"Deployment of Laser Induced Breakdown Spectroscopy Sensor for Molten Salt Reactor Off-Gas Stream" was presented by Hunter Andrews at Oak Ridge National Laboratory's Molten-Salt Reactor Workshop on 2021-10-13.
Enabling molten salt reactor (MSR) deployment by developing technology for off-gas analysis, why use laser induced breakdown spectroscopy (LIBS)? Elemental analysis via optical emission spectroscopy of laser induced plasmas benefits:
Little to no sample prep
Useful for solid, liquid, and gas analysis
Typical sensitivities of ppm
Quasi-nondestructive (nanograms per shot)
Can be completely fiber optic based
Design Challenges:
Producing a surrogate aerosol stream
Designing a measurement cell
Collision nebulizer was selected to generate aerosol stream for analysis.
Aerosol particle sizes range from ~1-10 μm in diameter.
Sheath gas approach was used to contain aerosol stream during measurement.
Sheath gas system successfully contained aerosol stream.
Complete prototype aerosol measurement system was manufactured.
Three representative elements selected for aqueous aerosol monitoring system were Gd, Nd, and Sm:
All act as neutron poisons in a reactor making their concentrations of interest to operators.
Concentrations ranging from 0 to 2000 ppm in liquid reservoir
2000 ppm in reservoir ≈5 ppb in aerosol stream
Regression models were developed using a set of calibration samples.
Predicted concentrations of validation samples matched ICP-OES measurements.
Performed demonstration to show the measurement system’s capability to provide real-time monitoring.
Initial concentration predictions left room for improvement.
Genetic algorithm was used to refine PLS feature selection.
Genetic algorithm filtered models showed dramatically improved results.
Krypton and xenon showed strong spectral responses.
Analytes in test samples were predicted using constructed models.
Kr concentration was successfully predicted in real-time.
In summary, we have demonstrated a LIBS capability for monitoring aerosols and gases.
Our sheathed gas measuring system allows effective measurement of the sample stream while protecting optical components.
Multiple elements were simultaneously quantified in the two studies discussed.
A genetic algorithm was used to refine a quantitative model
Both gases and aerosols were able to be monitored in real-time.
Future work involves completion of a molten salt aerosol test stand and integrating LIBS sensors with off-gas treatment systems.