Radioactive material has been found between the inner and outer walls of an underground double-shell tank at Hanford for the first time.
The discovery increases the concern that the inner shell of the tank may have leaked, indicating the deterioration of at least one of the 28 double-shell tanks that are needed to hold millions of gallons of waste for decades to come.
"If we determine there was a leak or a previous spill, it reinforces the urgency of emptying the tanks and completing the mission," said Tom Fletcher, Department of Energy assistant manager of the tank farms. "The tanks are not getting any younger."
Hanford has 149 leak-prone single-shell waste tanks that are being emptied into the newer double-shell tanks. The waste is planned to be held there until the vitrification plant under construction can treat the waste for disposal, with the tanks required to be emptied by 2052.
"This changes everything," said Tom Carpenter, executive director of Hanford Challenge. "These tanks were supposed to last another 40 years, but that thinking has been superseded by this new reality."
DOE notified its regulator, the state Department of Ecology, of the issue last week, but it did not become public knowledge until Friday after Hanford Challenge obtained an email sent by DOE to the state.
The Department of Energy has not confirmed what the material is or where it came from, Fletcher said. DOE is investigating to determine whether waste leaked out of the inner shell of Tank AY-102 or the material came from another source, such as cross contamination from a pit with pumps or piping serving the AY Tank Farm where there could have been a spill.
It was discovered during video monitoring of the area between the inner and outer walls that was designed as an overflow space if the inner steel liner were to leak. A video camera was inserted down a tank riser that had not previously been used for visual examinations.
The video showed two side-by-side areas of contamination. One was a dry mound about 24 by 36 by 8 inches.
There was no contamination on the camera when it was removed, but a sample collected Aug. 10 showed the material was radioactive.
"This is fixed contamination on the floor. There is no liquid. There is no vapor," Fletcher said.
It presents no risk now to the public, workers or the environment, he said.
Tank AY-102 has a capacity of about 1 million gallons of waste but currently stores about 707,000 gallons of liquid waste and 151,000 of waste sludge. In total, the 177 underground tanks at Hanford hold 56 million gallons of radioactive and hazardous chemical waste from the past processing of irradiated fuel to separate out plutonium for the nation's nuclear weapons program during World War II and the Cold War.
Tank AY-102, which went into service in 1971, is just past its designed service life of 40 years.
When the state was notified last week, it assumed there was some water in the space between the two tanks. DOE said there have been small amounts of water in the space in the past from rinsing monitoring equipment.
The news from DOE that the material was radioactive came as a surprise, said Cheryl Whalen, cleanup section manager for the Department of Ecology's Nuclear Waste Program.
"We're concerned," she said. "If anything happens to the DST's (double-shell tanks), it will be a difficult situation because we are very dependent on all the tanks for single-shell tank retrieval."
If there is a leak in the inner shell of the tank, it is a slow leak, she said.
DOE's first step in its investigation is creating a historical timeline for the tank to determine what events, including in pits, could have affected it, Fletcher said.
Hanford workers have increased monitoring to make sure there is no change in conditions during the investigation. Cameras are being sent down twice a week, and the level in the tank will be checked every shift to make sure there is no indication of liquid leaking out of the inner shell. Samples also will be taken from both of the places that appear to have material between the inner and outer tanks.
Work is then planned to inspect all areas that are accessible between the inner and outer shells and to check to confirm no waste has made its way out of the outer shell.
Longer term, work will be done to determine if other double-shell tanks might also have similar issues and to explore ways to remove the material from between the shells, Fletcher said.