REMOTE-CONTROLLED WATER JET CUTS ACCESS HOLE IN RADIOACTIVE STORAGE TANK
Richland, WA - Water jet contractor AK Services made history recently by cutting the largest-ever access hole in an active US Department of Energy radioactive waste storage tank at the DOE's Hanford Site in southeastern Washington state.
Richland, WA – Water jet contractor AK Services made history recently by cutting the largest-ever access hole in an active US Department of Energy radioactive waste storage tank at the DOE’s Hanford Site in southeastern Washington state.
The Boston-area water jet contractor cut a 55-in. diameter hole in the top of the underground tank to allow for the installation of a robotic system that will remove 247,000 gallons of radioactive and chemical waste stored in the tank during the Manhattan Project and Cold War so it can be vitrified for safer storage.
Battling freezing temperatures and the challenges of running remote-controlled ultra-high-pressure water jet equipment from a 300-ft distance, AK Services used a specially engineered abrasive water jet cutting machine to make the huge cut through 15 in. of concrete and steel rebar in just 22 hours.
It performed the cut at 8 in. per hour using an abrasive jet of garnet grit mixed with 3 gals. per minute of water pressurized to 48,000 psi with a Jet Edge water jet intensifier pump.
AK Services engineered a three-piece stainless steel motion system with two circles separated by guide bushings with a ring gear in the middle. The ring gear featured four redundant Jet Edge High Flow Abrasivejet cutting heads in case of failure and was driven by a set of reduction gears and a drive motor to achieve the proper cutting rate. Pneumatically actuated rams were placed on the sides and bottom to level and secure the system.
“The biggest challenge was running the equipment from 300 ft away,” said Carl Franson, AK Services vice-president of operations. “The tank top is in a radiation area and entry to the area is regulated to the extent that anything that enters the tank farm must be scanned and cleared prior to being released out of the fenced-in restricted area. The pumps and control systems had to be outside of the restricted area to ensure they did not become contaminated with radiation and then become the property of the DOE.
“We also had the added challenge of winter weather, so we installed air dryers and used air-line antifreeze to keep the system from freezing up.”
After the concrete plug was lifted from the tank, it was immediately wrapped in a plastic sleeve to prevent the spread of contamination and then was placed in an isolated area where it is being staged for disposal at the Hanford Site.
The tank is one of more than 100 similar underground tanks that the DOE is cleaning out as part of its environmental cleanup effort at the Hanford Site, which was once home to nine nuclear reactors that produced plutonium for the Manahattan Project and the US nuclear arsenal. Hanford is considered the most contaminated nuclear site in the US.