Optical Basicity Determination of Molten Fluoride Salts and its Influence on Structural Material Corrosion

For this research, the focus is on FLiNaK and FLiBe salts in two conditions of relevance to FHRs and MSRs: (i) eutectic and off-eutectic pure fluoride salts, and (ii) eutectic pure fluoride salts similar to (i) but containing lanthanide fluorides. Three main research tasks will take place. In task 1, the optical basicity of different molten fluoride salts including eutectic, and off-eutectic, FLiNaK and FLiBe, with and without addition of lanthanide fluorides, will be measured using ion probes at different temperatures. UV-Vis spectroscopy is used for the determination of optical basicity parameters and the correlation between optical basicity and salt chemical composition will be derived based on the obtained data. In task 2, the speciation and structure of the molten fluoride salts studied in task 1 will be analyzed by synchrotron XANES/EXAFS at the National Synchrotron Light Source II (NSLS-II) to set up the connection between salt composition, optical basicity, speciation, and structure of molten salts. In task 3, a few typical molten fluoride salts with different optical basicity studied in task 1 will be selected as the electrolyte for isothermal corrosion experiment. A spectro-electrochemistry test cell will be designed for quantitative measurement of dissolved corrosion products to achieve the in-situ corrosion monitoring during the corrosion experiment. The post-corrosion samples will also be analyzed by a suite of characterization analysis.

The goals of this research project are to:

  • Develop a scale of optical basicity for different fluoride salts used in Molten Salt Reactors (MSR) and Fluoride salt-cooled High-temperature Reactors (FHR)
  • Understand the relationship between molten salt structure and its optical basicity
  • Understand the influence of optical basicity on the corrosion behavior to structural materials in reactors
  • Connect salt composition, optical basicity, and salt structure to understand their governance on overall corrosive properties of molten fluoride salts

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