An Instrument Established for the High Temperature Measurement of Ultraviolet-Visible Absorption Spectra of Molten Fluoride Salt Behaving As Coolant in the Molten Salt Reactor

Molten salts were widely used in nuclear and solar power field due to the excellent heat transfer and storage. Molten fluoride salts were selected as primary and secondary coolants in the Molten Salt Reactor Experiment (MSRE) developed by Oak Ridge National Laboratory (ORNL). Therefore, it is dramatically important to study the physical and chemical properties of molten fluoride salts that impact on the design of reactor core and thermohydraulics. The molecular structure directly determines the physical and chemical properties of matter, so it is also essential to study the structure of molten salts. Spectroscopy has been proven to be a very useful tool for investigating molten salts structures. However, the standard instrument is inapplicable for measurement of the high temperature molten salts, especially for molten fluoride salts. To obtain the ultraviolet-visible (UV-Vis) absorption spectra of molten salts at high temperature, an instrument was designed to study the structures of molten salts in situ. The instrument is mainly composed of a vertical pit furnace connecting with a glovebox and an assembled cuvette which can operate from room temperature up to 800°C. The assembled cuvette is made of Hastelloy C/N as the main body with a reverse ‘T’ contour and diamond or crystalline CaF₂ etc. as the window plates, so it can withstand the corrosion produced by the sample and allow the interest light passing through. The effective spectral range of this instrument is from 200 to 1000 nm. Performances of the instrument are testified by spectral studies on water under room temperature and molten salts under high temperature.