Regular routine checks and inspections of the waste tanks at Hanford have scientists wondering about a possible 2nd tank that might be leaking. It's tank AY-101, the second-oldest of the double-shell tanks, and dates back to about 1969.

AY-102 is the most well-known tank, and it's being pumped out due to leaking between the two shells. 23 of these double-shell tanks, which can each hold one million gallons of waste, are located at Hanford. They were intended to replace the older single-shell tanks that date back decades.

During a routine inspection, workers found unusually high radiation readings between the shells, or the annulus, of tank AY-101. However, cameras lowered into the area and a series of visual inspections didn't show any leakage.

Officials say it could be previously undetected radiation from radiation and americium that can spread easily. It could also be from radioactive material found in the ventilation system that helps disperse the heat and fumes from the waste.

AY-101 was also inspected in 2012, 2013 and  2014 and showed no leaks. AY-102 is the oldest tank at Hanford, and it's being pumped due to leaks. It apparently also had extensive construction problems when it was being built 47 years ago.

Officials admit there could be a leak in an area not seen by the cameras, but are also considering the ventilation theory or possible other causes. They plan to make another inspection of the annulus, or space between the walls, in the near future.