Hanford workers have emptied a 16th single-shell tank of radioactive waste — at least to the limits of technology — leaving 133 to go.
About 27,460 gallons of waste have been removed from Tank C-111, which was built during World War II.
With 15 single-shell tanks emptied in the group of underground tanks called the C Tank Farm and an additional tank in the S Tank Farm, just one tank remains in the C Tank Farm that is covered by deadlines in the court-enforced consent decree.
“We will continue to work with the Department of Energy to stay on a path to closure of the first Hanford tank farm,” said Cheryl Whalen, cleanup section manager for the Washington State Department of Ecology’s Nuclear Waste Program, in a statement.
The consent decree, among other deadlines, requires all of the tanks in the C Tank Farm and nine of those in the A and AX tank farms to be emptied to regulatory requirements by March 2024. Preparations are under way to start retrievals in the A and AX tank farms.
Hanford has 149 underground, single-shell tanks used to hold waste from chemically processing irradiated uranium fuel at Hanford to remove plutonium for the nation’s nuclear weapons program.
Waste is being transferred from leak-prone single-shell tanks to 27 newer double-shell tanks for storage, until up to 56 million gallons of waste can be treated for disposal at the Hanford vitrification plant under construction.
149 number of Hanford single-shell waste tanks
16 number of tanks emptied to regulatory requirements
The goal was to remove all but 2,700 gallons of waste from Tank C-111, which would have left about an inch of waste if it were spread evenly across the bottom of the tank.
It had a capacity of about 530,000 gallons, but held far less waste when solid retrieval began.
However, the consent decree allows the requirement to be waived by the state if three technologies have been used to their limit to remove waste in a single tank.
In the case of Tank C-111, an estimated 5,000 gallons of waste remains in the tank, or a little less than 2 inches if it were spread evenly over the bottom.
In reality, remaining waste in the enclosed underground tanks may be in areas that are difficult to reach with retrieval equipment, such as clinging to walls, or at the edges of the tank farthest from where retrieval equipment can be lowered through 12-inch diameter risers into the tanks.
Hanford’s single-shell tanks had pumpable liquid retrieved earlier, and in recent years work has been underway to remove solids that can include salt cake and thick sludge.
At Tank C-111, work started in 2010 with a modified sluicing system lowered through a riser to spray liquid from high pressure nozzles on waste to break it up and move it toward a central pump for removal. Work halted when the system hit a hard crust of waste that it could not mobilize, even after soaking it in hot water.
I’m certainly pleased at the progress toward completing C Farm retrievals.
Kevin Smith, manager of the DOE Office of River Protection
Work resumed by tank farm contractor Washington River Protection solutions in October 2015 with a high-pressure water spray.
That was followed by adding caustic to the waste twice to loosen it, considered the third technology.
“I’m certainly pleased at the progress toward completing C Farm retrievals,” said Kevin Smith, manager of the DOE Hanford Office of River Protection, in a statement.
The C Farm tank yet to be emptied to consent decree requirements is Tank C-105.
Washington River Protection Solutions has tried to remove its waste with new technology, a vacuum system attached to a robotic arm called the Mobile Arm Retrieval System, or MARS. About 45 percent of the waste in the tank has been retrieved with about 67,000 gallons remaining.
MARS was largely successful in a demonstration project on a different tank, but for that tank the robotic arm was equipped with a sluicing system. A vacuum system was tried on Tank C-105 because it is suspected of having leaked in the past.
The MARS vacuum system worked in testing on mock waste, but was not a match for what DOE has described as the “high shear strength and stickiness” of the waste in Tank C-105.
Work has been underway this year to remove the contaminated MARS vacuum system from the tank to allow another technology to be tried.