Contacts: Dr. Chien Wai, 208-885-6552, Bill Loftus, 208-885-7694
Aug. 21, 1998 A photograph of Brenda Waller in her laboratory is available electronically through [email protected]
IDAHO WORK SUGGESTS BETTER NUCLEAR, HAZARDOUS WASTE CLEANUP PROCESS MOSCOW, Idaho -- A process already used to extract caffeine from coffee beans and bittering agents from hops shows promise for a new environmentally friendly way to handle nuclear waste, say University of Idaho chemists. Brenda E. Waller, a UI graduate student from Durand, Ill., presented her group's research findings during the American Chemical Society's annual conference at Boston Aug. 23. Waller's research continues that of her co-authors on the paper, UI Chemistry Department Chairman Chien M. Wai and researcher Mike J. Carrott of British Nuclear Fuels Ltd., which helped pay for the work. "This may be a cleaner way to reprocess spent fuels and hazardous waste," Wai said. "This is one example of green chemistry." The Idaho researchers studied the use of supercritical fluid carbon dioxide to extract a form of uranium commonly found in spent fuel from nuclear power plants and in nuclear waste. Supercritical fluids such as carbon dioxide, water or ammonia exist only at specific temperatures and high pressures. They are dense like liquids yet also have gas-like qualities, such as expanding to fill their containers. The work with supercritical carbon dioxide promises a better way to remove uranium and plutonium from a variety of materials so they can be handled more safely. The work's promise was the focus of an article in this month's "Chemistry in Britain," a journal with worldwide circulation, by Wai, Neil Smart at BNFL in Sellafield, England, and Cindy L. Phelps. She received her doctorate from Idaho last year and is teaching at nearby Lewis-Clark State College at Lewiston, Idaho. The Idaho research has also been noted in other publications including the "Journal of Chemical Education" and "Chemical and Engineering News." The traditional PUREX, shorthand for plutonium and uranium extraction, process is used worldwide. In it, the nuclear materials are subjected to an acid process, then extensive washing with hydrocarbon solvents, typically kerosene, to remove the plutonium and uranium. The Idaho research showed the best results extracting uranium that had already been bathed in nitric acid, the first step in the traditional process in use since World War II. Using supercritical carbon dioxide promises to replace the second half of the PUREX two-step, the washes with organic solvents. That old extraction process created millions of gallons of hazardous and nuclear waste now in storage at the Hanford nuclear reservation in central Washington and elsewhere. The UI work may help efforts to clean up nuclear and hazardous wastes at the Idaho National Engineering and Environmental Laboratory near Idaho Falls as well. The supercritical carbon dioxide also works directly, although so far less efficiently, on uranium compounds found in spent fuel or nuclear waste before the acid is used, potentially eliminating the wastes produced by that step. Waller and her colleagues found supercritical carbon dioxide dissolved uranium compounds formed during the traditional process more easily than any other metal tested so far. She found the best results at relatively low temperature, 40 degrees Centigrade, and moderate pressure, 225 atmospheres or approximately 3,300 pounds per square inch. Under those conditions, the solubility of uranyl nitrate, the uranium compound under study, in supercritical carbon dioxide rivals that in organic solvents, a rarity in the world of supercritical fluids. The promise of supercritical carbon dioxide is it can extract the radioactive or other hazardous materials without creating additional hazardous materials. Once the supercritical fluid extracts the targeted compound the pressure can be reduced, allowing the carbon dioxide gas, the same gas people exhale, to boil off and leaving the compound behind. The carbon dioxide can be captured and recycled. In coffee decaffeination, the caffeine extracted from the beans is sold to soft drink manufacturers. Waller and Wai believe further work with that process offers the greatest hope of dealing with the world's nuclear and hazardous waste stockpiles. Reprocessing of spent fuel rods from nuclear power stations is prohibited in the United States but is practiced in Britain and France. The university's work is focused on the basic chemistry involved in the process, Wai said. Adapting it to large-scale production would require the efforts of chemical engineers and other scientific disciplines. Waller's work has been done with tiny amounts of laboratory-grade uranium compounds, not the complicated mixtures found in wastes or spent fuel rods. The real world would present far more complicated issues, she said. Supercritical fluids show promise in dealing with such complicated mixtures, too, Wai said. By varying the pressure and temperature, carbon dioxide's ability to dissolve various compounds changes. That property could allow focusing the extraction process on specific elements. Wai's research has explored the realm of supercritical fluids for nearly a decade. It's that experience, that drew British Nuclear Fuel's interest, said Neil Smart at Sellafield, England. "The research area Chien is working on is very leading edge and original," Smart said. "Idaho is leading and Chien is the leading man in the world." The university's work, which Wai notes has been aided with the financial support of the U.S. Department of Energy and British Nuclear Fuels, has yielded three patents already. The UI group has already applied for three or four more patents as a result of the supercritical fluids work. bl-8/20/98
RSS