Hanford workers have evaporated enough excess water from radioactive waste in underground tanks to free up space nearly equivalent to a new tank.

Washington River Protection Solutions removed 940,000 gallons of condensate from two double-shell tanks with the nuclear reservation's 242-A Evaporator in work completed last week.

The Department of Energy contractor is emptying waste from leak-prone single-shell tanks into newer and sturdier double-shell tanks to be stored until the waste can be processed for disposal at the vitrification plant.

Space is at a premium in the double-shell tanks. Hanford has about 53 million gallons of radioactive waste stored in underground tanks, and the double-shell tanks can hold just 28 million gallons of waste.

"It's our job to make storage space in the double-shell tanks," Rebecca Raven, the 242-A Facility Operations manager for WRPS, said in a statement. "Without the evaporator, we have no storage space and without storage space we can't retrieve waste from the old single-shell tanks."

The evaporator usually is operated twice a year, but this was the first evaporator run since 2007.

Campaigns were temporarily suspended to allow a series of upgrades to the 32-year-old evaporator that included modernizing the ventilation system, updating the monitoring and control system, rebuilding one of the two main pumps and decontaminating the condenser room.

In the evaporator, liquid tank waste is heated under vacuum so it will evaporate at a temperature of about 125 degrees. Water vapor from the heated waste is captured, condensed, filtered and sent to the nearby Liquid Effluent Retention Facility for further treatment and then disposal. The concentrated waste is returned to the double-shell tanks.

Since the 242-A Evaporator began operating in 1977, it has reduced the total volume of waste by about 67 million gallons. That helps avoid the high cost of building new double-shell waste storage tanks, according to WRPS.

Liquid has to be added to the waste for some of the techniques used to empty single-shell tanks and liquid also is needed to thin some of the waste enough to allow it to be pumped from tank to tank.