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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.

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Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro-refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro-refining is carried out in the molten lithium chloride-potassium chloride (LiCl-KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl-KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl-KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X-ray mappings of the cross-section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.

Plasma sprayed yttria stabilised zirconia/NiCrAlY thermal barrier coatings proposed for molten LiCl-KCl salt environments contain pores and microcracks that may cause corrosion of the substrate on prolonged exposure. In the present work the as sprayed samples were laser remelted with various scan speeds of 1, 2?5 and 5 mm s 21 to reduce the segmented cracks. Microstructural inhomogeneities like pores and voids have been eliminated on laser remelting, however, segmented cracks were formed irrespective of scan speed. Distinct interface separating fine and coarse grains were observed at all scan speeds. The microhardness of the glazed surface improved and surface roughness was reduced. The beneficial non-transformable tetragonal phase was formed after laser remelting while the as sprayed coating consisted of insignificant monoclinic phase. An attempt was made to seal the pores of the zirconia coating by applying ZrO 2 and ZrO 2 z SiO 2 powder.