US Department of Energy (DOE) contractor Washington River Protection Solutions (WRPS) announced on 3 July that it had awarded a subcontract to AVANTech for its tank-side caesium removal demonstration project at the Hanford site, which is undergoing a major legacy cleanup programme. This is the third proposal to prepare radioactive waste from the Hanford tank farms for treatment before it is channelled to the plant. The aim is to separate caesium and solid materials from Hanford's underground tanks to provide a low-activity waste stream to the plant when it begins vitrification.  

The tank-side project will use technology previously deployed at DOE's Oak Ridge Site and the Fukushima Daiichi site in Japan. DOE expects the tank-side pretreatment system to deliver low-activity waste by December 2023 or sooner. It is expected to pre-treat 5m gallons of waste. A $17bn vitrification plant is being constructed to treat 56m gallons of radioactive and hazardous chemical waste associated with plutonium production for weapons development after World War II and during the Cold War.

Leaks continue

Meanwhile, reports continue of leakage from waste storage tanks. A new evaluation by WRPS has found that more of Hanford’s newest waste storage tanks could be at risk of developing leaks. DOE is currently emptying the radioactive and hazardous chemical waste from 149 leak-prone single-shell tanks into 28 newer double-shell tanks for storage until the waste can be treated for disposal. WRPS compared the chemistry of the waste in the oldest double-shell tank, which was discovered to be leaking, to the waste in the other double-shell tanks. 
This, and other studies of the double-shell tanks suggest a need to build more waste storage tanks for the 56m gallons of stored waste, according to the Washington Department of Ecology (WDE).  Steve Lowe, WDE’s double-shell tank lead engineer said action is needed sooner rather than later. “Cleanup depends on it.” He added that three of the double-shell tanks that still hold waste had “very high-risk factors” for corrosion, based on information in the new study. Jeremy Johnson, deputy DOE project director for the Hanford tank farms, told a recent Hanford Advisory Board committee meeting that this does not mean the three tanks are leaking or will leak.
The first double-shell tank — Tank AY-102, which dates to 1971 — has been taken out of service and emptied after developing a slow leak from its inner shell into the space between its shells. Initially, the leak was attributed to construction problems, including welds that had to be reworked as many as four times, but subsequent tests indicate that corrosion is the problem. An inspection in 2017 found widespread pitting on the bottom of the inner shell, allowing waste to seep through. The most recent study found three other double-shell tanks — AY-101, AZ-101 and AZ-102 — hold waste with similar chemistry to that which caused corrosion in Tank AY-102.
Two of the tanks with possible waste chemistry issues have spots with thinning in a ring around the wall of the inner shell. Ultrasonic testing has also found thinning of the steel of the outer shell of nine of 11 of the double-shell tanks checked. 
DOE has relied on an independent Tank Integrity Expert Panel, which met in late June, to provide recommendations on the Hanford tanks. The panel has “found areas of interest in time to take action before they become a problem,” Johnson said. However, WDE said double-shell tank space is limited, with several of the tanks at risk. 

Double-shell tanks have a capacity of at least 1m gallons. DOE noted that when the vitrification plant begins operation, some 12m gallons of capacity will be freed up during the following decade in the double-shell tanks making it possible to empty more single-shell tanks. Nonetheless, by then the oldest of the double-shell tanks will already be 50 years old. WDE pointed out that some of the tanks will remain in service longer as the plant will operate for another 40 years.

DOE said a chemistry-control programme for the double-shell tanks would be revised and core samples will be collected to analyse the waste at the bottom of the three most at-risk tanks. To prevent pitting in a ring around tanks from ventilation system condensate, the liquid now will be treated elsewhere at the nuclear reservation, rather than going into the tanks. Robots small enough to be used in the ventilation spaces between the bottoms of the two shells are being developed and could learn more about the condition of the tanks.