A video inspection of Hanford's oldest double-shell tanks holding radioactive waste is finished with no more leaks found.
Hanford's oldest double-shell tank, Tank AY-102, was discovered to have a leak from its inner shell in October, prompting concerns about the soundness of all of Hanford's 28 double-shell tanks.
The Department of Energy responded with a plan for video inspections of the six additional double-shell tanks that began holding waste in the '70s. Video cameras were lowered down risers that extend from the surface of the ground into the space between the shells of the six tanks to check for leaks.
"No leaks found in these six tanks is good news for the department," said DOE spokeswoman Lori Gamache. "These visual inspections confirm the integrity of these tanks and provide us with a baseline for future assessments."
The underground tanks were planned to last 40 years, and the oldest two double-shell tanks now have held waste for longer.
The two tanks in the AY Tank Farm, including the one with the interior leak, began holding waste in 1970. The two tanks in the AZ Tank Farm went into service in 1974, and the three tanks in the SY-Tank Farm went into service in 1976.
"Ecology is pleased that the inspections are complete and that the findings indicate that these (six) tanks remain compliant with state regulations," a statement from the Washington State Department of Ecology said Tuesday. "The state will continue to work with DOE and the contractor to monitor the integrity of the other double-shell tanks."
The state is the regulator for Hanford's waste tanks.
Not only do the seven tanks that went into service in the '70s have similar construction, they also had similar operating histories, said John Britton, spokesman for Washington River Protection Solutions.
Hanford's double-shell tanks are being used to hold waste emptied from Hanford's older, leak-prone single-shell tanks, some of which date from World War II. Hanford began producing plutonium then for the nation's nuclear weapons program.
The double-shell tanks are nearing capacity as the need to empty single-shell tanks becomes more urgent.
Six single-shell tanks were recently discovered to be leaking radioactive waste into the ground, and DOE continues to look at another 14 single-shell tanks.
The double-shell tanks are close to capacity, with the vitrification plant not required to start operating to treat up to 56 million gallons of waste for disposal until 2019.
Double-shell tanks will be needed to store waste for decades until all the waste can be treated.
Some problems in the construction of Tank AY-102, which has an interior leak, were corrected as the next tanks were built.
Workers used three-eighths-inch steel plates for the base of the outer shell of the second tank rather than the one-quarter-inch steel used on the first. The percentage of rejected welds dropped from 36 percent to 10 percent on the second tank, AY-101, which does not have a leak.
Tank AY-102 is slowly leaking waste from its inner shell into the 30-inch-wide space between the inner and outer shells. It's estimated to have leaked 190 to 520 gallons of waste, but a significant portion of the liquid has evaporated, leaving an estimated 20 to 50 gallons of drying waste between the shells.
However, the material detected within the shells continues to be damp, indicating that the inner shell continues to leak, Britton said.
"We're confident that tank waste is not getting outside the secondary containment," Del Scott, project manager for Washington River Protection Solutions, said in a statement.
A team has been formed with members from DOE, Washington River Protection Solutions and the Washington State Departments of Ecology and Health to consider what to do about Tank AY-102.
An existing pump for liquid waste in the tank has been reconnected to the electrical system and methods that also could be used to remove solid waste in the tank are being considered. In addition, another pump has been staged to pump liquid waste from between the shells of the tank, if needed.
Washington Gov. Jay Inslee and Oregon Gov. John Kitzhaber have called for DOE to build more double-shell tanks, both to provide more sound waste storage space and also to help feed waste to the vitrification plant once it starts operating.