of iron-rich minerals in Hanford soil to change technetium 99 into a form that sticks in the soil.
It's information that Hanford officials might find useful as they make decisions about Hanford cleanup, considering that groundwater may be at higher risk where soil has less iron, Rosso said.
Radioactive technetium was one of the byproducts of irradiating uranium fuel to produce plutonium for the nation's nuclear weapons program. It's a long-lived radioisotope with half of its radioactivity decaying over 211,000 years.
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It has contaminated soil and groundwater in central Hanford, where an estimated 1 million gallons of waste from chemically processing irradiated fuel to remove plutonium has spilled and leaked into the soil. In addition, more than 450 billion gallons of contaminated liquid was released into the soil in central Hanford.
The technetium left from reprocessing fuel is water soluble, allowing it to be carried with water from rain or snow melt deeper into the soil toward groundwater. The groundwater then moves toward the Columbia River.
Now some technetium is being removed from groundwater in central Hanford at the new 200 West Pump and Treat Facility, but removing technetium in the soil deep underground to prevent it from reaching groundwater is difficult.
"Water percolates through the sediments, and anything that dissolves in the water has a chance to reach groundwater," Rosso said.
But Rosso found that in the lab, ferrous iron reacts with the soluble form of technetium found in Hanford soil to convert it to a nonsoluble form.
"It gets it off the freeway," he said.
Researchers collected samples from two locations in central Hanford to check for iron-bearing minerals -- the open trenches used to dispose of reactor compartments from the Navy's nuclear-powered submarines and cruisers and the Environmental Restoration Disposal Facility, a 70-foot-deep lined landfill for low-level radioactive waste.
The locations were picked because researchers could easily gather below-ground samples.
The samples contained up to 1 percent of magnetic minerals, and 90 percent of that was magnetite, a small black grain with ferrous iron on the surface that interacts with technetium to make it less mobile in the soil.
Research was done at the Environmental Molecular Sciences Laboratory, a national facility on the PNNL campus with cutting-edge microscopy and spectroscopy equipment.
Next PNNL researchers plan to look at whether an iron-rich clay mineral layer, which is found about 60 feet deep at Hanford along the Columbia River, also reacts with technetium to make it less mobile.
-- Annette Cary: 509-582-1533; firstname.lastname@example.org; Twitter: @HanfordNews