Waste retrieval from the Hanford Site double-shell tank with an interior leak has been completed to the requirements of a settlement agreement between the Department of Energy and the Washington state Department of Ecology, according to DOE.
The federal agency and Hanford tank farm contractor Washington River Protection Solutions told the state that two technologies had reached all waste that could be extracted from the tank that originally held about 744,000 gallons of material. The settlement required that double-shell Tank AY-102 by March 4 be emptied enough to determine the source of the leak between its shells.
The tank was leaking small amounts of waste from its primary shell into the space between its shells when the settlement agreement was signed in 2014. Disturbing the waste during retrieval caused more waste to flow into the 30-inch-wide space between the shells, but the issue was anticipated and a pump inserted into the space to periodically draw material back into the tank. None of the waste is believed to have breached the outer shell to taint the soil beneath the underground waste storage tank.
WRPS, along with the union umbrella group Hanford Atomic Metal Trades Council (HAMTC), sent a message to tank farm employees Tuesday saying that 98 percent of the waste in the tank had been removed. Workers extracted 725,000 gallons of waste, leaving 19,000 gallons of sludge in the tank when the limits of technology were reached. “Now that waste retrieval is complete, a video inspection of the leak site(s) will be conducted as conditions allow,” the message said. “Follow-up activities to further investigate or implement additional retrieval will be planned and executed based on the result of the video inspection and conceptual design evaluation.”
Hanford’s tank farm holds roughly 56 million gallons of chemical and radioactive waste that was a byproduct of Cold War-era plutonium production for the U.S. nuclear arsenal.
Tank AY-102, which has held waste since about 1970, is the oldest double-shell tank at Hanford and had documented construction problems. DOE has not ruled out repairing the tank and returning it to service, although officials have said that is unlikely.
Hanford officials already have an idea of where the leak is occurring, after noting that more waste would flow into the space between the shells when material was disturbed in one area of the tank. Learning more about the source of the leak might help officials understand the condition of the remaining 27 double-shell tanks still being used to store waste removed from single-shell tanks until it can be treated for disposal.
Preparing Tank AY-102 for waste retrieval required more than two years of infrastructures on both Tank AY-102 and the sturdier double-shell tank that now holds its sludge waste, Tank AP-102. Some of the construction was high risk, including using long-reach tools to safely remove five obsolete pumps contaminated with tank waste, according to the employee message signed by WRPS President Mark Lindholm and HAMTC President Dave Molnaa.
Waste retrieval operations began on March 3, 2016, one day ahead of the deadline set by the settlement agreement. Liquid waste had been pumped out and transferred to double-shell Tank AW-105 by the next month. Removal of the 151,000 gallons of sludge that remained started with two standard sluicers, the same technology that has been used for years to remove waste from Hanford’s leak-prone single-shell tanks. The sluicers use a jet of recycled liquid to dissolve and move waste toward a pump for removal from the tank.
Hanford officials knew that as retrieval advanced deeper into the tank it would become more difficult and prepared four enhanced-reach sluicers to replace the first technology. Work with the enhanced-reach sluicers, which can reach more areas of the tank and are equipped with an additional high-pressure spray system, began in December when about 40,000 gallons of sludge remained. Work halted around mid-February as the enhanced-reach sluicers were no longer able to collect much waste from the tank.
Kevin Smith, manager of the DOE Office of River Protection, said in a statement Tuesday that “WRPS did an exceptional job planning, coordinating, and executing this work. I’m very proud of them for meeting the schedule commitment under challenging conditions, including our unpredictable winter weather.”
Lindholm and Molnaa said in their message to workers that the project “captures how critical work can be accomplished safely and effectively when labor and management work together to resolve our issues and concerns.” They said workers represented by HAMTC and the Building Trades worked alongside nonunion counterparts “to overcome a series of obstacles and challenges to meet this important requirement. The team completed the work safely, overcoming the challenges of extreme weather and industrial, radiological and chemical vapor hazards.”
