Chien Wai, a chemistry professor at the University of Idaho, has developed a process that uses supercritical fluids to dissolve toxic metals. When this process is coupled with a purifying process developed in partnership with Sydney Koegler, an engineer with Areva and former student at the University of Idaho, enriched uranium can be recovered from the ashes of contaminated materials.
A supercritical fluid - in this case carbon dioxide (CO2) - is any substance raised to a temperature and pressure at which it exhibits properties of both a gas and a liquid. When supercritical, the substance can move directly into a solid like a gas, yet dissolve compounds like a liquid. CO2 reaches its supercritical state at a pressure of about 6.9 MPa and a temperature of 31°C. When the fluid's pressure is returned to normal, it becomes a gas and evaporates, leaving behind only the extracted compounds. Wai commented that supercritical CO2 has been used for decades to remove caffeine from whole coffee beans.
Areva plans to apply the process to recover uranium from 32 tonnes of ash at its Richland nuclear fuel plant. In addition to the recovery of two tonnes of uranium, the radiotoxicity of the post-process ash is reduced, thereby allowing some to be reclassified as other than low-level waste (LLW).
Construction of the ash-uranium recovery plant will begin in 2008 and should be operational in 2009. It will take about one year to process the 32 tonnes of ash at Richland, after which the plant could process ash from other LLW generators in the nuclear energy and nuclear medicine industries.
LLW from a nuclear plant
In other nuclear news, Canada is extending the operating life of the Gentilly 2 nuclear reactor until 2040
Other methods of handling low level waste
A large nuclear power plant that generates electricity for a half million people produces approximately 25 tons of spent fuel annually. An equivalent coal plant produces 10 million tons annually of air pollutants, potentially hazardous ash, and other wastes.
Nuclear waste discussed at Berkeley