Development of an absorption spectroscopy probe for in situ monitoring of dissolved impurities in molten salts

Molten salts, as an advanced heat transfer fluid, have attracted significant research attention in recent years due to their potential in addressing global energy challenges. This paper outlines the development of an optical probe that can be integrated with high temperature molten salt systems to monitor changes in dissolved species using UV-VIS-NIR absorption spectroscopy. The probe offers safe optical access into salt melts through chemically compatible viewports built within rigid tubing that can be easily integrated with salt reservoirs with minimal modifications to test setups. This marks a significant step towards real time optical sensing in molten salts to study salt chemistry and corrosion of structural components under dynamic conditions. Several steps involved in designing, fabricating and testing the probe prototype in molten fluoride melts (FLiNaK - 46.5\% LiF-11.5\% NaF-42\% KF) are presented along with test results on estimating composition of multi-species salt mixtures over short and long duration tests.