The Department of Energy needs to get on with emptying a Hanford double-shell tank leaking radioactive and hazardous waste between its shells, according to the state of Washington.
The state Department of Ecology told DOE in a strongly worded letter sent Thursday that its lack of action is “unacceptable.”
DOE has known that the nuclear reservation’s oldest double-shell tank, AY-102, is leaking waste between its shells for more than a year. But the agency has not pumped any waste from it despite state requirements, according to the letter.
State regulations require DOE to inspect the tank to determine the cause of the leak, including removing as much of the waste as necessary to allow for the inspection, the state said. That is required to be done within 24 hours or as early as possible.
DOE does not know the location of the leak, the rate of leakage or conditions at the leak site within the tank, the state said. It also does not know when or how the leak might worsen or what effect changes in temperature will have on the leak.
“We are deeply disappointed,” the state said about a DOE plan calling for no action to remove waste from the tank until conditions worsen. The 75-foot-diameter tank holds more than 800,000 gallons of waste, most of it liquid and some of it sludge.
The state wants DOE and its contractor, Washington River Protection Solutions, to produce a workable plan by Feb. 15 for pumping waste from Tank AY-102.
The tank is one of 28 double-shell tanks and 149 older single-shell tanks, all underground, that have been used to hold 56 million gallons of radioactive waste from the past production of plutonium for the nation’s nuclear weapons program.
Waste is being emptied from the leak-prone single-shell tanks, some of which date to World War II, and stored in the double-shell tanks until the waste can be treated for disposal. But with delays in building the vitrification plant to treat the waste, the double-shell tanks are nearing capacity.
At least one of the single-shell tanks is leaking waste into the ground and more than 60 are suspected of leaking in the past.
But DOE does not believe that waste in the double-shell tank, Tank AY-102, has breached the outer containment shell to reach the soil.
It characterized the interior leak as “small” in a statement released Friday. This past spring it estimated the leak at 190 to 520 gallons of waste, but said a significant portion of the liquid has evaporated, leaving an estimated 20 to 50 gallons of drying waste between the shells.
DOE has installed a pump that could drain liquid waste from the tank.
However, as long as 151,000 gallons of radioactive sludge remain in that tank, some of the 680,000 gallons of liquid also will need to be left in the tank to help cool it. The sludge generates heat as it radioactively decays, and heat can increase corrosion rates in the tank and contribute to generating potentially flammable hydrogen gas.
The Defense Nuclear Facilities Safety Board has questioned DOE assumptions about pumping out some of the liquid waste, finding there are uncertainties about what a change in temperature, pressure or chemistry would mean to the rate of leaking and to the physical condition of the tank, which is more than 40 years old.
To prepare to also remove sludge from the tank, DOE estimated it needs another 18 to 20 months.
In the meantime DOE continues to monitor the tank. The agency said it does weekly visual surveys and has worked with private industry to develop a robotic crawler that has been sent into the small channels within the tank’s leak detection pit system to collect information.
There are risks to waiting to empty the double-shell tank, according to the state’s letter.
The leak has the potential to clog ventilation channels, undermining the ability to moderate the heat in the tank and leading to greater corrosion of the tank bottom. The outer shell of the tank is thinner than its inner shell.
DOE does not appear to have a plan for what to do if the ventilation channels clog or to predict how long the outer shell will hold, the state said.
The state accepts that DOE was unable to immediately begin pumping waste from the tank when the interior leak was discovered and that some safety issues may need to be resolved to pump the tank.
“However, this does not relieve you from the regulatory requirement to remove it at the earliest practicable time,” the state said. “We cannot support merely waiting for conditions to worsen before taking action.”