Electrochemical and spectroscopic study on corrosion behavior of Ni-based alloys in chloride melts: Materials for an integral molten salt fast reactor

For the long-term operation of integral molten salt fast reactor safety, it is necessary to select structural materials with high corrosion resistance such as Ni-based alloys in high-temperature chlorides of specific composition. In this study, the corrosion behavior of Inconel 600, Inconel X750, Hastelloy C-276, and Incoloy 800, which are the candidates for the structural materials in NaCl-KCl-MgCl2 melt at 723 K and NaCl-CaCl2 melt with CeCl3 or LaCl3 at 873 K were investigated by electrochemical and spectroscopic analyses toward designing materials used in the integral molten salt fast reactor. The corrosion rates were estimated based on the elemental analysis of alloy surfaces by glow-discharge optical emission spectroscopy and the corrosion current density by linear polarization technique. It was found that the trend of corrosion rate for each alloy changed significantly depending on the composition of the chloride melts. The electrochemical behavior obtained from the linear polarization measurement and the impedance spectroscopy indicated that the cathodic reaction during the corrosion process was different among each melt. To discuss the effect of molten salt composition on corrosion behavior, the melt structure was investigated by high-temperature Raman spectroscopy and density functional theory calculation. The results indicated that the coordination structure of oxide ions, which are corrosion products formed in the cathodic reaction, changed depending on the composition of the chloride melts. The reported data show that it is important to control the corrosion process by clarifying the structure of each melt in order to select a highly compatible system of molten salt and structural material.