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HANFORD The toughest and most versatile system engineers have devised to pull radioactive waste out of Hanford's underground tanks is showing promise in tests.
But the robotic arm, planned to reach every cranny of 1 million-gallon tanks, also is the largest system developed to date.
In a major departure from the past attempts to empty Hanford's 149 leak-prone single-shell tanks, this system is too large to fit down the risers with 12-inch openings that provide access to the enclosed tanks.
Instead, a 52-inch hole will have to be cut in the top of the tanks to install a new riser with a 42-inch diameter while shielding workers from the high-level radioactive waste held in the tanks.
"This is transformational technology," which fits in with high-level Department of Energy instructions to look for new technologies rather than making incremental improvements on existing technologies, said Scott Saunders, retrieval technology and systems planning manager for DOE contractor Washington River Protection Solutions.
The robotic arm, called the Mobile Arm Retrieval System, or MARS, is installed at the Hanford Cold Test Facility, an above-ground mock-up of a waste tank. It makes some of the other waste-retrieval technologies previously developed to fit down 12-inch risers, such as robots that roam around the bottom of tanks, look downright dainty.
A mast is inserted from the top of the tank to its bottom with a carriage that can be raised or lowered to position a telescoping arm that can rotate 360 degrees. When it unfolds and lengthens, it can reach 40 feet total. Not only does it have an "elbow" midway to make it more flexible, but the "wrist" above the collection of the tools it holds also can move.
The tools include a water cannon, high pressure nozzles and fan nozzles, each adding options to break up waste or sweep it toward a pump at the bottom of the mast. Once at the pump, more nozzles help break up the waste to make sure it's small enough to be pumped up the mast and out of the tank.
At the Cold Test Facility, the robotic arm has been able to break up and move substances that mimic the three types of actual radioactive tank waste that give Hanford workers trouble. Tanks may have a hard layer of waste, comparable to low-strength concrete, that has to be broken up, plus sludge the consistency of peanut butter and a heavy sand- or gravel-like material.
"In every case MARS has met or exceeded expectations," Saunders said.
Depending on the type of waste, it's projected to remove waste at rates that range from 85 gallons per hour up to nearly 1,000 gallons per hour.
In work to empty the first seven Hanford tanks of solids since 2003, up to four technologies have had to be inserted into each tank.
One commonly used method, modified sluicing, sprayed water from two nozzles at the top of the tank but wasn't good at breaking up and moving the hard heel of waste in some tanks, said Steve Pfaff, DOE project director for tank waste retrieval.
In some tanks, previously developed technology has not been capable of emptying tanks to the goal of 1 percent of waste remaining as a residual at their bottoms. It's also been expensive, with removing the last 15 percent of the waste in some tanks estimated to cost as much or more as removing the first 85 percent.
"Anything we do at Hanford is difficult. It's radioactive," said Nancy Uziemblo, a geologist at the Washington State Department of Ecology, which regulates tank waste retrieval.
But the Department of Ecology is encouraged by the results of testing the robotic arm, she said. It's robust and a single robotic arm may be able to be reused in several tanks, she said.
The robotic arm cost about $10 million to develop, but additional robotic arms are expected to cost $5 million to $6 million.
Washington River Protection Solutions explored ways to create a strong and versatile arm that would fit through a 12-foot riser, but it wasn't feasible, Saunders said. "Making the move to cut a larger hole was a key enabler," he said.
Although creating a larger opening in the top of the tank will increase risk to workers, the arm is intended to be versatile enough to eliminate the need to have to keep inserting different types of systems into the tank. That also creates a risk to workers, officials said.
Next, the contractor plans to try adding a liquid vacuum system to the robotic arm at the Cold Test Facility. Because some tanks are suspected of leaking, workers cannot add much liquid to them to retrieve solids. Having a system that can be efficiently and safely used in suspected leakers is critical to Hanford cleanup.
As that work continues, Washington River Protection Solutions is making plans to empty Tank C-107, which is not believed to have leaked, with the robotic arm now being tested. It could go into the tank at the end of 2010 and be operating in 2011.
-- Annette Cary: 509-582-1533; acary@tricityherald.com
