(351a) Development of an Infrared Measurement Method for Molten Fluoride Salt

Molten fluoride salts have been proposed as both coolant and/or fuel solvent in advanced nuclear reactor designs. In order for these designs to be commercially viable, chemistry control systems must be developed, due to the extremely corrosive behavior and high melting temperature of these salts. Critical to these systems will be the ability to detect and calculate activities of melt species. In principle, an infrared spectrometer could perform this task, through correlation of peaks with vibrational modes of various complex species. In addition, the high temperatures and large thermal gradients that are present in some designs could lead to situations where radiative heat transfer (RHT) would be a significant heat transfer mechanism. In order to model RHT accurately, precise infrared measurements must be made to determine the spectral absorption coefficient of the melt of interest. We are working to develop emission and reflection infrared measurement techniques, using a commercial high-temperature cell and reflection accessory. Preliminary data has been obtained and validated for solid reference materials, including fused SiO₂ (silica) and crystalline Al₂O₃ (sapphire). A preliminary design has been generated of a custom sample holder which will fit in the cell to minimize both the curvature of the salt surface and the degree to which the detector sees radiation from the sample container walls. Future work will include low-temperature measurements of solid LiF and FLiNaK, development of a gas phase control system, and high-temperature measurements of molten FLiNaK.