Vitrification of radioactive waste into glassy solids is the most popular approach for disposal. By spraying radioactive sludge into a high-temperature combustor, essentially all the water and other nonradioactive material could be removed, leaving only the radioactive metallic elements to be vitrified for burial. Under optimized conditions, up to 99.99 percent of the metal ions in a waste stream can be scavenged in the combustor.
"That kind of efficiency would be great for most applications, but it's not good enough when dealing with radioactive waste," said Alexander Scheeline, a professor of chemistry at Illinois. "Understanding the cause of the unscavenged fraction and devising a way to reduce it are essential if thermal processing is to be used for nuclear waste treatment."
One possible explanation is that large "rogue" drops are responsible for the unscavenged metals, Scheeline said. These drops do not pass through the hottest zones in the combustor, resulting in only partial vaporization.
To investigate the role of rogue drops in this process, Scheeline and his colleagues -- Illinois postdoctoral researcher Jerry Cabalo, Arizona professor and head of chemical and environmental engineering Jost Wendt, and Arizona graduate student John Schmidt -- developed an optical system to monitor drop sizes and trajectories at very high spatial resolutions.
"In the thermal waste destruction process, small particle formation is also very important," Scheeline said. "Metals released into the gas phase readily
Contact: James E. Kloeppel
University of Illinois at Urbana-Champaign