Areva and the University of Idaho have signed an agreement to develop technology for recovering uranium from incinerator ash at Areva's uranium fuel plant in Richland, Washington state. The process also reduces the amount of ash classified as radioactive waste.
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. Wai and Koegler have worked together for four years on the uranium extraction project.
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. During normal operation, common items including filters, rags, gloves and paper wipes become contaminated with uranium. This low-level waste (LLW) has been routinely incinerated to reduce its volume, and chemical analysis has shown the Richland stockpile to contain more than two tonnes of usable enriched uranium.
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 LLW. Denise Woernle of Areva could not put a figure on the reduction in LLW the process could give, but confirmed it as an added benefit.
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.
The technology licensing agreement will allow Areva to use several of Wai's discoveries to extract the metals from the ash. Areva has provided funding for the research and will gain rights to the University of Idaho's share of a joint patent developed in cooperation with Wai that further separates the enriched uranium from the extracted metals.
"Radioactive waste is a big problem facing the United States and the entire world," Wai said. "We need new, innovative technology, and I think supercritical fluid is one such technology that will play an important role in the very near future."