Experimental studies on interactions of molten LiF-NaF salt with some candidate structural materials for components of advanced nuclear reactors

Interaction of molten 60 LiF - 40 NaF (% mol) salt with candidate structural materials for components of advanced nuclear reactors has been studied using electron probe microanalysis (EPMA) and inductively coupled plasma atomic emission spectrometry (ICP-OES). The corrosion of structural materials (stainless steel, Ni base alloy, nickel), which was induced by the molten salt melt, has been examined in dependence on the time of exposure at operating temperature of 680 deg C. The above choice of the two analytical techniques made it possible to assess on the whole the extent of corrosion. The corrosion phenomena in structural materials were investigated using EPMA. Corrosion-released elements dissolved in solidified molten salt were determined after salt dissolution by means of ICP-OES. The LiF-NaF melt produced corrosion, which proved as a surficial modification of a structural material and a trace contamination of the melt itself. The X-ray maps by EPMA with its 1-μm lateral resolution revealed compositional changes in structural materials, such as, e. g. regular depletion of Cr in alloy A686 to the depth of 10 - 25 μm. While the lateral resolution of LA-ICP-MS with the applied laser spot diameter of 25 μm was not exactly adequate to mapping of the corroded material section and, consequently, yielded less information in comparison with EPMA, this technique was quite sufficient for the mapping of elemental content changes in solidified salt profile. Finally, nickel was proved to be the most resistant material. It was concluded that: (i) EPMA study, involving semi-quantitative elemental mapping / content profiling and detailed spot quantitative analyses makes it possible to obtain quantitative assessment of the corrosion process; (ii) qualitative profiles are provided by LA-ICP-MS, which needs further development on quantification procedure based on matched calibration samples. (author)