The International Information Center for Geotechnical Engineers

Vitrification

 Case Study I

  • Hanford Tank Waste Treatment and Immobilization Plant (the Vit Plant)

 

The Hanford Vit Plant is being built in southeastern Washington State by the Bechtel National, Inc. Once completed, it will be the world’s largest radioactive waste treatment plant. It will process and stabilize 56 million gallons of radioactive and chemical waste. The radioactive waste to be treated is a byproduct of national defense plutonium-production efforts during World War II and the Cold War. More than one-third of the waste have already leaked, contaminating the subsurface and the river nearby. As introduced before, soil vitrification is an effective method of treating radioactive waste. In this plant, waste will be blent with glass-forming materials and heated to more than 1100 degrees Celsius. The mixture is then poured into stainless steel canisters to cool and solidify, which makes it stable and impervious. Then the vitrified waste within the canisters can be disposed permanently and safely. The radioactivity will safely dissipate over hundreds to thousands of years.

 

There used to have nine former nuclear reactors and associated processing facilities at the location of the Hanford Site. From 1944 to 1987, these reactors were used to produce materials for atomic weapons associated with America's defense program. The reactors generated billions of gallons of liquid waste and millions of tons solid waste that must be cleaned up.

 

The plant includes four major nuclear facilities, which are pretreatment, low-activity waste vitrification, high-level waste vitrification and the analytical laboratory. The project is challenging because the magnitude of the treatment plant is very large. It requires more than 260000 cubic yards of concrete, 40000 tons of structural steel and nearly 1 million feet of piping.

The waste will be delivered from the underground storage tanks to the Vit Plant through a series of underground transfer lines. The "pipe-in-pipe" system ensures that there are no leaks of materials during the transfer. The waste will then enter the pretreatment facility, where the water is removed first. After that,  solids are filtered out using ultra-filtration technology and an ion exchange process removes the remaining soluble, highly radioactive material. The waste is then separated into low-activity and high-level waste streams for the Low-Activity Waste Vitrification and High-Level Waste Vitrification facilities. A flow chart of this process can be viewed below:

vitrification_case_study.jpg

Recently, Hanford plant has been reported to has a leakage of radioactive waste. At least six tanks are leaking before being vitrified, which brings significant environmental issues to local ecosystem and human health.

 

For more information regarding to the construction process, the safety issues and so on, please visit the website of the Hanford Vit Plant: http://www.hanfordvitplant.com/

 

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