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 corro...

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

Corrosion of high density graphite anodes during direct electrochemical de-oxidation of solid oxides in molten CaCl 2 medium

Plasma sprayed Al2O3–40 wt% TiO2 coatings were subjected to a pulsed Nd:YAG laser melting with power densities of 640 and 800 kW/cm2 in order to minimize the surface porosity, micro-cracks, partially melted or unmelted regions, and achieving homogeneous microstructure. As-sprayed and the laser melted surface microstructure, chemical composition, microhardness and roughness were characterized by using scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Vickers hardness and profilometer. Surface morphology of a laser melted coating showed that inhomogeneities are reduced, however, network of cracks were formed irrespective of power density. Columnar growth features were observed in laser melted regions when melted with 640 kW/cm2 while these were eliminated when melted with in 800 kW/cm2 power density. Predominant β-Al2TiO5 phase was observed upon both the laser melted coatings. With an increase of laser power density, laser melted coatings exhibited considerable increase in microhardness and decrease in surface roughness due to significant reduction in the surface defects.

Surface modification of plasma sprayed Al2O3–40 wt% TiO2 coatings by pulsed Nd:YAG laser melting

Abstract Effects of different conditions during pyrolytic graphite preparation on the microstructure and density of the pyrolytic graphite have been examined. Pyrolytic graphite is obtained by pyrolysis of commercial propane gas in the deposition temperature range of 1346–2215° C at pressures of 5–200 torr and flow rates of 280–1050 cm 3 /min. The microstructure can be divided into fine regenerative, string, coarse and pebble structures which depend on the temperature and pressure, but are independent of the flow rate. These structures are closely related to the density. The density depends sensitively on the temperature and pressure and shows a minimum value in a certain condition. Three different heteromorphic phases are observed in the microstructure.

Microstructure and Density of Pyrolytic Graphite

The pyrochemical reprocessing faces challenges in the selection of suitable materials for the fabrication of the container in electro-refining process. Yttria stabilized zirconia (YSZ) coating was considered as a promising material in this application, but the performance of YSZ coating in NaCl-KCl molten salt must be improved. In the present work, metal-organic decomposition (MOD) method was put forward to deposit an Al2O3 overlay on the top surface of sprayed YSZ coating. The corrosion behavior of the YSZ coatings with and without Al2O3 overlay in molten NaCl-KCl eutectic salt was investigated by immersion test. The results showed that the sprayed YSZ coating suffered severe corrosion and a NiO corrosion product formed on the coating surface. Meanwhile, a transformation of ZrO2 from a non-transformable tetragonal (t′) phase to a monoclinic (m) phase emerged. In contrast, the surface morphology of the YSZ coating with Al2O3 overlay remained almost unchanged. No corrosion product or new phase was formed. These results proved that the Al2O3 overlay prepared by the MOD method can significantly improve the corrosion resistance of YSZ coating.

Influence of Al2O3 overlay on corrosion resistance of plasma sprayed yttria-stabilized zirconia coating in NaCl-KCl molten salt

Graphite based materials are proposed as one of the candidate materials for metallic fuel reprocessing involving high temperature molten chloride salt environment. Pyrolytic graphite (PyG) was deposited on graphite substrates by thermal chemical vapour deposition using methane gas to enhance their performance in molten chloride environments. The structural features of the PyG deposit were characterised using X-ray diffraction by measuring interlayer spacing, crystallite size and preferred orientation. The present study discusses the corrosion behaviour of PyG in molten LiCl–KCl eutectic salt at 873 K. The PyG samples tested in molten salt for 2000 h in controlled argon atmosphere exhibited negligible weight loss. The as deposited and corrosion tested samples characterised using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy showed no significant change in surface morphology. The study showed excellent corrosion resistance of PyG i...

A Nowicki

Papers

Characterisation of pyrolytic graphite exposed to molten LiCl-KCl salt