To monitor the concentration of Ni corroded into the molten salt, the height of the raw intensity of the Ni K-edge step needed to be determined from the XANES spectra. We fitted the pre-edge with a linear function and the post-edge with a cubic (or quadratic) function. The edge step size is the difference in intensity between the refinements at a chosen point in the energy spectrum; the same point was used to compare between different spectra. This procedure is shown in Fig. with fits to the pre-and post-edge regions to calculate the size of the step. The step height is directly related to the concentration of Ni in the sample . However, comparing the pure FLiNaK calibration spectrum with a corrosion spectrum displayed in Fig. , they not only have different shapes but have vastly different intensities. This is due to the different detectors used for each experiment; the calibration measurements used a PIPS detector, while the corrosion measurements were performed with an SDD detector outside a furnace. The furnace increases the distance between detector and sample, and thus decreases the fluorescence signal. As such, the spectra of known concentration required modification to be comparable with the spectra captured during corrosion experiments.