EXPRESS: Real-Time Quantification of Hydrogen and Deuterium Using Laser-Induced Breakdown Spectroscopy (LIBS) in the Off-Gas of an Engineering-Scale Pumped Molten Salt Loop

Laser-induced breakdown spectroscopy (LIBS) is being considered for elemental analysis of radionuclides transported into the cover 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 H 2 or D 2 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 Risk (FASTR). Previous molten salt LIBS research was predominantly performed at the bench scale, so this study was 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.