Washington River Protection Solutions has emptied the 15th of 16 waste tanks in the Hanford Site’s C Tank Farm to regulatory standards. A court-enforced consent decree deadline requires the last of the C Farm tanks to be emptied to regulatory standards by March 2024. Tank C-111 is also the 16th of Hanford’s 149 leak-prone single-shell tanks to be emptied. One S Farm tank also has been emptied.
Hanford workers removed about 27,460 gallons of liquid and solid waste from Tank C-111 since 2010, leaving about 5,000 gallons in the tank. The goal was to remove all but about 2,700 gallons of waste from the tank, which would leave about 1 inch of waste if it were spread evenly over the bottom of the 530,000-gallon- capacity tank. However, the 2010 federal court consent decree allows the Washington state Department of Ecology to waive the requirement if three technologies have been used to their limit, which the state agreed to do for Tank C-111.
WRPS began emptying sludge from Tank C-111 began in 2010, after a previous campaign to remove pumpable liquids from all single-shell tanks at Hanford. Selected modified sluicing was selected as the removal technology for the tank, which had a relatively low volume of waste at the time. The technology relied on high-pressure nozzles lowered into the enclosed tank to spray liquid onto the sludge and wash it toward a pump lowered into the center of the tank. But work stopped when the system hit a hard crust of waste that it could not mobilize, even after a hot water soak.
Retrieval resumed in 2015 with a high-pressure water spray, which could be used in the tank because it is not known to have leaked in the past. That was followed by the third technology used in the tank, adding caustic two times to help loosen the waste. The retrieved waste has been transferred to double-shell Tank AN-101 for storage until it can be treated for disposal at the Waste Treatment Plant currently under construction.
“We’re glad the efforts continue to retrieve waste from the aging single-shell tanks,” said Cheryl Whalen, Nuclear Waste Program cleanup section manager for the Department of Ecology. “We will continue to work with the Department of Energy to stay on the path to closure of the first Hanford tank farm.” Kevin Smith, manager of the DOE Office of River Protection, said he was pleased with progress to complete C Tank Farm retrievals.
The remaining C Farm tank not emptied to regulatory standards is Tank C-105, where Washington River Protection Solutions has tried using a vacuum system with the Mobile Arm Retrieval System, or MARS, a large and robust robotic arm. Vacuum technology is intended to limit the liquid introduced into the tank to mobilize waste because the tank is suspected of leaking in the past.
This was the first time a vacuum system has been used with MARS. Although the technology showed promise in testing before it was inserted into the tank, it proved no match for some of the waste in the tank that was firmer than anticipated. The contractor has been working to remove the MARS system from the tank this year to allow for trying another technology. The tank still holds about 67,000 gallons of waste.
