Hanford Technology Development (Tank Farms) - 12509
The mission of the Department of Energy's Office of River Protection (ORP) is to safely retrieve and treat the 56 million gallons of Hanford's tank waste and close the Tank Farms to protect the Columbia River. The millions of gallons of tank waste are a byproduct of decades of plutonium production. After irradiated fuel rods were taken from the nuclear reactors to the processing facilities at Hanford they were exposed to a series of chemicals designed to dissolve away the rod, which enabled workers to retrieve the plutonium. Once those chemicals were exposed to the fuel rods they became radioactive and extremely hot. They also couldn't be used in this process more than once. Because the chemicals are caustic and extremely hazardous to humans and the environment, underground storage tanks were built to hold these chemicals until a more permanent solution could be found. One key part of the ongoing work at Hanford is retrieving waste from the single-shell tanks, some of which have leaked in the past, and transferring that waste to the double-shell tanks - none of which have ever leaked. The 56 million gallons of radioactive tank waste is stored in 177 underground tanks, 149 of which are single-shell tanks built between 1943 and 1964. The tanks sit approximately 250 feet above the water table. Hanford's single-shell tanks are decades past their 20-year design life. In the past, up to 67 of the single-shell tanks are known or suspected to have leaked as much as one million gallons of waste to the surrounding soil. Starting in the late 1950's, waste leaks from dozens of the single-shell tanks were detected or suspected. Most of the waste is in the soil around the tanks, but some of this waste is thought to have reached groundwater. The Vadose Zone Project was established to understand the radioactive and chemical contamination in the soil beneath the tanks as the result of leaks and discharges from past plutonium-production operations. The vadose zone is the area of soil between the ground surface and the water table 200-to-300 feet below. The project tracks and monitors contamination in the soil. Technologies are being developed and deployed to detect and monitor contaminants. Interim surface barriers, which are barriers put over the single-shell tanks, prevent rain and snow from soaking into the ground and spreading contamination. The impermeable barrier placed over T Farm, which was the site of the largest tank waste leak in Hanford's history, is 60,000 square feet and sloped to drain moisture outside the tank farm. The barrier over TY Farm is constructed of asphalt and drains moisture to a nearby evaporation basin. Our discussion of technology will address the incredible challenge of removing waste from Hanford's single-shell tanks. Under the terms of the Tri-Party Agreement, ORP is required to remove 99 percent of the tank waste, or until the limits of technology have been reached. All pumpable liquids have been removed from the single-shell tanks, and work now focuses on removing the non-pumpable liquids. Waste retrieval was completed from the first single-shell tank in late 2003. Since then, another six single-shell tanks have been retrieved to regulatory standards. (authors)