Corrosion Behavior of Structural Materials in LiCl-KCl Molten Salt by Thermogravimetric Study

Spent metallic fuel from future fast-breeder reactors would be processed by non-aqueous pyrochemical reprocessing. Different unit operations of pyrochemical reprocessing demands various structural materials that are compatible with molten salt medium at high temperatures. In the present study, the corrosion behavior of the candidate materials stainless steel (SS) 410, alloy 600 and 9Cr-1Mo (9% chromium and 1% molybdenum) steel was investigated in molten lithium chloride–potassium chloride (LiCl-KCl) salt by thermogravimetric studies under inert and reactive atmospheres. The test specimens, along with molten salt, were isothermally heated at 500 and 600°C for 24 h in both atmospheres. Alloy 600 showed marginally higher weight gain than 9Cr-1Mo and SS410 under both atmospheres at 600°C. Higher weight gain was observed under reactive atmosphere than in inert atmosphere at 600°C. All of the samples investigated under both atmospheres at 500°C showed insignificant weight loss. The surface morphology and energy dispersive x-ray spectroscopy (EDS) analysis revealed the formation of porous corrosive layers all over the surface with Cr-depleted and Cr-rich regions. The laser Raman spectroscopy (LRS) analysis confirmed the formation of a lithium chromite (LiCrO₂) layer in all the alloys and formation of iron (Fe) and Cr oxides along with spinel peaks. The attack by molten salt was observed to be more in 9Cr-1Mo steel than in SS410, followed by alloy 600 under both atmospheres.