DOE says radioactive waste tank not leaking

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 was triggered 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 inside 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.

Historical documents and the operational history of the tank are being studied.

DOE contractor Washington River Protection Solutions also continues to use a videocamera to inspect the space between the shells of Tank AZ-101.

It is being lowered down each of the multiple risers that extend from the ground into the space between the shells of the underground tanks to check for any anomalies.

Contamination may have made its way into the space between the shells in past decades as waste was transferred in and out of the tank. It also is possible that precipitation may have leaked into the space, carrying contamination with it.

Last spring another tank, AY-101, was suspected of leaking based on elevated radiation readings. DOE later concluded that the reading was linked to historical contamination of the space between its shells, possibly as long ago as 1976.

DOE’s double-shell tanks have been watched more closely since a leak was confirmed in 2012 from the inner shell in the oldest of the Hanford nuclear reservation’s double-shell tanks, AY-102. No waste is believed to have breached the outer shell to contaminate the soil beneath the tank.

The tank was emptied of radioactive waste, with waste retrieval completed late this winter 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.

Workers immediately left the area and follow-up surveys at a trailer used for changing out of protective clothing found not further contamination. Workers were wearing supplied air respirators to protect against breathing chemical vapors associated with tank waste.

All workers were cleared for normal duty.

This story was originally published May 24, 2017 at 2:47 PM with the headline "DOE says radioactive waste tank not leaking."