Real-Time Quantification of Hydrogen and Deuterium Using Laser-Induced Breakdown Spectroscopy (LIBS) in the Off-Gas...

Laser-induced breakdown spectroscopy (LIBS) is being considered for elemental analysis of radionuclides transported into the off-gas system of molten salt reactors. A mobile LIBS system was calibrated for gas-phase measurements of hydrogen (i.e., protium, denoted here as H) and deuterium (D) in argon (Ar). The system was then used to quantify the concentrations of H and D in the off-gas of an engineering-scale molten salt loop (∼200 kg salt) following the addition of H₂ or D₂ as a 4% blend in Ar. The limits of detection for H and D were determined to be 0.0013 and 0.0011 mol% (13 and 11 parts per million), respectively. This research was carried out at the U.S. Department of Energy's Oak Ridge National Laboratory in the Facility to Alleviate Salt Technology Risks (FASTR) pumped salt loop. Previous molten salt LIBS research has predominantly been performed at the bench scale, thus this study represents a major stride toward deploying LIBS technology for monitoring the performance of molten salt reactors. During the FASTR testing, the LIBS system operated continuously for several days. This online monitoring campaign demonstrates advancement in the application of LIBS for online monitoring of off-gas in molten salt systems.