From their grins, you’d think Christmas came early for Hanford officials as they talked Monday about cutting a hole into a massive underground radioactive waste storage tank.
Washington River Protection Solutions, the contractor performing cleanup of the nuclear reservation’s tank farms, bored a 55-inch diameter into the tank through 15-inch-thick concrete and steel rebar over the weekend.
The larger access to the inside of the tank will allow crews to insert a new device into the tank that’s expected to solve the vexing problem of removing solidified wastes from the bottom of the oldest tanks at Hanford.
The cut, the largest-ever cut into an active Department of Energy radioactive waste tank, was made using high-pressure water with a fine garnet grit.
The hole in tank C-107 was then fitted with a riser, or pipe, that will allow the contractor to use a Mobile Arm Retrieval System, or MARS unit, to more quickly and efficiently pump waste from the aging single-shell storage tank to a newer and sturdier double-shell tank, officials said.
“We believe this is a real game-changer for the way waste is retrieved from these tanks,” said Kent Smith, Washington River Protection Solutions’ deputy manager of retrieval and closure operations.
The contractor currently uses a process called modified sluicing to break up solid waste that builds up in the bottom of the old tanks. That process uses high-pressure water to break apart tank sludge, which can range in consistency anywhere from sand to mud to rock.
But modified sluicing has been successful at reaching only about 90 percent of the waste inside the tanks, and it hasn’t been able to break up and move some of the harder wastes.
“We have developed robotic arms at Hanford for many years, but arms that would fit into the tanks through available risers were too small to do the job,” said Chris Kemp, deputy federal project director for DOE’s Office of River Protection in Richland.
That means other techniques have to be used, and those mean added time and expense to clean up the tanks, Smith said.
The MARS unit employs a robotic arm that’s designed to reach every cranny inside the tanks, and should be able to help achieve the goal of removing 99 percent or more of the tank wastes, Smith said.
The unit will first be used in tank C-107, where it is expected to remove about 247,000 gallons of waste starting next summer. 2011
The MARS unit is expected to be delivered and installed in February.
* Michelle Dupler: 582-1543; email@example.com