No more evidence to suggest leak in Hanford Tank AY-101

Evidence continues to mount that Hanford’s second oldest double-shell tank holding radioactive waste is not leaking, according to Hanford officials.

An unusual, elevated radiation reading in April triggered an investigation to see if Tank AY-101 was leaking waste into the space between its shells, just like Hanford’s oldest double-shell tank.

“It appears the elevated levels detected earlier can be linked to historical contamination of the annulus,” Mark Lindholm, project manager for Washington River Protection Solutions, the Hanford tank farm contractor, said in a message to employees as they left for the holiday weekend. The annulus is the 30-inch-wide space between the tank’s shells.

Concerns had been raised when filter paper in the ventilation system for that space showed radiation levels above the normal level.

Weekly checks of the filter paper collected from the system show radiological readings have returned to the historical level, Lindholm said.

The filter paper will continue to be checked weekly and another video inspection of the space is planned in July. Initial inspections since the elevated radiation reading have found no waste in the annulus. The video shows the space looking just as it has in other inspections in other recent years.

In addition, no waste has been found in the tank’s leak detection pit.

The tank had radioactive contamination in its annulus as long ago as 1976, according to Hanford officials. The tank currently holds 995,000 gallons of radioactive waste.

At Hanford’s oldest double-shell tank, Tank AY-102, the level of waste in the 30-foot-tall annulus has stabilized at 4 to 5 inches deep, Lindholm said.

The tank had been known to have waste slowly leaking into its annulus and drying there in patches for several years, but the rate of leakage increased dramatically in April as radioactive sludge was being removed from the tank.

Workers had to keep pumping waste from the annulus back into the inner tank as work to empty the tank continued. The waste can be pumped when it reaches a little more than 5 inches deep.

Under a settlement agreement with the state of Washington, the Department of Energy and its tank farm contractor must have the tank emptied to determine the cause of the leak by next spring.

Work to remove sludge is paused now — allowing the waste level in the annulus to stabilize — as a more efficient waste retrieval system is installed.

An enhanced sluicing system will allow retrieval of hard-to-reach waste, including waste built up at the sides of the tank.

Workers are practicing with a mockup of the equipment of the Cold Test Facility. Although they have experience using the enhanced reach sluicing systems to remove waste from Hanford’s older single-shell tanks, the newer double shell tanks have air lift circulators that the system has to maneuver around.

This story was originally published May 27, 2016 at 5:16 PM with the headline "No more evidence to suggest leak in Hanford Tank AY-101."