Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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14 SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM Tank Integrity Studied at Radioactive U.S. Waste Storage Site B uilt in 1943, the decommis- sioned Hanford nuclear production complex on the Columbia River in eastern Washington was once home to the world 's f irst full-scale plutonium reactor. 1 The site's last reactor closed in 1987, and in 1989, the U.S. Department of Energ y (DOE) (Washington, DC, USA) began large-scale cleanup efforts. As part of those efforts, the DOE transferred radioactive and hazardous chemical waste from 149 single-shell tanks—built between 1942 and 1964— into 28 newer double-shell tanks for enhanced storage security until the waste can eventually be treated for dis- posal. However, the f irst double-shell tank to be built—Tank AY-102, con- structed in 1971—was taken out of ser- v ice in 2012 after a slow leak was discov- ered from its inner shell into the annular space between the inner shell and the secondar y steel containment liner. The waste was contained in the annulus, and there is no indication that it leaked into the env ironment. 2 According to the DOE, the retrieval of the AY-102 tank cost more than $100 mil- lion and lasted more than a year. An inspection in 2017, after most of the waste had been removed from the tank, found widespread pitting at the base of the inner shell. Should other tanks at Hanford be taken out of service, costs could rise exponentially. In 2018, a new investigative report delivered by the DOE's Off ice of River Protection (Richland, Washington, USA) f inds that other tanks at the facility also may have held waste with chemistry simi- lar to waste stored in AY-102. However, the DOE cautions that it is too soon to tell whether similar leaking has or will occur. Testing is ongoing at Hanford, which holds a total of ~56 million gal (211,983 m 3 ) of radioactive waste. "The results of this study should not be interpreted as indicating that any of the storage tanks are currently leaking, or will leak, from the primary liner to the secondary liner, or from the tank to the environment," says Jeremy Johnson, deputy federal project director with the DOE's Off ice of River Protection. Johnson delivered his comments at a June 2018 meeting of the Hanford Advisory Board 's tank waste committee. 3 In the latest round of testing, investigators found that two tanks had spots showing significant thinning in a ring around the shell's wall. The site's standard tank integrity pro- gram has included a video inspection of the tank wall and annulus f loor areas approximately every three years, and an ultrasonic inspection every ~10 years, along with laboratory testing of the waste chemistry. Over the longer term, the liquid waste stored at Hanford will be vitrified. Vitrification is accomplished by mixing waste from the tanks with glass-forming materials in high-temperature smelters, which the DOE says makes the material easier to store safely. However, the planned vitrification plant at Hanford is not sched- uled to begin operations until at least 2021. Furthermore, the process of remov- ing all the liquid waste from the tanks and securely transporting it to the vitrification plant is expected to take many years. Thus, in the interim, maintaining the seals on the current tanks is essential. An aerial shot of the decommissioned Hanford nuclear site. Photo courtesy of DOE. MATERIAL MATTERS

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