Corrosion of anode materials during direct electrolytic reduction of uranium oxide in molten LiCl-Li2O

Abstract

Direct electrolytic reduction of UO2 in LiCl-Li2O was performed with a platinum anode surrounded by a mesh shroud. The anode shroud was comprised of three pieces; shaft, cage and screen. The shaft and cage were made of Haynes C2000 and the screen was made of Hastelloy C276. Five reduction tests were performed sequentially with the same anode/shroud set, while two other reduction tests did not use an anode shroud. Based on mass measurements, the average rate of platinum loss from corrosion was determined to be 1.69 µm/hr. It was confirmed with X-ray diffraction that a layer of lithium platinate forms on the surface of the anode. The anode shroud was found to increase the anodic potential by 0.25 V. After each test, a corrosion coupon was removed from the Haynes C2000 anode shroud and analyzed via scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Salt samples were taken after each test and analyzed using inductively coupled plasma mass spectrometry. The results indicated that nickel, chromium, and molybdenum were all depleted from the Hastelloy C276 shroud and accumulated in the molten salt. SEM-EDS line scans were used to estimate linear corrosion rates. Based on nickel, chromium, and molybdenum, the shroud corrosion rates were determined to be 0.36, 0.49, and 0.51 µm/hr, respectively.