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More Corrosion Possible in Hanford Tanks

Tuesday, July 3, 2018

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Recently disclosed findings indicate that the kind of pitting corrosion that led to the decision to decommission the oldest double-shell radioactive waste storage tank at Washington’s Hanford Nuclear Site could pose a risk for other tanks at the site, and moisture could be causing destructive corrosion of the secondary containment layer of the tanks.

A report delivered by the U.S. Department of Energy’s Office of River Protection at a meeting of the site’s advisory board Tank Waste Committee late last month noted that other tanks, including AY-101, AZ-101 and AZ-102 “may have held waste with chemistry similar to AY-102,” the nearly 50-year-old dual-shell tank where severe corrosion was found last year. Two of the tanks receive condensate from ventilation systems, which the report notes could accelerate corrosion.

Hanford Site
Tobin Fricke, CC BY-SA 3.0, via Wikimedia Commons

Constructed in 1943 and 1944, the Hanford site, on the Columbia River in eastern Washington, was the world’s first plutonium production site.

While the corrosion found in AY-102 caused leaks from its primary liner into its secondary containment, the outer steel liners of the DSTs are also at risk. Recent ultrasonic testing of the outer shells of 11 DSTs at the site showed nine instances of reduced wall thickness, according to the DOE. The agency says moisture may penetrate the concrete shells around the tanks, coming in contact with the steel outer liners.

According to the advisory board, an investigation is ongoing to determine whether the outer shell of tank AP-102 has already failed.

Radioactive Waste

The tanks at Hanford’s tank farm hold dangerous waste including uranium 235, plutonium 238 and strontium 90. There are 28 DSTs at the site including the decommissioned AY-102, which held 850,000 gallons of waste. The secondary containment is meant to serve as insurance against a leak of radioactive waste into the ground should a failure of the primary steel shell occur; the DSTs were built between 1968 and 1986.

Another 139 single-shell tanks, built between 1942 and 1964, exist at the massive site.

The Washington state Department of Ecology says at least 67 of the SSTs have leaked more than 1 million gallons of waste into the ground total. The state agency has tried to force the DOE, which oversees the site, to build more DSTs to contain the waste more safely, but in 2016, a judge sided with the federal entity and declined to force the DOE to build more DSTs. The site’s advisory board says it has also repeatedly advised the DOE to increase its DST capacity.

Harford corrosion
Department of Energy

Corrosion was found last year in the inner shell of tank AY-102, the oldest dual-shell tank at the site at nearly 50 years old.

In the short term, the DOE says in the report, it plans to look at the application of corrosion inhibitors and will take steps to stop moisture from reaching the outer shells of the DSTs. The agency says it is evaluating methods of repairing areas of the tanks affected by corrosion damage.

If more DSTs are found to be failing, it could have an impact on the timeline of the transfer of waste from the site’s SSTs to its DSTs, and it would come with a massive cost. According to the advisory board, the retrieval of AY-102 cost more than $100 million and took more than a year.

A report is due by September on the structural integrity of the SSTs at the site; the last major assessment, in 2002, found that the tanks would be sound through at least this year, but did not guarantee against leaks.

The liquid waste being stored in the tanks at Hanford is waiting to be vitrified, or converted to a more stable, glasslike solid form that will be easier to store safely. The vitrification plant at the site is expected to begin operations no sooner than 2021, at which point the liquid storage tanks will begin to be emptied. Even if the facility opens on time, it will take well over a decade before the liquid waste is removed from the tanks.

Site History

Constructed in 1943 and 1944, the Hanford site, on the Columbia River in eastern Washington, was the world’s first plutonium production site. It was where the first nuclear bomb ever tested was built. The last reactor on the site closed in 1987, according to the DOE, and in 1989, the government began a large-scale cleanup effort.

Hanford tank farm

The site includes 28 dual-shell tanks and 139 single-shell tanks housing millions of gallons of radioactive waste.

The site has been subject to controversy for years, related to ballooning costs, alleged impropriety on the part of contractors and safety concerns for workers.

Last year, a tunnel housing railcars containing radioactive waste collapsed, leading to a shelter-in-place order for nearby workers; no contamination was released, according to the DOE. Earlier this year, the Government Accountability Office released an audit of the construction of the new waste treatment plant, blaming the DOE and design-build contractor Bechtel National Inc. for ongoing quality-assurance problems.


Tagged categories: Carbon Steel; Corrosion; NA; North America; Quality Control; U.S. Department of Energy

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