RICHLAND, Wash. - Researchers at the Pacific Northwest National Laboratory (PNNL) and University of Cincinnati recently developed a method to measure a form of the radioactive element technetium-99 in nuclear waste stored in the underground tanks at the Hanford Site.
The site’s tank waste contains hundreds of chemical components. Technetium is present in the waste in multiple chemical forms with different properties and behaviors during waste processing. The researchers are focused on the non-pertechnetate form of technetium, which is challenging to characterize and quantify under various treatment conditions. The pertechnetate ion is a predominant chemical species containing technetium in nuclear waste. The researchers have begun characterizing other species, known as non-pertechnetate.
It’s important to know how much technetium is in the tanks and have a means to monitor the amounts in the different chemical forms during the cleanup process. Waste is processed through vitrification - a process in which the material is mixed with glass-forming agents, heated, and melted - to produce stable glass logs.
The non-pertechnetate compounds are believed to be bound to certain other waste components and are indistinguishable from other constituents in tank waste using the usual analytical techniques.
Key to the method developed at PNNL’s Radiochemical Processing Laboratory is a pretreatment solution that converts the hard-to-detect, non-pertechnetate technetium compounds into compounds that glow under intense light. This procedure makes them easily distinguishable from the other tank waste components and the amounts of non-pertechnetate technetium can be determined from the intensity of the glowing light.
Shirmir Branch developed the method for her doctorate research at the University of Cincinnati in the research group of professor William Heineman, and in collaboration with PNNL in the group of Dr. Sam Bryan. She created the procedure using rhenium, which has similar chemical properties to technetium but is not radioactive. When mixed with a specially developed pretreatment solution, the non-pertechnetate rhenium converts to an intensely luminescent complex that can be detected in the presence of other waste constituents, Branch found.
Branch then used that procedure with the non-pertechnetate technetium, and it worked well in tank waste simulant and a real tank waste sample. This technique allows a sample to be pretreated and measured in a few minutes instead of hours or days using other methods.
Branch recently received her doctorate from the University of Cincinnati and works at PNNL, which is working to enhance the sensitivity of this detection method.
Source: U.S. Dept. of Energy, Office of Environmental Management
