Advancing Optical Spectroscopic and Chemometric Approaches to Solve Key Analytical Challenges in the Nuclear Fuel Cycle

Hope E. Lackey

doi:10.7273/000007165

To close the nuclear fuel cycle, innovative work in the development and scaling up of spent fuel recycling schemes is necessary. Spent fuel and legacy waste reprocessing must be undertaken and processing efforts accelerated to reduce current inventories of material in interim storage and to improve the environmental sustainability of nuclear reactor fuel production. This work contributes to the growing body of research dedicated to the demonstration of optical spectroscopy as a robust, trusted tool for real-time monitoring and characterization of chemical systems in the nuclear fuel cycle. Specifically, this work focuses on promoting the reduction of grab sampling from radioactive material process streams in three ways. Firstly, by providing real time data for chemical systems, on-line monitoring has been demonstrated to reduce the required number of grab samples required to maintain safeguards standards. A major challenge for optical absorbance techniques during process monitoring is the acquisition of a stable spectral reference. The analysis of single-beam spectra for the prediction of lanthanide concentration is explored under instrumental conditions causing tenfold changes in incident light for the optical measurements, and robust linear models are produced from these unreferenced, visible range spectra. This method promotes the use of single-beam spectroscopy as a real-time measurement tool even in on-line, hazardous, and physically inaccessible systems, such as those found in nuclear fuel reprocessing or legacy waste processing. Secondly, the use of optical spectroscopic techniques for measurement on microfluidic devices (MFDs) is explored. MFDs require much smaller sample volumes compared to traditional optical measurement cells, and therefore their increased use in nuclear material characterization could reduce the required volume for grab samples. Thirdly, the use of sensor fusion can provide increased quantitative and qualitative information from a single sample. Sensor fusion involves the application of multiple measurement methods simultaneously to a single sample; the data streams from each method may be analyzed separately or together. In this work, up to three nondestructive optical techniques, Vis and NIR absorbance and Raman spectroscopy, are utilized to interrogate lanthanide and actinide samples. By combining spectral data streams, quantitative errors of prediction are improved and trends in speciation are revealed. The overarching goal of this work is to advance chemometric data analysis of optical spectra in challenging measurement systems, analyzing chemically complex samples on the microfluidic scale and under measurement scenarios encompassing substantial spectral variance. The multivariate analysis schemes developed here focus on analyzing three datasets of f-element solutions using multiple chemometric techniques to derive both qualitative and quantitative information for enhanced characterization of the target systems. It lays the groundwork for future applications of optical spectroscopic techniques on the next generation of microfluidic platforms and for deployment of optical spectroscopic techniques in challenging on-line monitoring scenarios.

Advancing Optical Spectroscopic and Chemometric Approaches to Solve Key Analytical Challenges in the Nuclear Fuel Cycle

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