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Image: Double-shell tank
This graphic shows a cutaway view of a double-shell nuclear waste storage tank at the Hanford Site. (Credit: Washington State Department of Ecology)

Workers at Eastern Washington’s Hanford Site are trying to track down the source of radioactive contamination at an underground waste storage tank, one week after an internal leak sparked concern about a different tank at the facility.

Both double-walled tanks were put into service 45 years ago to hold radioactive and chemical wastes from plutonium production for the U.S. nuclear weapons program. Each tank is 75 feet wide and can hold a million gallons of waste.

One of the tanks, AY-102, has been the subject of concern for years. That’s where an alarm went off on April 17, when liquid waste and sludge leaked through the tank’s inner wall and built up to a depth of 8 inches in the space between the inner and outer walls.

That leak was cleaned up, and nearly all of the waste that was in AY-102 has been transferred to other storage tanks. But now the U.S. Department of Energy says air filter samples from the space between the walls in the other tank, AY-101, registered higher than normal levels of radioactive contamination this month.

“While these readings were higher than normal, they were well below the alarm level,” the Energy Department’s Office of River Protection said in a statement.

So far, visual inspections and detection instruments have shown no evidence of a leak in the tank’s inner wall, but workers at the Energy Department and its contractor for the tank farms, Washington River Protection Solutions, are continuing to look. “DOE is conducting engineering analysis and assessments to determine potential causes of the readings,” the department said.

Alex Smith, the Washington State Department of Ecology’s nuclear waste program manager, told GeekWire that the anomalous levels do not appear to pose a risk to the public. Nevertheless, she said state officials have a “keen interest” in getting the situation at Hanford resolved.

“We are very concerned that there is an anomaly, and that these [tanks] aren’t a good long-term alternative for storing this waste,” she said. A ruling issued by a federal judge last month lays out a long-term plan for Hanford’s cleanup and leaves the door open for requiring new storage tanks if the plan isn’t met.

A Seattle-based environmental group called Hanford Challenge issued a statement today saying that the elevated levels suggest AY-101 is failing.

“The presence of these radioactive materials in the outer shell of the tank, known as the annulus, is a solid indicator that the primary shell of the tank has failed and is leaking high-level nuclear waste into the outer shell,” Mike Geffre, a former Hanford worker, was quoted as saying. “This is the same indicator that tipped off workers that AY-102 had failed.”

Hanford Challenge said AY-101’s problems could have serious implications for the site’s storage facilities.

“Simply put, Hanford is nearly out of double-shell tank space, especially after pumping out AY-102 and emptying some of the shakier single-shell tanks,” said Tom Carpenter, executive director for Hanford Challenge. “There is no other realistic option but to begin building new tanks immediately.”

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