Laser absorption spectroscopy for xenon monitoring in the cover gas of sodium cooled fast reactors

Abstract

Xenon is a fission product of uranium that must be monitored on line and in real time in the cover gas of a sodium cooled fast neutron reactor (SFR) for safety reasons. In this paper, tunable diode laser absorption spectroscopy is applied to quantify low concentrations of natural xenon in argon. Optical detection is carried out at 12 145 cm⁻¹ (823 nm) from the 6s[3/2]⁰₂ Xe electronic metastable state, populated in a low pressure DC glow discharge. Optimal discharge parameters (110 Pa, 1.3 W) were experimentally determined to maximize the laser absorption signal. Measurement stability, argon pressure spectral broadening, isotope quantification, and linearity of the optical measurement with respect to the xenon concentration in the gas sample were carefully investigated. Under optimized experimental conditions, the detection limit of xenon over argon molar ratio is estimated as 60 ± 10 parts per billion at 1 Hz, corresponding to a xenon number density of 1.6 × 10⁹ atoms.cm⁻³ along the laser beam.