Radiation readings that had Hanford officials checking for a possible leak in Hanford’s second oldest double shell tank have returned to normal, Mark Lindholm, president of Hanford tank farm contractor Washington River Protection Solutions (WRPS), said in an update to employees as they were leaving for the Memorial Day weekend holiday Friday.
Checks of the continuous air-monitoring filter paper for the space between Tank AY-101’s double shells, called the annulus, no longer show levels above the historic readings. “It appears the elevated levels detected earlier can be linked to historical contamination of the annulus,” Lindholm said in a message to employees.
Tank farm records show that the annulus has been radiologically contaminated, possibly since as early as 1976, a few years after it was put into service. Abnormally high readings on the filter paper in April caused WRPS to investigate whether the tank was leaking. No waste has been found in the tank’s leak detection pit and video inspections of the annulus show no leak and no changes from videos recorded in 2012, 2013 and 2014. Another video inspection of the annulus is planned in July and weekly checks of the filter paper will continue.
Hanford’s oldest double shell tank AY-102 does have an active leak contained within its shells, with the waste in the 30-inch-wide annulus now stabilized at about 4 to 5 inches deep as waste retrieval from the primary shell is paused, Lindholm said. Waste had been slowly leaking into the tank’s annulus in recent years and drying in puddles. But the rate of leakage increased dramatically as work was done to empty the tank in April.
As the level reached a little more than 5 inches, the lowest point at which pumping is possible, the waste was pumped back into the shell multiple times. Work has now paused to empty the tank to allow better retrieval equipment to be installed in the tank. Enhanced-reach sluicing systems are expected to get closer to waste that now is piled up at the sides of the tank and remove it.
Waste in the center of the tank is estimated to be about 6 inches deep, but at the edge of the tank it is as deep as an estimated 30 inches in places. The switch over of equipment is underway, Lindholm said. In addition, workers are practicing with a mockup system at Hanford’s Cold Test Facility, a full-size, above-ground tank used for retrieval practice and equipment testing with nonradioactive simulants. Although the enhanced-reach sluicing system has been used successfully at Hanford’s single shell tanks, the double shell tanks have more equipment, including air-lift circulators, which sluicing system operators will have to navigate around when retrieval of AY-102 resumes.
