Corrosion Behavior of Candidate Materials in Molten LiCl-KCl Salt Under Argon Atmosphere

Pyrochemical reprocessing involves the use of molten LiCl-KCl (lithium chloride-potassium chloride) eutectic salt at 773 K for the recovery of uranium and plutonium from spent metallic fuel of fast breeder reactors. The materials selected for such corrosive environments should withstand high temperatures and at the same time offer good corrosion resistance. The present work discusses the corrosion behavior of candidate materials like 2.25Cr-1Mo steel (UNS K21590), 9Cr-1 Mo steel (UNS K90941), Ni-based alloy 600 (UNS N06600), Ni-based alloy 625 (UNS N06625), and Ni-based alloy 690 (UNS N06690) in molten LiCl-KCl eutectic salt at 873 K for various durations under ultrahigh-purity argon atmosphere. Corrosion behavior of partially stabilized zirconia (PSZ) coating on candidate materials also was evaluated. Weight-loss results indicated that the corrosion resistance of the materials increased in the following order: 2.25Cr-1Mo > 9Cr-1 Mo > Ni-based alloys > PSZ coating. PSZ-coated specimens showed better corrosion resistance in molten LiCl-KCl salt when compared with uncoated specimens; however, accidental ingression of oxygen and moisture could result in premature spallation of the coating. Scanning electron microscopy (SEM) examination and grazing incidence x-ray diffraction (GIXRD) analysis of exposed Cr-Mo steels and Ni-based alloys exhibited dealloyed surfaces and corrosion product regions rich in Cr, indicating preferential leaching of Cr. The paper highlights the results of the present investigation.