Hanford workers removed another 5,500 gallons of radioactive waste over the weekend from the nuclear reservation’s double-shell tank with an interior leak.
Leaked waste also was pumped from the space between the tank’s shells several times, but there continues to be no evidence that waste has breached the outer shell of the tank to reach the environment.
After the weekend’s pumping, about 41,000 gallons of the original 151,000 gallons of sludge are left in the primary shell of the tank, according to Jerry Holloway, spokesman for Washington River Protection Solutions, the Department of Energy contractor managing Hanford’s waste storage tanks.
In the center of the tank being pumped, Tank AY-102, some of the waste has been reduced to about six inches deep, but the level is uneven and at the edges of the 1-million-gallon-capacity tank, the waste is 20 to 30 inches deep in places.
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Workers may not be able to get enough waste out of the tank to determine what caused the leak without installing a better waste retrieval system, despite the substantial progress made to remove sludge from the tank in less than a month. The sludge is being transferred to one of Hanford’s other 27 double-shell tanks to be stored until it can be treated at the Hanford vitrification plant and then disposed of in a stable glass form.
Washington River Protection Solutions has been using a sluicing system that sprays liquid waste on the sludge to dissolve it and move it toward a pump for removal.
The sluicing system now in the tank may have to be traded out for one that can reach to more areas of the tank.
Original plans for the retrieval of waste for Tank AY-102 called for trading out the sluicing system in late spring or summer for a newer extended-reach sluicing system that can fold out to reach more areas. The extended reach sluicers also are equipped with a high pressure water system that can be used to break up any hardened waste.
Work had stopped Monday on the tank to troubleshoot a pump in a double-shell tank that is supplying the liquid waste for the sluicing system in Tank AY-102. Using liquid waste rather than water cuts down on the amount of additional waste created during work to retrieve waste.
Hanford workers had removed about 95 percent of the waste from the tank, which included liquid waste sitting above the sludge, when an alarm sounded April 17, alerting workers that the rate of leaking into the space between the tanks had increased significantly.
It was a known risk and a pump had been inserted into the space between the shells before waste retrieval started.
Waste was being retrieved from the tank because about 70 gallons of waste had leaked from the inner shell over several years. On April 17 an estimated 3,000 to 3,500 gallons leaked into the space between the shells.
The Department of Energy has a deadline of March 4, 2017, under a settlement agreement with the state of Washington to have the tank emptied enough to investigate the cause of the leak.