Underground Waste Storage
Hanford is home to 177 underground waste storage tanks: 149 single-shell tanks (SST) and 28 double-shell tanks (DST) ranging from 55,000 to 1 million gallons in capacity. Those tanks are organized into 18 different groups, called farms.
During the effort to support World War II, Hanford was built with secrecy and speed while workers did their best to safeguard the environment by building nuclear waste storage tanks.
The first single-shell tanks were put into service in 1944 and were designed to be in use for about 20 years. In the 1950s single-shell tanks began leaking waste into the surrounding soil. The tanks were built with a carbon steel liner surrounded by a layer of thick steel-reinforced concrete and buried 10 feet below ground level. Currently, all SST tanks are well past their design life and do not meet regulatory requirements. The waste has been stabilized by removing all free liquid, minimizing the chance of further leakage.
Construction of double-shell tanks began in 1968. The double-shell tanks have a carbon-steel inner tank with a separate steel liner surrounding it. The tank liners are separated by an air space, or annulus, of about 30 inches armed with a leak-detection system. Unlike Hanford’s single-shell tanks, the double-shell tanks still meet federal and state regulations. But even the double-shell tanks are starting to show signs of aging. In 2012, it was discovered that the oldest of Hanford’s double-shell tanks – AY-102 – leaked a small amount of waste into its annulus. The annulus performed as expected and contained the waste. The tank was taken out of service, the waste within it was retrieved and transferred to another double-shell tank.
For more detailed information on the tanks see the sister website here.
Tank Integrity Program
A team of WRPS engineers, supported by a group of independent experts, regularly reviews pertinent information regarding construction and operation of Hanford’s waste tanks. These experts monitor the integrity of the tanks via a program that examines waste chemistry, 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 the structural integrity of the underground waste storage tanks.
Tank Storage Space
Another critical part of managing the waste relates to the amount of available storage space in the tanks. As the last operating nuclear processing facility at Hanford, the 242-A Evaporator is critical to the cleanup mission. The evaporator heats waste to a boil under a vacuum. Vapor from the boiling waste is collected, condensed, filtered, and sent to the Effluent Treatment Facility for treatment and disposal, resulting in a tank waste volume reduction. The remaining concentrated waste is transferred back to a DST.
In the last several years, the 242-A Evaporator has undergone major upgrades. Workers finished modernizing the ventilation, monitoring and control systems, have rebuilt systems, and have procured critical spare parts.
The 242-A Evaporator is the workhorse that allows SST waste to be transferred to DST tanks. For more detailed information on the 242-A evaporator see the sister website here.