Iodine and Carbonate Species Monitoring in Molten NaOH–KOH Eutectic Scrubber via Dual-Phase In Situ Raman Spectroscopy

Abstract

Molten hydroxide scrubbing of off-gas vapors is a potential process to improve safety during the operation of generation IV molten salt nuclear reactors (MSRs). MSRs produce off-gases that can be vented by the reactor core and treated via off-gas scrubbers. Molten hydroxide scrubbers focus on capturing volatile iodine radionuclides, and they can also be used to capture aerosols and particulates and to neutralize acidic species. The performance of these scrubbers depends on the chemical interactions of the scrubbing medium with the off-gas species. Knowledge of the concentration and speciation of scrubbed or target species, as well as process and environmental interferents, can enable advanced operation of MSR off-gas treatment systems. Optical online monitoring is an excellent technology to provide this information in real time, while limiting the need for operators to interact with radioactive samples through hands-on interrogation. Raman spectroscopy can provide crucial chemical information on the state of the molten eutectic during treatment in the molten phase, as well as the gas phase. In this work, Raman spectroscopy is used to detect iodine species, specifically iodate, in the molten phase of a NaOH−KOH eutectic and to construct a calibration curve of the Raman signal of those species. Additionally, a carbonate interferent is followed from the gas phase to the liquid phase as a basis for reaching a Raman-aided mass balance of the molten hydroxide eutectic scrubber system.

In Situ Raman Methodology for Online Analysis of CO2 and H2O Loadings in a Water-Lean Solvent for CO2 Capture

“…While we have not developed models for other amine-based carbon-capture solvents, we are certain that would be possible and is currently planned. The techniques demonstrated in this manuscript are amenable to other systems, as have been amply demonstrated by our research group efforts in a variety of processes including online monitoring of nuclear waste streams, nuclear fuel reprocessing streams, ,,− and strong and weak acid solutions streams. ,,− …”

The effect of interfacial phenomena on gas solubility measurements in molten salts

“…Another approach is to monitor absorption actively in a molten salt, that is, well stirred by a sparge of the analyte in a carrier gas. If the analyte has an appropriate spectroscopic signature, then these measurements can be performed on the salt in situ because the carrier is often optically transparent (Medina et al, 2022). Thermogravimetry tracks increases in salt mass as a gas mixture carrying the analyte contacts the salt (Bratland and Corbett 1966).…”

Densification and Immobilization of AgI-Containing Iodine Waste Forms Using Spark Plasma Sintering

“…Radioiodine management is an important topic due to human health concerns associated with uncontrolled releases during nuclear accidents, , controlled releases during used nuclear fuel reprocessing, , and capture from the off-gas systems in molten salt reactors. − Many different capture technologies have been explored under a wide range of processing conditions and environments by the U.S. Department of Energy for evaluating radioiodine management. These technologies mainly include the utilization of caustic scrubbers and solid sorbents, ,,− the latter category largely encompassing approaches for utilizing the strong chemisorption between iodine and silver to form AgI.…”