Fundamental Solutions
for Spent Fuel

Researchers at the Battelle-managed Pacific Northwest National Laboratory (PNNL) have supported engineered solutions for spent nuclear fuel used to produce nuclear materials on the Hanford site since the mid-1990s. For the U.S. Department of Energy (DOE) and Hanford cleanup contractors, PNNL has applied radiochemical processing capabilities to help better understand the behavior of uranium-based fuel and enable safe processing to stabilize the fuel. PNNL science is providing DOE with a defensible basis for processing the fuel and ultimately protecting the Columbia River from potential contamination.

Since production of material for nuclear weapons ceased, approximately 4.6 million pounds of used fuel has been stored in two leak-prone concrete pools. Hanford’s K Basins also hold 2.6 million gallons of radioactive water, just 400 yards from the Columbia River.

DOE needed to reduce the risk posed by the used fuel and decided to move it to interim dry storage in underground vaults 12 miles inland. DOE also plans to remove sludge, which is a combination of dust, sand, and oxidized or degraded fuel, and ultimately dispose of the Basins.

A key concern was rapid chemical reactions that could occur when the fuel was removed from the water. Applying specialized radiochemical expertise, Battelle researchers characterized the fuel, defining the kinds of chemical reactions that could take place as the uranium was drying. The researchers’ work led to a more complete understanding of the hazards associated with drying and prescribed the condition the fuel must achieve to assure safe storage for decades. Information about hydrogen and heat generation during drying contributed to a decision to clean the fuel before placing it in dry storage.

Processing the fuel requires that it first be removed for cleaning from the aluminum and stainless steel canisters where it is stored. The canisters left behind could then be removed from the basins at a later date.

DOE is evaluating options for dispositioning the Basins, including the potential to embed the canisters within a layer of concrete grout. Fluor Hanford, DOE’s cleanup contractor for spent fuel, identified concerns about using concrete grout because the aluminum in the canisters could potentially react with the concrete to generate heat and hydrogen. Could DOE safely fill the basins with concrete leaving all the canisters in place? Battelle researchers provided analyses that established the safe upper limit for the amount of aluminum to be left in the basins, as well as the number of canisters that would have to be removed before the fill.

Battelle researchers also applied expertise in radiochemical analysis, thermodynamics, fluid dynamics, and computer modeling to characterize the sludge, identify the corrosion products and expansion rates of the sludge aging process, and provide information on how much oxygen and hydrogen the sludge would generate. Their work led to an understanding of the amount of sludge that could be safely placed in a storage container.

For more information, contact Mr. Terry Walton at (509) 372-4548, terry.walton@pnl.gov.