Hanford workers are giving the Foldtrack a second try after a brief and unsuccessful performance inside a radioactive waste tank five years ago.
It's a grown-up combination of a Transformer and remote-control bulldozer, engineered to move waste around the bottom of enclosed, underground tanks.
Outside the tank, the 800-pound machine extends to 12 feet long to fit through the narrow risers that provide the only access into the tanks.
Before it's lowered completely onto the floor of the tank, it folds in half, placing its two crawling tracks in parallel with a plow blade for pushing waste in the front.
During practice runs in a mock-up of the 75-foot diameter tank in 2007, the device worked well, using its blade to push aside heavy pipes and rocks and then using its four nozzles to sweep the concrete floor clean with a spray of water.
But when it was lowered into radioactive waste Tank C-109, engineers discovered they had underestimated the difficult conditions in the tank. The Foldtrack broke down after nine hours of use.
Waste in the tank formed clumps and built up in the system, throwing off one of the tracks. The device was not intended to be removed from the tank after it was contaminated with radioactive waste, limiting options for repairs.
Workers tried to operate it with just one of its tracks, but that caused a hydraulic oil leak of 15 to 20 gallons inside the tank and work was halted. The Foldtrack remains in the tank, which has since been emptied to regulatory standards using a caustic soak that allowed waste to be pumped out.
Despite those problems, current tank farm contractor Washington River Protection Solutions still saw promise in the Foldtrack, which had been tried under previous tank farm contractor CH2M Hill Hanford Group.
The device has received an overhaul. The Foldtrack, which comes from Non Entry Systems in Wales, has been modified to prevent waste from building up in the track system and to prevent the track from coming off. Joints also have been strengthened.
And its equipment has been beefed up.
The Foldtrack has four nozzles to spray water. Three of the nozzles had been designed to spray liquid at 1,000 to 3,000 pounds per square inch directly at the waste to break it up. That has been increased to 1,100 to 5,000 pounds per square inch on the new model, said Peggy Hamilton, a Washington River Protection Solutions manager.
A fourth nozzle can provide a higher-volume, lower-pressure spray that could be useful for tasks such as washing down the walls of a tank.
The updated version of the Foldtrack has been lowered through a 12-inch-diameter riser into Tank C-110, which has 17,200 gallons of difficult-to-remove waste at its bottom. In 2008 Hanford workers removed the bulk of the solid waste from the tank, an estimated 161,000 gallons.
But the waste that remains on the bottom has a consistency like sand, and is sitting in drifts that may hide larger chunks of waste underneath. The waste needs to be pushed toward a pump in the center of the tank to be removed and transferred to a newer double-shell tank to await treatment.
A sluicing system is installed in the tank to spray the waste toward the pump, but it just moves the remaining waste from one side of the tank to the other, Hamilton said.
Washington River Protection Solutions plans to use the sluicing system in combination with the Foldtrack to retrieve as much as possible of the 17,200 gallons of waste, using the blade of the Foldtrack as a backstop for the sluicer to shoot liquid toward.
To prevent contaminating clean water that would add to the waste total, contaminated liquid from a double-shell tank is used by the sluicing system.
Support equipment for the system still needs to be installed outside the tank. And Washington River Protection Solutions plans to finish up work to empty two other tanks before the Foldtrack starts moving waste in Tank C-110.
However, in June it may be ready to put the new Foldtrack to work.