In a finding that could just as likely lead to a new, cheap method of chemical waste cleanup as it could predict disaster at the nation's worst nuclear waste site, researchers at Northwestern University and the University of Notre Dame have shown that common soil minerals can work with ionizing radiation to break down toxic wastes into simpler compounds. The finding, however, also serves as a warning that breakdown products in enclosed storage tanks may build up pressure and explode.
In laboratory experiments, the researchers showed that alumina, an oxide of aluminum that is found in many soils, can greatly accelerate chemical reactions in which gamma rays break down toxic chlorinated chemicals. Silica and other oxides -- clay -- in soil may behave similarly. Gamma rays are high energy X-rays given off by many of the highly radioactive wastes produced in weapons manufacture, such as cobalt-60.
The good news is that gamma irradiation thus may be an effective means of degrading some highly toxic pollutants, such as dioxin or PCBs, in contaminated soil. The bad news is that 177 huge underground tanks on the Hanford Nuclear Reservation in eastern Washington, which hold 54 million gallons of high-level radioactive and chemical waste, may face an increasing risk of rupture or explosion as volatile gases, including hydrogen and perhaps methane, are generated as the chemicals are broken down by minerals in the tanks.
"They're big cauldrons of radioactive soup," says Kimberly A. Gray, associate professor of civil engineering at Northwestern's Robert R. McCormick School of Engineering and Applied Science. Gray conducted the new study with physical chemist Prashant V. Kamat of Notre Dame's Radiation Laboratory and Northwestern graduate student George A. Zacheis. The results are reported in the April 8 issue of the Journal of Physical Chemistry.
The Hanford tanks, Gray said, contain radioactive metals and nonradioactive
metal oxides and organic chemicals tha
Contact: Bill Burton