Just one of six suspect tanks at Hanford is leaking radioactive waste into the ground, according to evaluations released Wednesday by the Department of Energy.
However, the Washington State Department of Ecology does not agree with all of the conclusions in the reports. The good news is that both DOE and the state agree that four of the six tanks in question are not leaking, said Dieter Bohrmann, a spokesman for the Department of Ecology.
In the past, 67 of 149 single-shell tanks at Hanford were suspected of leaking radioactive and hazardous chemical waste into the ground. But the underground tanks were believed to be stable after the last of the pumpable liquids was transferred to newer double-shell tanks by 2004, leaving mostly solids in the single-shell tanks.
That assumption changed Feb. 15 when Washington Gov. Jay Inslee received new information from then-Energy Secretary Steven Chu. He said Tank T-111 was leaking up to 300 gallons a year of waste into the ground in central Hanford. The waste is left from the past production of plutonium for the nation’s nuclear weapons program.
The evaluation released Wednesday concluded that Tank T-111 is leaking. But DOE also said that the rate at which it is leaking appears to be decreasing.
A week after Inslee learned the tank was leaking, Chu informed the state that five more underground, single-shell tanks also appeared to be leaking.
The new evaluation concluded that changes in the level of liquid in those five tanks could be attributed to evaporation. The rate of evaporation in those tanks exceeded the calculated loss of waste, according to DOE.
The tanks are passively ventilated through filters and the amount of evaporation depends on factors such as the temperature of the waste, humidity and how much of the liquid remaining in the waste is pooled on top of the waste or is in pockets within the solid portion of the waste.
Four of the suspect tanks — tanks T-203, T-204, B-203 and B-204 — have a capacity of just 55,000 gallons, making them the smallest model of underground single-shell storage tanks at Hanford. They had each been suspected of leaking waste at a rate of about 15 gallons a year.
The fifth tank DOE believes is not leaking but is losing liquid to evaporation, Tank TY-105, is much larger with a capacity of 758,000 gallons. It had been suspected of leaking at a rate of about 150 gallons a year.
The state of Washington agrees that Tank T-111 is leaking and that the four smaller tanks are not leaking.
But DOE and its contractor, Washington River Protection Solutions, have not proven to the state’s satisfaction that the entire decrease in the amount of waste in Tank TY-105 is due to evaporation, said Nancy Uziemblo, a state specialist on retrieving waste from single-shell tanks.
The state also does not agree that the leak from Tank T-111 is slowing. Any leveling off in the rate of leakage has been short term and the tank continues to lose waste, said Jeff Lyon, the state’s tank waste storage project manager.
That at least one of the tanks is actively leaking is a wake-up call, Bohrmann said.
“Some of the tanks need to be revisited to look at their liquid waste content,” Uziemblo said. “They’re not as dry as we think they are.” Some single-shell tanks still have about 50,000 gallons of drainable liquid, despite the earlier work to pump liquid into newer double-shell tanks, Lyon said.
The state wants DOE to either further reduce the amount of liquid waste in some tanks, including tanks T-111 and TY-105, or put a protective cover over the ground above them. The cover doesn’t stop tanks from leaking, but keeps precipitation and snow runoff from carrying leaked waste deeper into the soil.
The amount of liquid waste within the tanks could be reduced by boosting the rate of evaporation or by more pumping, Uziemblo said. However, DOE is looking again at a past proposal to send waste from Tank T-111 and up to 10 more single-shell tanks to the Waste Isolation Pilot Plant, a national repository in New Mexico. The state is concerned that under that proposal Tank T-111 might not be emptied for five years or longer.
Waste that comes from the chemical separation of plutonium from irradiated uranium fuel rods is legally classified as high-level waste, which the New Mexico repository does not accept. DOE would have to show that the waste in the selected tanks was never high-level waste and then confirm it was transuranic waste — typically waste contaminated with plutonium — and could be packaged for shipment to the New Mexico repository.
DOE believes a case could be made that that waste in the 11 tanks comes only from a process to removing the outer cladding from the irradiated fuel or from a process used at two early plants to purify plutonium after it had been separated from other radioisotopes.
DOE raised concerns about whether some single-shell tanks were leaking in 2011 after 20 tanks were identified that appeared to be losing more than 1 inch of waste over 15 years. The study then focused in on the six tanks of most concern, those that were identified as possible leakers earlier this year.
“We will continue to keep the state of Washington, Congress and other key stakeholders apprised of the situation as we continue to monitor the liquid levels inside the single-shell tanks,” DOE said in a statement.
Underground tank leaks in central Hanford do not present an immediate threat to public health, according to the state. The nuclear reservation covers 586 square miles.
But long-term, leaks pose a threat to groundwater and the deeper the contamination goes into the soil, the harder it is to remediate, said Cheryl Whalen, the state’s tank waste cleanup section manager.
“The larger threat is the waste already in the soil and groundwater,” Bohrmann said. “It’s the reason we want to stop anymore waste from getting there.”
Past leaks, plus spills, have released an estimated 1 million gallons of tank waste into the soil in central Hanford.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews