LOS ALAMOS, N.M., Aug. 3, 2000 -- A continual issue in the handling of nuclear waste is long-term storage, because internal radiation can cause radioactive host materials to swell or crack, making the stored waste unstable and susceptible to leaching.
Now, a team led by Kurt Sickafus of the Department of Energy's Los Alamos National Laboratory has demonstrated that certain ceramic materials with structures similar to fluorite crystals hold up well to radiation damage because the materials' atoms shift around to accommodate defects caused by radiation damage.
Sickafus, of Los Alamos' Structure and Property Relations Group, and colleagues from Imperial College in London and Osaka University in Japan, detail their research in the Aug. 4 issue of Science.
National laboratories such as Los Alamos, nuclear reactor operators and other creators of nuclear waste could benefit from the new findings, said Sickafus. High-level nuclear waste, such as spent fuel from nuclear reactors, is currently stored in containers designed to last 100 years, he said. But storing nuclear waste requires containment materials that can resist leaching and radiation damage for thousands of years.
"Fluorite-type ceramic materials show promise as safe, radiation-proof materials and should be further developed for containing nuclear wastes," Sickafus wrote in the Science study.
For years researchers have been looking for better storage materials for storing high-level radioactive waste. Recent research has centered on a class of materials that are part of a larger group of ceramics called complex oxides.
To test their theory, researchers tested pyrochlore and fluorite structures. Pyrochlore is a brownish-black mineral oxide found in granitic rocks and pegmatites, coarse-grained igneous rocks. Fluorite is a bluish-green mineral used in the smelting of iron and in the ceramic and chemical industry.
The researchers tested several combinations and discovered that radiation resistance increases when relatively large metallic ions such as zirconium are included in the compound's atomic structure.
"Preliminary radiation damage experiments substantiate the prediction that fluorites are inherently more radiation resistant than pyrochlores. These results may permit the chemical durability and radiation tolerance of potential hosts for actinides and radioactive wastes to be tailored," the researchers wrote.
Other members of the research team include James Valdez, Fuxin Li, Kenneth McClellan and Thomas Hartmann, all of Los Alamos; Manabu Ishimaru of Osaka University; and Licia Minervini and Robin Grimes of Imperial College. Grimes recently came to Los Alamos as a Bernd Matthias Scholar in the Laboratory's Materials Science and Technology Division.
Funding for the work was provided by DOE's Office of Basic Energy Sciences.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.
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