Contamination found, Hanford tank being checked for interior leak
A planned inspection Thursday night of a Hanford double-shell tank holding radioactive waste found contamination that might indicate a leak between the shells of the tank.
One of Hanford’s 28 double-shell tanks already has been taken out of service because of an interior leak.
Gov. Jay Inslee called reports of a possible leak within a second tank on Friday “alarming.”
“We are not aware of any nuclear waste leaking outside the AZ-101 double-shelled tank, but we expect the U.S. Department of Energy to immediately investigate and report on the source of the contamination,” he said.
Workers used a robotic crawler Thursday to inspect the space between the two shells of tank AZ-101. They found the contamination when the crawler was pulled out of the tank that night.
Radioactive contamination also was found on the leg of the protective clothing of one worker. He had turned the crank to lift the 40-pound crawler out of the space between the tank’s shells.
The contaminated section of the clothing was cut off, which is the standard process to prevent cross-contamination, according to Washington River Protection Solutions, the DOE Hanford tank farm contractor. Follow-up radioactive surveys showed no contamination remained on the worker’s clothing.
The crew stopped work immediately, as is policy, and left the area, according to DOE.
More checks at a change trailer showed no other workers were affected and all were cleared for normal duty. They were wearing supplied air respirators to protect against chemical vapors associated with tank waste.
An air monitor within the space between the shells of the tank alarmed during the incident. However, leak detection instruments already installed in the space between the shells did not detect any liquid on the floor of the space between the shells, according to DOE.
Plans are being made to use video equipment to inspect the space between the shells to learn more. The inspection is expected to be done next week.
“We are taking a conservative approach to investigate the source of the contamination,” said Peter Bengtson, spokesman for Washington River Protection Solutions.
Over the weekend, the crawler will be taken to Hanford’s 222-S Laboratory to have its contamination analyzed and possibly identified.
“This will help us better understand the potential source,” tank farm workers were told in a memo late Friday afternoon.
The filter from the air monitor that alarmed also has been removed and is being studied for more information about the incident.
Work started Thursday using the crawler as part of an ultrasonic inspection of the integrity of the tank, which is done every eight to 10 years. This is the first time the tank integrity inspection has included a careful look at the floor of the space between the shells. Video inspsections are done of the space between the shells every three years.
The crawler was lowered down one of the risers that allow access from the ground into the space between the shells of the underground tank.
It had finished inspecting the area between two of the risers, or roughly 10 percent of the bottom of the ring between the shells, when it was pulled out to be inserted down the next riser.
The contamination found on the crawler was at more than three times the anticipated amount. Some double-shell tanks have some contamination between the shells from previous work moving waste into and out of tanks, or precipitation leaking into the space between the shells.
Historical data is being pulled by contractor employees to learn more about what contamination may have occurred previously.
In the last year, the oldest of 28 double-shell tanks at Hanford, AY-102, was emptied after a leak was discovered from its primary shell into the space between its shells. There is no evidence that waste leaked into the soil beneath the underground tank.
“Today’s news of another potential leak in a tank at Hanford only strengthens my resolve to hold the Department of Energy accountable for its responsibility to clean up this contaminated site,” said state Attorney General Bob Ferguson. “This isn’t the first potential leak, and it won’t be the last.”
The news of an investigation into a possible second double-shell tank leak “is just another illustration of how tenuous the situation is,” he said.
The state required DOE to empty Tank AY-102 because it no longer complied with state regulations.
The AY and AZ areas hold two tanks each. They were the first four double-shell tanks built, all by the same contractor. Thicker steel was used for the AZ Farm tanks, however.
Unlike the double-shell tank currently under investigation, liquid was found on the floor of the space between the shells of tank AY-102.
The AZ tanks were built between 1970 and 1974, with a planned service life of two decades. Both of the AZ tanks have held waste since 1976, or more than double the time planned.
Waste from Hanford’s 149 older, leak-prone single-shell tanks is being emptied into newer double-shell tanks, but space is limited, particularly with tank AY-102 already taken out of service.
Tank AZ-101 holds 800,000 gallons of radioactive and hazardous chemical waste left from chemically processing irradiated uranium fuel to remove plutonium for the nation’s nuclear weapons program.
Hanford has 56 million gallons of similar waste held in both its single- and double-shell tanks until it can be treated for disposal. Much of the waste is planned to be treated at the vitrification plant under construction.
The state of Washington had asked a federal judge to require more double-shell tanks to be built at Hanford as new court-enforced deadlines for Hanford environmental cleanup were set.
Judge Rosanna Malouf Peterson declined to require more tanks in a 2016 ruling on the consent decree, but said that the state may repeat its request if DOE misses deadlines for emptying single-shell tanks because of a lack of space in double-shell tanks to hold the waste.
DOE told the court that building new double-shell tanks would be extremely expensive, estimating the cost of each at $85 million to $150 million. It did not want to divert money from other projects at Hanford or other DOE nuclear cleanup sites.
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