PNNL

Abstract

Molten hydroxide scrubbing of off-gas vapors is a crucial technology to enable operation of Generation IV molten salt nuclear reactors (MSRs). Operation of MSRs offer several inherent safety features compared to other reactors such as a homogenous fuel composition, low vapor pressures, operating at atmospheric pressure, and online refueling. MSRs produce off-gases which can be vented by the reactor core and treated via off-gas scrubbers. Molten hydroxide scrubbers focus on capturing volatile iodine radionuclides. The performance of these scrubbers will depend on the chemical interactions of the scrubbing medium and the off-gas species. Knowledge of the concentration and speciation of scrubbed or captured species as well as process and envi-ronmental interferents can enable advanced operation of MSR off-gas treatment systems. Optical online monitoring is an excel-lent technology to provide this information in real time while limiting the need for operators to interact with radioactive sam-ples. Raman and UV-vis 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 in the molten phase of a NaOH-KOH eutectic and construct a calibration curve of the Raman signal. Additionally, a carbonate inter-ferent is followed from the gas phase to the liquid phase as a basis for reaching a Raman-aided mass balance of the molten hy-droxide eutectic scrubber system.