Monitoring for Process Control using Visible, Near-Infrared, and Raman Spectroscopy
Figure 2. Sensor fusion design: schematic of a flow cell combining absorbance (UV−vis and NIR) and Raman spectroscopy to monitor a process stream for multiple analytes.
Figure 2 in practice, with Raman probe provided by Spectra Solutions Inc.
This study (ACS Sens. 2020, 5, 2467−2475) demonstrates the use of sensor fusion, combining visible, near-infrared (NIR), and Raman spectroscopy, for real-time, on-line monitoring of complex nuclear fuel reprocessing streams. The study focuses on quantifying key analytes like plutonium (Pu), uranium (U), neptunium (Np), and nitric acid (HNO₃) in highly challenging environments. Raman spectroscopy plays a critical role in this multimodal approach, particularly for identifying and quantifying species such as U(VI) and HNO₃, which exhibit distinct Raman fingerprints (Figure 3). The technique's ability to provide molecular-specific information, even in the presence of overlapping spectral features from other components, makes it indispensable for accurate real-time analysis.
Figure 3. Spectral fingerprints for Pu in its three observed oxidation states for the three different forms of spectroscopy utilized. Pu varied from 0 to 30 mM, nominally at 1 M HNO3, except for Pu(VI) at 3 M HNO3.
Figure 4. Species concentrations calculated by models over the course of a CoDCon run (stripping section)
Utilizing Raman spectroscopy has unique advantages, including aspects like its sensitivity to oxidation states and speciation, which are crucial for monitoring nuclear fuel recycling processes. For instance, Raman was used alongside UV-vis and NIR to validate results and overcome limitations of single-technique approaches (Figure 2). Chemometric models, applied to the spectral data, enabled real-time process control, as shown in the real-time output of species concentrations (Figure 4). The success of this sensor fusion approach, with Raman as a key component, represents a significant advancement in monitoring harsh chemical environments, reducing reliance on hazardous grab sampling, and improving the efficiency and safety of nuclear fuel reprocessing. The ability to detect short-lived species and process deviations (Figure 6) further underscores Raman spectroscopy's value in dynamic industrial applications.
Figure 6. Percent composition of U and Pu in the aqueous product
stream in runs 1(A )and 2(B). Both plots use the legend in (B).
Publication:
Amanda M. Lines, Gabriel B. Hall, Susan Asmussen, Jarrod Allred, Sergey Sinkov, Forrest Heller, Neal Gallagher, Gregg J. Lumetta, and Samuel A. Bryan, "Sensor Fusion: Comprehensive Real-Time, On-Line Monitoring for Process Control via Visible, Near-Infrared, and Raman Spectroscopy," ACS Sensors 2020 5 (8), 2467-2475