Researchers have vitrified 2 gallons of radioactive waste removed from a Hanford Site storage tank in a first-of-a-kind demonstration of the processes that will be used at the Waste Treatment Plant being built at the Energy Department facility in Washington state.
Pacific Northwest National Laboratory researchers said it was the first time Hanford tank waste has been converted to a glass form in a continuous process similar to the approach planned for the vitrification plant, rather than in batches. The test was performed for DOE and its tank farm contractor, Washington River Protection Solutions (WRPS).
“This successful test confirms the science and engineering approach,” said Will Eaton, who led the test for PNNL. “It’s an important milestone.”
Previous tests have been done with waste simulants and others with crucibles of radioactive waste heated all at once. “The thing you can’t do with (crucible tests) is understand how that dynamic process happens,” Eaton said. At the vitrification plant waste will be poured gradually into the hot melter, with different processing steps between liquid waste and glass that should better contain some radionuclides than heating all the waste at once.
Bechtel is building the WTP to treat up to 56 million gallons of waste produced during decades of plutonium production at Hanford. The material will be converted into a glass form for disposal. Under a federal court order, processing of low-activity waste must begin by 2023 and the plant must be fully operational by 2036.
Waste for the test was drawn from double-shell Tank AP-105. The initial waste to be vitrified at the Waste Treatment Plant is planned to come from am AP Tank Farm tank. The Energy Department plans to start treating low-activity radioactive waste at the plant as soon as the end of 2021.
For the test, researchers at PNNL used filtration and ion exchange systems similar to those that will be used to prepare waste for the vitrification plant to separate out the low-activity portion. The work was done in a hot cell of the national laboratory’s Radiochemical Processing Laboratory at Hanford’s 300 Area.
In the same building 2 gallons of liquid low-activity waste were mixed with glass-forming material in a fume hood to prepare a 3-gallon mixture for vitrification. The mixture was dripped into a 5-inch-diameter steel melter within a furnace that heated the mixture to 2,100 degrees Fahrenheit in an adjacent fume hood. The test started at about 9 a.m. April 11 and ended 24 hours later. It produced roughly 20 pounds of opaque black radioactive glass.
The Pacific Northwest National Laboratory developed the liquid-fed ceramic waste melter technology in the 1970s and has become the standard for waste vitrification in this country and internationally.
Analysis is underway on the chemical composition of the glass produced. The liquid condensate collected from the off gases will be concentrated and grouted later this spring. The grout will be analyzed to assess compliance with disposal requirements.
Plans also are being made to have PNNL try the complete vitrification demonstration again later this year. Waste for the next test will be drawn from the AP-107 Tank and PNNL has been asked to test a variation of the filtration and ion exchange method for pretreatment, including a different resin in the ion exchange process.
“Being able to run real tank waste instead of simulants through these tests provides valuable input for validating and refining our approach to the treatment of low activity waste,” said Kris Colosi, the WRPS project manager.
