Approximately 2,000 gallons of treated tank waste from the US Hanford Site have been solidified in grout and permanently disposed of at licensed commercial facilities as part of the Department of Energy (DOE) Office of Environmental Management’s (EM’s)Test Bed Initiative.
“This is an innovative effort to demonstrate options with the potential to accelerate the Hanford tank-waste mission in a safe, effective and efficient manner,” said Katie Wong, programme manager with the Hanford Field Office Tank Farms Programs Division. “This major accomplishment reflects the strong collaboration with our tank-waste contractor and commercial disposal partners.”
Following in-tank treatment at Hanford to reduce radioactivity by more than 99%, contractor Hanford Tank Waste Operations & Closure (H2C) shipped it to Waste Control Specialists in Texas and EnergySolutions in Utah where it was grouted and disposed of in accordance with regulatory requirements. “Every step of this initiative was carried out with great leadership, teamwork and a shared commitment to safely advancing our cleanup mission,” Wong noted.
As part of an agreement regulating Hanford cleanup, 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 based on available technology. The final stage is treatment at the Waste Treatment and Immobilisation Plant.
Hanford is home to 177 underground waste storage tanks – a legacy of nuclear weapons development and nuclear energy research during World War II and Cold War. These include 149 single-shell tanks (SSTs) and 28 double-shell tanks (DSTs), ranging from 55,000 to 1.265m gallons in capacity. The tanks are organised into 18 different groups, called farms.
The first SSTs were put into service in 1944 and were designed to be in use for about 20 years. They were built with a carbon-steel liner surrounded by a layer of thick, steel-reinforced concrete and buried 10 feet below the ground. In the 1950s some of the SSTs began leaking waste into the surrounding soil. The waste in the tanks has now been stabilised by removing all free liquid from it, minimising the chance of further leakage.
Construction of DSTs began in 1968. Each DST has a carbon-steel inner tank with a separate steel liner surrounding it to prevent leaks to the environment. The tank liners are separated by an air space of about 30 inches, equipped with a leak-detection system.
As part of the Hanford Tank Integrity Program, a team of engineers, supported by a group of independent experts, regularly reviews pertinent information regarding construction and operation of the tanks. The experts monitor the integrity of the tanks by examining waste chemistries, corrosion rates, storage histories and changing conditions. Periodic tank inspections are performed with ultrasonic testing, visual inspection and waste sampling. These inspections alert engineers to any potential issues regarding structural integrity of the tanks.
A critical part of managing the waste relates to the amount of available storage space in the tanks. Hanford’s 242-A Evaporator is critical to managing tank space. The evaporator takes in waste from the DST system and boils it. The water vapour from the boiling waste is collected, condensed, filtered, and sent to another Hanford facility for treatment, resulting in a reduced volume of tank waste. The remaining concentrated waste is transferred back to a DST.
In the last several years, the 242-A Evaporator has undergone major upgrades. Workers have modernised the ventilation, monitoring and control systems, have rebuilt systems, and have procured critical spare parts. The 242-A Evaporator frees up space in the DSTs and allows waste to be transferred from the older SSTs to the newer DSTs.
