Monitoring Noble Gases (Xe and Kr) and Aerosols (Cs and Rb) in a Molten Salt Reactor Surrogate Off-Gas Stream Using Laser-Induced Breakdown Spectroscopy (LIBS)

Abstract

This study with surrogate materials shows that laser-induced breakdown spectroscopy (LIBS) is a robust tool with promising capability toward monitoring gaseous (Xe and Kr) and aerosol (Cs and Rb) species in an off-gas stream from a molten salt reactor (MSR). MSRs will continually evolve fission products into the cover gas flowing across the reactor headspace. The cover gas entrains Xe and Kr gases, along with aerosol particles, before passing into an off-gas treatment system. Univariate models of Xe and Kr peaks showed a strong correlation to concentration indicated by their coefficients of determination of 0.983 and 0.997, respectively. Multivariate models were built for all four analytes using partial least squares regression coupled with preprocessing steps including normalization, trimming, and/or genetic algorithm derived filters. The models were evaluated by predicting the concentrations of the analytes in four validation samples, in which all calibration models were successfully validated at a confidence interval of 99.9%. Lastly, pressure controllers were used to regulate the mass flow rate of Kr flowing into the measurement cell in sinusoidal and stepwise waveforms to test the real-time monitoring capabilities of the regression models. Both univariate and partial least squares Kr models were able to successfully quantify the gas concentration in the real-time evaluation. The root mean squared error of prediction (RMSEP) values for these real-time tests were calculated to be 0.051, 0.060, and 0.121 mol% demonstrating the measurement systems’ capability to perform online monitoring with acceptable accuracy.

The effect of interfacial phenomena on gas solubility measurements in molten salts

“…Direct measurement of the analyte in the salt itself will avoid errors, by spectroscopy or radiotracers. Gas-phase measurements of noble gases have been achieved by laser-induced breakdown spectroscopy and could be applied to the liquid (Andrews et al, 2022).…”

State of Knowledge on Aerosols and Bubble Transport for Mechanistic Source Term Analysis of Molten Salt Reactors

“…This technique has been demonstrated with molten salt aerosol systems, namely, to determine the elemental composition of aerosols formed from CeCl3-LiCl-KCl and UCl3-LiCl-KCl systems [52,54]. LIBS has also recently been employed to quantify noble gases, alkali metals, and lanthanides in surrogate MSR off-gas streams and is a promising technique for on-line monitoring of MSR off-gas [111,112]. Multielement aerosol streams may yield interference in the elemental signatures in the LIBS spectrum.…”

Concept for an irradiation experiment to test a laser-induced breakdown spectroscopy off-gas sensor for molten salt systems

“…For the first capability, optical spectroscopy has been proposed as a strategy for remotely monitoring an off-gas system (Hughey et al, 2020;Andrews et al, 2021b;Felmy et al, 2021;Andrews et al, 2022a;Andrews and Myhre, 2022). There are multiple forms of optical spectroscopy that, when coupled, can provide a molecular, elemental, and isotopic fingerprint in real time.…”

“…To study the release characteristics, a LIBS sensor will be installed inline to monitor the elemental composition of released gases, vapors, and aerosols. The LIBS sensor has been demonstrated on fission product relevant aerosols and noble gases in an idealized system; however, it has not yet been tested on irradiated salts to assess the effects of radiolysis on the equipment or analysis (Andrews et al, 2022a;Andrews and Myhre, 2022).…”