Enhanced monitoring of fuel reprocessing relies on machine learning

November 8, 2021, 9:30AMNuclear News



Two student interns at Pacific Northwest National Laboratory looking for an easier way to monitor the acidity and phosphate concentrations of a process fluid like dissolved nuclear fuel have published research on a monitoring method that provides real-time data without the need for physical sampling of the substance. Their story was published on October 27 on PNNL’s website.

Student leaders: Hope Lackey conducted pH measurement and chemical analysis research during her Science Undergraduate Laboratory Internships (SULI) experience at PNNL in 2018 while she was working toward her undergraduate degree in environmental studies at the College of Idaho. Andrew Clifford, also a SULI intern and a student at the College of Idaho, partnered with Lackey between his junior and senior year, while studying for a dual bachelor’s in chemistry and math/physics.

The students worked under the mentorship of Sam Bryan, a chemist and Laboratory Fellow at PNNL who leads PNNL’s efforts in real-time testing and continuous monitoring. Their research was published in two recent Analytical Chemistry journal articles. Lackey and her co-authors tackled complex chemical systems like Hanford tank waste and radioactive solutions in Reimagining pH Measurement: Utilizing Raman Spectroscopy for Enhanced Accuracy in Phosphoric Acid Systems.

Hope Lackey performs research to observe and control pH during chemical processing in PPNL’s Radiochemical Processing Laboratory. (Photo: Hope Lackey/PNNL)

Going on line: The pH level and chemical structure of dissolved nuclear fuel must be monitored to ensure and improve the safety and efficiency of reprocessing. Traditional off line lab analyses can test a solution sample, but manual collection exposes a worker to a potentially hazardous solution, and each sample can represent the solution only at the point in time it was retrieved.

The research team’s remote, on line technique measures the interaction of light with chemical bonds using an analytical technique called Raman spectroscopy. In contrast to traditional probes, Raman probes are physically robust and can function for extended periods in harsh environments, according to PNNL.

“Basically, instead of manually dealing with these caustic solutions, we’re adapting robust probes to shine an intense light on solutions,” Lackey said. “But the ‘camera’ we use doesn’t make colored images. It gives us ‘pictures’ in real time to record the solution’s response to light.”

The approach also used chemometrics—the application of machine learning to chemistry—to create an algorithm to convert that spectral response into a measure of acidity in real time and, according to PNNL, yield more rapid and cost-effective results.

One step further: The second journal article, which was given cover status in Analytical Chemistry, is titled Raman Spectroscopy Coupled with Chemometric Analysis for Speciation and Quantitative Analysis of Aqueous Phosphoric Acid Systems.” The paper describes using the same technique to measure a different parameter: the concentrations of phosphates. Under different levels of acidity, phosphate can take four chemical forms based on proton removal. Clifford and Lackey’s technique quantifies each type of phosphate and the total phosphate, at any pH. That measurement guides initial separations of the chemical to ensure that phosphates do not interfere with overall processing.

Implications: Although the two papers cover potential benefits specific to nuclear waste processing, Amanda Lines, a chemist in PPNL’s Radiochemical Processing Laboratory, notes, “These approaches align well with PNNL’s mission around energy and environmental cleanup and help us maintain our position as leaders in on line monitoring research, but what I find compelling are the possibilities to improve how other chemical processes are deployed, outside of nuclear. Many commercial and industrial processes requiring quality control would benefit from quick and easy pH measurement and phosphoric acid detection—things like fertilizers and pharmaceutical drugs.”

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