A large robotic arm has begun retrieving radioactive waste from one of Hanford's underground tanks, raising hopes that the slow and difficult work to empty tanks will become more efficient.
"We believe this new system will be a game changer for us and allow us to move more waste out of our tanks faster and at less cost," said Kent Smith, the tank retrieval manager for Department of Energy contractor Washington River Protection Solutions, in a statement.
The Mobile Arm Retrieval System, or MARS, already has changed how work is done at the Hanford tank farms, after Hanford workers cut the largest hole ever in a U.S. radioactive waste tank to install the system in December.
Workers must empty radioactive waste from 142 leak-prone single-shell tanks into newer double-shell tanks until it can be treated for disposal when the Hanford vitrification plant begins operating. The nuclear reservation has 56 million gallons of waste stored in underground tanks.
Until now, waste has been retrieved from the enclosed underground tanks with equipment that could fit down 12-inch diameter risers to reach aging tanks not designed for waste removal. Often retrieval equipment could pull out only some of the waste, leaving a hard layer of waste at the bottom of the tank.
But when Washington River Protection Solutions won the Hanford tank farm contract in 2008, it said it planned to develop a robotic arm capable of using different technologies to go after different types of waste. Tanks may have sludge the consistency of peanut butter, a heavy sand- or gravel-like material and a hard layer of waste comparable to low-strength concrete that has to be broken up.
When the contractor couldn't develop a strong enough robotic arm that still would fit through the existing risers, it proposed cutting an opening into tanks to install risers wide enough for much larger and more robust equipment.
In December, it used remotely operated equipment to cut a 55-inch hole into the top of Tank C-107 and then installed a 42-inch diameter riser, showing that opening a high-level radioactive waste tank could be carefully done without harming workers or the environment.
The 25-foot mast and robotic arm of MARS were inserted into the tank in June, and crews then made the piping, hydraulic and electrical connections to allow the system to begin operating.
During the past few days, the components of MARS in Tank C-107 were tested, and sustained retrieval of waste began Tuesday.
Hanford officials expect that MARS not only will allow just one set of equipment to be inserted in the tank to retrieve all consistencies of waste, but that it also will move the waste faster.
Just seven of 149 single-shell tanks have been emptied so far at a rate averaging fewer than one completed a year. Legal deadlines already have been extended for when tanks are required to be emptied, and the latest deadline under a court-ordered consent decree requires DOE to have all 16 tanks in the group called C Tank Farm emptied by 2014. Six of the tanks emptied so far are in C Tank Farm.
"It is vital that we continue to meet our regulatory commitments for tank waste cleanup at Hanford," Joanne Norton, DOE project director for tank waste retrieval, said in a statement. The MARS technology shows great promise to help meet the 2014 deadline, she said.
During earlier testing with nonradioactive material, MARS was able to efficiently retrieve waste with 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.
The robotic arm can be raised or lowered in the tank, rotated 360 degrees and unfolded and lengthened to reach 40 feet to the tank sides or bottom. The operating head, with multiple low- and high-pressure spray nozzles, is articulating, allowing it to reach around obstructions encountered in the tank.
Tank C-107 was picked for the first use of MARS because it is not known to have leaked in the past. The MARS attachments can use water, but in Tank C-107 are using liquid waste from nearby tanks to avoid creating more radioactive waste that must be stored and then treated for disposal.
A vacuum version of MARS is being tested for use in tanks believed to have leaked in the past. It will use a minimum amount of liquid to mobilize the waste and will remove the liquid almost as fast as it is introduced into a tank.
Tank C-107 has a 530,000-gallon capacity and was built in 1943, making it one of the oldest waste storage tanks at Hanford. When MARS started work, it had about 253,000 gallons of waste, most of it sludge but with some hard material similar to rock or gravel.
"It's been a long process to achieve one of the state's highest priorities -- removing waste from single-shell tanks to protect our environment," Nancy Uziemblo, of the Washington State Department of Ecology, said in a statement. "We are counting on the MARS to jump-start single-shell tank retrievals."
