The Effect Study Of Corrosion Product CrF₃on Physico-chemical Properties Of LiF-NaF-KF

Shanghai Institute of Applied Physics was involved in the project of Thorium Molten SaltReactor, one of the strategic priority science and technology research programs of ChineseAcademy of Sciences, in2011. The accurate and credible thermo-physical properties of FLiNaK(LiF-NaF-KF:46.5mol%-11.5mol%-42mol%) are very important parameters for design ofthermo-technique，hydraulics and reactor core as well as safety of reactor because it has beenselected as candidate coolant of secondary loop for molten salt reactor(MSR). Consequently, thecompatibility of FLiNaK containing corrosion product CrF3with candidate structural materialshas been assessed in this thesis by experimental investigation and theoretical calculation.High-temperature vacuum sintering furnace, specially designed by division of molten saltchemistry and engineering, was used to prepare FLiNaK with additive various amounts of CrF3.The influnce of temperature, time and different crucibles on the preparing FLiNaK with additiveCrF3was investigated and it was found that the optimal process is800。C and50hr when6000ppm CrF3was dissolved in FLiNaK.The thermo-physical properties both of primary FLiNaK and FLiNaK with additive6000ppm CrF3, such as melting point, enthalpy change, specific heat，thermal diffusioncoefficient and density, were determined using differential scanning calorimetry, laser flashthermal constant analyzer and Archimedean method, respectively. It can be concluded that thechange of thermo-physical properties with FLiNaK containing6000ppm CrF3should benegligible within the acceptable experimental errors, except its thermal diffusion coefficient ofsolid phase samples.In order to theoretically explore the effect of CrF3on the thermo-physical properties ofFLiNaK, the comprehensive thermodynamic modeling of MF-CrF3(M=Li, Na and K) systemwas set up. The database for quaternary system of LiF-NaF-KF-CrF3was established fromextrapolation of symmetry melt (Muggianu model) within the framework of CALPHAD methodand referred to the reported data of LiF-NaF, LiF-KF and NaF-KF, meanwhile the solubility ofCrF3in FLiNaK was predicted. Considering there is a forming kinetics of Na3CrF6in thequaternary system of LiF-NaF-KF-CrF3, the calculated concentration of CrF3dissolved inFLiNaK is consistent with the data reported by ORNL.Finally, the Compatibility of primary FLiNaK and FLiNaK containing4000ppm CrF3with316LNSS, Hastelloy-N and graphite were explored respectively by thermodynamic calculation,scanning electron microscope, synchrotron X-ray diffraction, Raman spectra and laser flashanalyzer. It was found that4000ppm CrF3could increase the corrosion of316LNSS andHastelloy-N, which might induce the element Cr lost. But with graphite, it could be negligiblewithin experiment errors. All the experimental results obtained in this thesis may provide some fundamental suggestion for evaluating the compatibility of FLiNaK with candidate materials inproject of MSR.