A visual inspection of the Hanford Site’s oldest double-shell waste tank has found at least seven leaks from the inner shell.
The Department of Energy confirmed in 2012 that Tank AY-102 had a slow leak from its inner shell into the space between its shells. No waste is believed to have breached the outer shell to contaminate the environment.
Multiple visual inspections were performed between April and October 2017 after tank farm contractor Washington River Protection Solutions emptied all but about 19,000 gallons of waste from Tank AY-102, which has a capacity of 1 million gallons. A DOE settlement agreement with the Washington state Department of Ecology required the tank to be emptied enough for an inspection to be conducted.
Workers used video cameras inside the enclosed, underground tank and initially found two spots with bubbles that indicated leaks along the weld lines visible at the bottom of the inner shell, Glyn Trenchard, DOE’s assistant manager of the tank farms, said Wednesday at a Hanford Advisory Board meeting in Richland, Wash. The leaks were near the point at which four plates were welded together.
Through use of high-definition video cameras, corrosion and pitting could be seen on the bottom of the inner shell. When a small amount of liquid from the space between the shells was added to the inner shell, it could be seen disappearing through five pits on the floor, Trenchard said. The chemistry of the waste in the carbon steel tank was not well controlled when the tank went into service in 1971, which could have contributed to the corrosion.
The Energy Department, which has 60 days to complete an inspection report, will discuss options with the Department of Ecology. When retrieval of the waste began, there was some discussion that determining the site and cause of leakage in the inner shell might allow the tank to be repaired and returned to service, although some officials said that was unlikely.
The results of the inspection could provide useful information for managing Hanford’s other tanks, which hold 56 million gallons of chemical and radioactive waste produced during decades of plutonium production for the U.S. nuclear deterrent, Trenchard said. Hanford has 149 leak-prone single-shell tanks. Their waste is being emptied into newer double-shell tanks for storage until the material can be treated for disposal. With Tank AY-102 taken out of service, 27 double-shell tanks remain in use.
