High-temperature gas-cooled reactors (HTGR) are attractive for future power generation due to their inherently safe design, high power conversion efficiency, and potential to also deliver high-temperature process heat. With consideration for commercial deployment, the safety and structural integrity of HTGRs are being investigated under accident conditions. The focus of this project is on the short-term phenomena induced by steam ingress following a steam generator heat-exchanger tube rupture (SGTR). This research aims to develop a tunable diode laser absorption spectroscopy (TDLAS) system capable of taking steam measurements (concentration, temperature, pressure) within the lower plenum and core of a 1/8th scaled HTGR simulator to provide the experimental data needed to validate predictive CFD models for steam ingress.TDLAS is a non-intrusive, non-perturbative line-of-sight diagnostic technique that can be used to recover gas concentration, temperature, and pressure via the Beer-Lambert law. Three distributed feedback (DFB) laser wavelength ranges that probe specific H2O absorption transitions are selected based on absorption spectra simulation using the HTGR simulator environment (T = 300 - 1000 K, P = 0.1 - 0.3 MPa, [H2O] = 0.0-1.0, x 3-10 cm, where x is the path length of sensing). A data analysis algorithm that uses a least squares Voigt spectral fitting routine has been developed to simultaneously recover water vapor concentration, temperature, and pressure at a measurement rate of 100 Hz. The analysis code also enables solving for spectral parameters (linestrength and broadening coefficients), which has been used to calibrate the diagnostic technique. Within the calibration test section environment of T = 497 - 697 K, P = 1 - 2 atm, and XH2O 7 - 85 %, the TDLAS system is able to achieve accuracies and precisions (acc. ± prec.) of T < 4.4 ± 2.8 %, P < 19.0 ± 5.0 %, and XH2O < 23.1 ± 3.8 % compared to sensor data by combining the performance of each laser pair (DFB7203 and DFB7306/DFB7451). High temperature fiber optics and custom launching/receiving optics have been designed, developed, and tested for in-situ launching/receiving capability at 673 K, 100 K higher than in reviewed literature, with ability to reach up to 1000 K.
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