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CAS Connect May 2016

Key to nuclear disposal in ancient glass?

Glass manufactured 1,500 years ago could hold the key to challenges in nuclear waste disposal today.

An interdisciplinary team of WSU researchers, led by chemistry doctoral student Jamie Weaver, is studying ancient glass and rock defense walls found at the mysterious Broborg hill-fort in Sweden to determine if similar materials could be used for long-term storage of radioactive and chemical waste at Hanford and other nuclear cleanup sites.

Jamie Weaver
Jamie Weaver

Weaver and colleagues in the WSU School of Mechanical and Materials Engineering are analyzing how the passage of a millennium and a half has altered and corroded the glass. They report on their work in the May issue of American Ceramic Society Bulletin.

“Glass is a really well-established immobilizer of nuclear waste, but we are still working on modeling its durability over thousands of years,” Weaver said. “The Broborg hill-fort samples are helping us to understand the long-term durability of glasses that could be made from Hanford’s radioactive waste, currently being held in underground storage tanks.”

Technique ‘like nowhere else in the world’

A sample of a fused Broborg hill-fort glass overlaid with cross-sectional X-ray tomography data. This non-destructive technique lets scientists image key internal portions of the sample.
A sample of a fused Broborg hill-fort glass overlaid with cross-sectional X-ray tomography data. This non-destructive method lets scientists image key internal portions of the sample. Photo courtesy of PNNL

At Broborg, a tribe of people around 1,500 years ago melted rocks to strengthen fortifications against invaders. They piled boulders left by ancient glaciers into two large rings, put black amphibolite rocks on top, layered the wall with charcoal and burned it. As the rock melted, it infiltrated the boulders and cooled as glass, acting as glue for the wall.

“The technique is like nowhere else in the world,’’ said John McCloy, associate professor in the WSU School of Mechanical and Materials Engineering and co-author on the paper. “They heated the rock until it melted—and it is still quite intact 1,500 years later.’’

The Broborg site is valuable because researchers know how old the glass is and how it has worn. This knowledge is helping the researchers improve their models for long-term environmental protection, McCloy said. “We need relevant timescales.’’

The project is funded by the U.S. Department of Energy (DOE) Office of River Protection, which is developing a testing protocol for nuclear glass to meet U.S Environmental Protection Agency disposal regulations. The work is supported through the DOE Office of Environmental Management and is a collaboration between the National Historical Museums and Luleå University in Sweden, the Pacific Northwest National Laboratory (PNNL) in Richland, Wash., WSU, and the Smithsonian Institution’s Museum Conservation Institute.

Inspired by pre-technology expertise

Weaver, an intern at PNNL, said she has gained appreciation of the ancient people and their techniques as she has studied them.

“Without electricity and all the technology that we have today, they did some really cool work,’’ she said. “It’s pretty awesome how smart and creative they were.’’

In addition to her research with McCloy, Weaver is working with her other doctoral advisor, Nathalie Wall, associate professor of chemistry, to develop new ways to increase the amount of radioactive material that can be stored in glass canisters.

“There is a huge crossover in material science and chemistry when you get to studying glass, and I have really appreciated the opportunity to work with experts in different disciplines,” Weaver said. “It has forced me to expand my skillset and outlook.”

Both of Weaver’s projects fit with WSU’s Grand Challenges initiative to stimulate research to address some of society’s most complex issues. It is particularly relevant to the challenge of “National Security” and its theme of advancing safeguards through basic research.

Washington State University