Real-time, in situ (otherwise referred to as on-line) monitoring of the elemental and isotopic compositions of molten salts via laser induced breakdown spectroscopy (LIBS) and laser ablation molecular isotope spectroscopy (LAMIS) would allow for unattended near real-time nuclear material accountancy for molten salt reactors. Our approach utilizes a molten salt sampling loop in conjunction with a “windowless” gravity flow cell to enable the on-line quantitative measurement of the chemical and isotopic composition of molten salts using a LIBS/LAMIS spectroscopic system. LIBS is a non-destructive analytical technique which can provide elemental information of samples of interest that are contained under hazardous operating conditions, such as high temperatures, via remote detection of the emitted radiation following laser ablation. Similarly, LAMIS can utilize the same laser pulse to investigate the isotopic composition of the sample by looking for rotational sidebands in the spectrum from molecules that form in the microseconds after ablation. Previous LIBS/LAMIS work on molten salts used standard optical windows, typically made of diamond, sapphire, or quartz, but suffered from the agglomeration of oxides and plume deposition on said windows, drastically lowering their useful life and thus their utility for on-line monitoring applications. In this work, a windowless optical cell confines the flowing salt using a Venturi section to achieve passive coupling between the fluid pressure at the apertures and the surrounding gas pressure, rather than a window. Preliminary tests of the optical system using a static molten salt optical cell provided useful elemental information via LIBS.
Year
2024
Abstract