Corrosion of stainless steel 316L in molten LiCl-Li2O-Li

Abstract

Exposure testing of Stainless Steel 316L was performed in LiCl-Li2O-Li solutions at 650 °C for periods of 500 and 1000 h to investigate the effect of metallic Li on corrosion of materials used to contain the LiCl-Li2O electrolyte for the electrolytic reduction of used nuclear fuel. Melt compositions studied consisted of LiCl containing 1 or 2 wt% Li2O and 0, 0.3, 0.6, or 1 wt% Li. Post exposure surface analysis was performed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Focused ion beam and mechanical cross sections of the samples and gravimetric analyses were performed to determine the time-averaged corrosion rate for each sample. Lithium metal induced attack rates were found to be as high as 2.91 mm/y. In the absence of solvated Li in the LiCl-Li2O system, LiCrO2, Li2CrO4, and NiFexCr2-xO4 were observed to be the primary corrosion products. When Li was present in the melt, the oxidized alloying elements were only detectable via X-ray photoelectron spectroscopy, and the surface was primarily comprised of bare metal.