Combined Spectroscopic Techniques for Real-Time Monitoring of Turbid Molten Salt Systems for Integrated Fuel Cycle Solutions

Accurate monitoring of molten salt systems is critical for operational safety, efficiency, and regulatory compliance. These systems often contain special nuclear materials in chloride or fluoride forms, which can form oxides and oxyhalides when exposed to water or oxygen. Insoluble actinide oxides such as uranium oxide (UO₂) create heterogeneous, turbid salts that complicate material accountancy. Traditional electrochemical methods like voltammetry are ineffective for quantifying these species, highlighting the need for advanced characterization techniques. To address this challenge, we developed a combined spectroscopic approach integrating UV-Vis transmission, diffuse reflectance, Raman, and fluorescence spectroscopy. This suite enables simultaneous monitoring of soluble and insoluble species across phases, providing real-time insights into oxide formation and salt composition. Proof-of-concept studies using lanthanide chlorides and oxides as surrogates demonstrated that these techniques can successfully probe heterogeneous systems. UV Vis quantified dissolved species, while diffuse reflectance and Raman/fluorescence detected and quantified suspended oxides, even in turbid environments. The ability to monitor both phases in real time represents a significant advancement for nuclear safeguards and process control. Ongoing work will extend these techniques to actinide-bearing molten salts at high temperatures, with the goal of establishing robust calibration protocols and in-situ monitoring capabilities. This approach has the potential to enhance the commercial viability of molten salt reactors and reprocessing facilities by improving nuclear material accountancy and supporting criticality safety, nuclear safety, and nonproliferation measures.