Using X-ray Absorption Spectroscopy (XAS) and Raman spectroscopy, salt mixtures of chloride (5 mol% SrCl2 in NaCl) and fluoride (5 mol% ZrF4 in LiF) were investigated for speciation, radial distances, and coordination numbers to provide support for the development of molten salt nuclear reactors. Both salt mixtures were studied in temperature increments up to 1,100 °C and again when resolidified. Measurements were taken for the salts with and without boron nitride powder as a diluent. Strontium’s first shell was observed to be coordinated with chlorine (Sr2+-Cl-) and Zirconium’s first shell was coordinated by fluoride (Zr4+-F-), both having coordination numbers that decrease with increasing temperature. Multiple zirconium complexes were believed to be present in the melt, resulting in an anomalously low Zr first shell coordination number measured by EXAFS. The use of BN powder was found to be a tenable diluent for future uranium containing salt mixtures.

Local structure of NaCl-SrCl2 and LiF-ZrF4 molten salts by X-ray absorption spectroscopy and Raman spectroscopy

ACS Fall 2021

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