COVER STORY | HANFORD TANKS
Vitrification target 2026
Clean-up operations at the huge Hanford site in the US state of Washington are set to move into a new phase,
in which long-lived waste will be vitrified in a new Waste Treatment Plant
IN AGREEMENT WITH THE US Department of Energy, the Department of Ecology of Washington State has responsibility for the clean-up process at Hanford, a nuclear site where plutonium production activities began in 1943. A key task is the safe storage, retrieval and treatment of waste in 177 underground tanks, which contain radioactive and chemical wastes from four decades of plutonium production activities at the site. The waste was generated when irradiated uranium fuel rods were reprocessed, during which the uranium fuel rods were dissolved and plutonium chemically retrieved. The resulting liquid chemical waste was put into the underground storage tanks in ‘tank farms’ in Hanford’s ‘200 Area’. The tanks range from 55,000 gallons (208 m3 than a million gallons (3785 m3
) to more ). To build them, workers
cleared out large flat depressions, erected the tanks in situ and surrounded them with soil, leaving the tops of the tanks 3 m below ground to provide radiation shielding. Of the tanks, 149 are single-walled. These tanks do
not comply with Washington law, which requires that all underground storage tanks have a secondary container. In the late 1980s to mid-90s, much of the liquid was removed in hopes of making them more stable and reducing the risk of leaks. The remaining waste is similar to the consistency of sand.
The remaining 28 tanks are double-walled. Although they
comply with state law in that regard, they, like the single- walled tanks, are well past their design life of about 25 years and at least 68 tanks are assumed to have leaked in the past. Two tanks are currently known to be leaking and are being managed under an agreed process (see box). If waste were to remain in the tanks, untreated, it would eventually enter the ground, the groundwater and the Columbia River. Previous leaks have caused ground contamination. Tank waste retrieval is extremely difficult. Nevertheless,
remaining waste from single-shell tanks is being sent to double-shell tanks through a system of hose-in-hose transfer lines. As the waste is moved excess water is evaporated.
Riser pipes provide access into the tanks, but many are
only a foot in diameter and none were designed to make it easy to empty the tanks. Retrieval equipment inside the tank is operated remotely and the hostile conditions quickly wear out electronics and other equipment. Structures in the tanks also obstruct access. Overall, an estimated 56 million gallons (212,000 m3
) of
mixed hazardous and radioactive waste remains in the tanks. As part of an agreement regulating Hanford clean-up, crews must remove at least 99% of the waste in every tank on the site, or at least as much waste as can be removed
Above: The vitrification plant at Hanford under construction 16 | May 2024 |
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