More evidence was discovered this week that might indicate that one of Hanford's double-shell tanks is deteriorating.
In early August, radioactive material was found between the inner and outer walls of an underground tank at Hanford for the first time, raising concerns that waste may be leaking out of the inner shell of the tank.
This week, more unusual material was found when a video camera inspected another part of the area between the inner and outer walls of Tank AY-102.
It was the first additional area of the tank checked as an investigation was launched.
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A photo of the same area between the two shells of the tank in 2006 showed it was clean six years ago.
"We just have got to think it's not encouraging to find another spot that clearly was not there in 2006," said Cheryl Whalen, cleanup section manager for the Department of Ecology's Nuclear Waste Program.
The state is the regulator of the tank waste, which includes 56 million gallons left from the past production of weapons plutonium and stored in underground tanks at Hanford.
Waste is being emptied from 149 single shell tanks, many of which have leaked waste into the soil in the past, into 28 newer double-shell tanks. The waste is intended to be held there until the last of it can be treated for disposal about 40 years from now.
Suspicions were raised in early August that the inner shell of Tank AY-102 might be leaking when a video camera lowered into the space between the inner and outer shells of the tank and then a video camera lowered for a more in-depth look found unexpected material there.
The cameras showed two side-by-side areas of contamination, one a dry mound about 24-by-36-by-8 inches. A sample of the material was collected, showing it was radioactive.
The Department of Energy launched an investigation then, with plans to send cameras down the 10 risers that allow access from above ground into the space between the tank's shells. The area around the first additional riser checked this week turned up the third spot of material.
It has not been determined yet if the material is radioactive, said Lori Gamache, DOE spokeswoman.
"We are continuing our investigation, including gathering additional information from other tank risers," DOE said in a message to workers Friday.
The state is waiting for more information, Whalen said. The material found between the tank shells may not be the result of a leak, but something odd is happening, she said.
DOE also is investigating whether the radioactive material may have come from a pit with pumps or piping serving the AY Tank Farm where there could have been a spill.
Tank AY-102 went into service in 1971 and is just past its design life of 40 years.
It has a capacity of about 1 million gallons of waste, but currently stores about 707,000 gallons of liquid waste and 151,000 gallons of waste sludge.
Initially, work is being done to figure out how radioactive material ended up outside the inner shell of Tank AY-102. 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.
None of the waste has leaked outside the outer shell of Tank AY-102 to contaminate the soil and the radioactive material found between its shells presents no risk now to the public, workers or the environment, according to DOE.
"This is the first tank to show signs of aging," said DOE in an initial message to employees last week. "Events such as this reinforce the importance of safely emptying all the Hanford waste storage tanks as quickly as possible and convert the waste into a stable form for safe, long-term storage."