The Department of Energy has begun to take some action on the Hanford tank that is believed to be leaking radioactive waste into the soil beneath it.
A portable exhauster is being used to reduce the volume of liquid in the tank that could leak. It also could reduce the rate at which waste is leaking into the ground.
The exhauster has removed about 2,000 gallons of water from Tank T-111, according to Washington River Protection Solutions, the Department of Energy contractor that manages Hanford’s underground waste storage tanks. The tank holds about 436,000 gallons of radioactive waste in the form of sludge.
“The exhauster is performing as we hoped it would,” said Mark Lindholm, the acting president of the tank farm contractor, in a statement. “This is an important step in the right direction as we try to minimize liquid inside T-111.”
The tank is leaking waste at the rate of about 1.8 gallons per day, down from as much as 3.1 gallons a day in spring 2013, according to a Hanford report issued last year..
DOE announced in February 2013 that the tank, which was built during World War II, had a declining level of waste and appeared to be leaking. It was the first of Hanford’s 149 single-shell tanks believed to be leaking after DOE completed a project to empty pumpable liquids from the aging tanks.
“DOE and Ecology agreed there was a reason to address the declining level and leak” in Tank T-111, said Jeff Lyon of the Washington State Department of Ecology, a regulator for the Hanford tanks. “They voluntarily decided to implement the technology.”
The tank had an estimated 2,500 to 4,000 gallons of liquid sitting on top of the sludge when evaporation began. Initially, a 30-day test was conducted, removing the first 1,000 gallons of liquid. Since Sept. 28 about that much liquid has been removed again.
Washington River Protection Solutions said the liquid can be evaporated at a rate of 25 to 30 gallons a day.
Cameras inside the tank show a change in the amount of liquid pooled on top of the sludge, according to the tank farm contractor. It expects the exhauster to remove the pooled liquid plus dry out the top few inches of the sludge.
The tank was suspected of leaking in 1974 and a pump was used to remove as much liquid as possible then and again in 1995. Since then the level of waste has dropped at times and increased at other times, believed to be the combined effects of waste leaking from the tank and precipitation finding its way in.
An average of 130 gallons of water a year may have found its way into the tank, although that likely has varied during the years. The current leak period appears to have begun in 2000 to 2003 or possibly earlier, according to the 2014 report.
Water may have leaked into the tank from an underground concrete pit covered with a removable concrete block that was used to pump waste into the tank when Hanford was producing plutonium for the nation’s nuclear weapons program.
The intrusion of precipitation into the tank may have masked the liquid waste leaking out of the tank when readings of waste volume were made, the state has said.
Exhausters have been used previously to evaporate some of the liquid from single-shell tanks, but this is the first exhauster system Washington River Protection Solutions has used to address precipitation that has gotten into a tank, according to the tank farm contractor.
The pooled water is suspected to be a combination of water getting into the tank and liquid remaining trapped among the waste when pumping stopped.
Washington River Protection Solutions said the tank has about 38,000 gallons of liquid throughout the sludge and resting in the layer on top of it.
Reducing the water at the top of the waste should remove some pressure on the liquid below it and should reduce the rate of leaking, said state and tank farm contractor officials.
Washington River Protection Solutions is considering using an exhauster to evaporate liquid in more than two dozen other single-shell tanks with liquid pooled on top of the waste.
“We think it’s a great project for that,” Lyon said.
The exhauster was moved to the T Tank Farm last year and parts were fabricated over the winter to allow it to be installed at Tank T-111. In operation the system vents water vapor after particulates have been trapped in filters.
“Evaporation using active ventilation costs a small fraction of new pumping technologies,” Lindholm said.
It also requires less labor than using a pump to remove liquid and the liquid does not have to be stored in Hanford’s newer double-shell tanks, which are used to hold waste emptied from single-shell tanks until it can be treated for disposal.