The Department of Energy and its tank farm contractor met their deadline to start emptying waste from double-shell Tank AY-102 with several thousand gallons of liquid removed by Thursday afternoon. “The state is pleased with the efforts of DOE and Washington River Protection Solutions to meet the terms of the settlement agreement, even starting waste removal a day before the deadline,” said Tom Tebb, acting manager for the Washington State Department of Ecology’s Nuclear Waste Program, in a statement Thursday. The deadline, set by the state as part of a settlement agreement in September 2014, required the start of waste retrieval by March 4. “This road has been a long one, and your efforts are truly appreciated,” WRPS President Mark Lindholm said in a message to employees. The tank is leaking waste from its inner shell, which is collecting in the space between its shells. As of the end of 2015, the tank was estimated to have leaked about 60 gallons of waste that had collected in three places in the 2.5-foot-wide annulus between the shells.
WRPS could have removed the liquid waste from the tank much sooner, but the liquid helps cool the sludge at the bottom of the storage container. The sludge generates heat as it radioactively decays, and heat can increase corrosion rates in the tank and contribute to generating potentially flammable gas. The liquid waste, or supernate, makes up the majority of the approximately 800 gallons of waste in the tank. Beneath it is about 150 gallons of radioactive sludge. The supernate is expected to be removed from the tank by early next week. It is being sent through underground lines to a double-shell tank near the 242-A Evaporator facility, which is used to reduce the quantity of liquid waste to free up double-shell tank space. With Tank AY-102, the oldest of Hanford’s double-shell tanks, removed from service, Hanford has 27 double shell tanks remaining to store waste retrieved from Tank AY-102 and from leak-prone single-shell tanks until the waste can be treated for disposal.
“Our work is far from done,” Lindholm told employees. “Once the supernate is removed, retrieval will pause while preparations are made to begin sludge retrieval.” Sludge retrieval, which is expected to be far more difficult and time-consuming, is planned to begin later this month. WRPS will use the same type of sluicing system that has been employed to retrieve waste in some of Hanford’s single-shell tanks for more than a decade. It sprays recycled liquid on waste to dissolve it and move it toward a central pump in the tank for removal. In late spring or early summer, WRPS is expected to pause retrieval to replace conventional sluicing systems in Tank AY-102 with extended-reach sluicing systems.
They can reach deeper into the tank and fold out to reach more areas. Tank AY-102 has a more complex interior structure than Hanford’s single-shell tanks, with 22 vertical pipes that extend from near the bottom of the tank to its head space to help cool the container. The extended-reach sluicing systems also are equipped with a high-pressure water system that may be needed to break up possibly hardened sludge on the bottom of the tank.
Precautions will be taken to protect workers from chemical vapors as sludge is retrieved from the tank and transferred to double-shell Tank AP-102 through above-ground lines. Barricades will be set up to make sure workers for other contractors do not unwittingly enter areas where vapors might be present. Exclusion zones will be created around exhauster stacks and only tank farm workers wearing supplied-air respirators will be allowed inside those zones. Industrial hygienists will monitor for vapors. DOE and WRPS have one year to empty the waste from the tank. “The resources committed to removing waste from AY-102 highlights the priority DOE and its contractor put on keeping this project on track,” Tebb said.