HANFORD — A powerful new vacuuming system may be the answer to pulling heavy radioactive waste solids out of Hanford tanks that require careful handling to prevent more leaks.
Thursday in a high bay at the Big Pasco industrial park, the system sucked through a layer of heavy black sand, leaving a tidy, cleared path in its wake.
"It's similar to a carpet cleaner," said Steve Pfaff, Department of Energy project director for tank retrievals. "It uses a little bit of liquid to mobilize waste and sucks it up."
As simple as that sounds, it could be a major step forward for Hanford environmental cleanup.
Hanford has 53 million gallons of radioactive and hazardous chemical waste stored in underground tanks until it can be treated. The waste is left from the past production of plutonium for the nation's nuclear weapons program.
Washington River Protection Solutions is working to empty waste in 142 leak-prone single-shell tanks into 28 sturdier and newer double-shell tanks. But some of the work under the current and previous contractor has been difficult and slow, indicating the need for better waste retrieval technology.
Waste retrieval equipment has had to be designed to fit into 12-inch-diameter risers that provide access to the tanks, which are large enough to hold as much as 1 million gallons of waste. For as many as 67 of the tanks, little liquid can be added to break up or move the waste because they may have leaked waste in the past.
However, Washington River Protection Solutions is working on a plan to cut larger openings in the tops of the underground tanks, while shielding workers from the high-level radioactive waste inside, to allow more robust equipment to be lowered into the tanks.
That's allowed subcontractor Columbia Energy and Environmental Services of Pasco to explore the use of equipment already used in industry, such as a vacuum technology developed for the mining industry for gold dredging.
Washington River Protection Solutions is developing a robotic arm, called the Mobile Arm Retrieval System, or MARS, that will require a 42-inch diameter riser. The robotic arm is being designed to reach into every cranny of the underground tanks and can be fitted with different attachments -- like a vacuum -- to attack different waste problems.
Vacuum systems have been used to empty some of the smallest underground tanks at Hanford. But the work was very slow even for small quantities of waste -- about 2,000 gallons -- and the vacuums were not powerful enough to pull up the heaviest waste at the bottom of some tanks.
They also required more liquid to be released into the tanks than is optimal for tanks known to have leaked in the past. Solid waste remains in the single-shell tanks -- including sludge with the consistency of peanut butter, hard layers that have to be broken up and coarse sand or gravel -- but pumpable liquids already have been removed.
The new MARS Vacuum Retrieval System being designed and built by Columbia Energy and Environmental Services relies on the venturi effect. Liquid is injected through a system above the waste at 70 gallons per minute and 100 pounds per square inch of pressure, to create a vacuum that pulls up the waste from the floor of the tank.
It's the same concept used to draw fertilizer into a garden hose, said Rob Corbin, MARS test director for Columbia Energy and Environmental Services. But for the tank retrieval system, the liquid used to create a vacuum stays within the system rather than being introduced into the tank.
"I'm pretty happy about how it digs down and gets it out," said Scott Saunders, the tank technology manager for Washington River Protection Solutions. At the demonstration Thursday the vacuum was sucking up both mock sludge and coarse sand.
Nozzles are used to add small amounts of water to make the waste easier to move and other nozzles can be used if a stronger spray is needed to break up hard waste.
The waste is vacuumed about 15 feet up to a holding tank inserted in the larger waste tank. From there a pump is used to move the waste out of the underground tank. In the previous vacuum system, the vacuum had to pull waste up to 45 feet from the bottom of tanks.
The system should be ready in 2012 to use in Tank C-101 and then is planned to be moved to Tank C-105. Both are believed to have leaked in the past and have at least 200,000 gallons each of solid waste.
The new vacuum system is being developed and tested with about $10 million of federal economic stimulus money.
"Its another tool in the toolbox of retrieval," said Nancy Uziemblo, a geologist at the Washington State Department of Ecology, which regulates tank waste retrieval.
* More Hanford news at hanfordnews.com.