DOE: Investigation of contamination finds no tank leak via Tri-City Herald

The Department of Energy does not believe there is a leak in another one of Hanford’s double shell tanks holding radioactive waste, it announced Wednesday.

The initial phase of an investigation ruled out the possibility that contamination found on a robotic crawler last week was from a leak within Tank AZ-101, according to DOE.

An analysis was done of the contamination on both the robotic crawler and on the filter of an air monitor that alarmed the night of May 18, finding the same mix of radioactive isotopes.

But the radioactive isotopes did not match those in the current mix of the 800,000 gallons of waste being held in Tank AZ-101, according to DOE.

It appears that the crawler may have gotten into some older contamination in the space between the shells of the tank and kicked it up to contaminate the air filter, according to DOE.

The investigation is continuing to find the source of the contamination, which also spread to the leg of the protective clothing worn by a Hanford tank farm worker.

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The tank was emptied of radioactive waste, with waste retrieval completed this spring at a cost of more than $100 million. The waste was transferred to other double shell tanks.

Hanford’s 149 leak-prone single shell tanks are being emptied into the newer double shell tanks until the waste can be treated for disposal. Much of the waste is expected to be immobilized in glass logs at the Hanford vitrification plant.

With the oldest of the double shell tanks out of service, the remaining double-shell tank space is limited. 

In the incident last week, workers were pulling a robotic crawler out of a riser after it had been used to check a section of the space between the inner and outer shells of the tank. The inspection was part of a scheduled ultrasonic study of the tank’s condition.

After the contamination was discover on the crawler, a radiological survey detected low levels of contamination on the protective overalls of the worker who operated the crank to lift the crawler out. No contamination spread to the worker’s skin.