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Preliminary tests show the oldest of the double-shelled underground tanks used to hold hundreds of thousands of gallons of radioactive waste at Hanford may have leaked material from its inner wall.

Material was discovered in August in the space between the double walls known as the annulus. At that time, Department of Energy officials said it could be material left over from construction or from some other source like a pipe.

On Thursday, the DOE announced the material in the annulus is largely consistent with what's inside the tank. That tank, AY-102, holds highly radioactive waste that was transferred from Hanford's aging single walled tanks.

Officials stressed there is no sign of leakage from the outer shell of AY-102, which is covered with steel reinforced concrete, and the entire tank is buried underground.

But watchdog groups have expressed concerns if one double shell tank is beginning to degrade others may too, which could lead to leaks that could contaminate groundwater.

The DOE said it will make a final decision on the status of tank AY-102, which could be made as early as the end of next week.

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