Molten Salt Corrosion and Its Mitigation for Pyrochemical Reprocessing Applications

Abstract

Pyrochemical reprocessing has opted for the reprocessing of spent metallic fuels from future sodium-cooled fast breeder reactors in India. Pyrochemical reprocessing involves several unit operations with various atmospheres at different temperatures ranging from 500 to 1500 °C. The primary separation process of the pyrochemical reprocessing is the electrorefining step. The electrorefining process uses molten LiCl–KCl eutectic salt as the electrolyte at 500 °C under an inert atmosphere for the separation of the fuel elements from spent fuel. Molten salts at high temperature are more corrosive to the structural materials. Hence, structural materials should possess high corrosion resistance in molten salt. Recent corrosion evaluation of various structural materials like stainless steels, Cr–Mo steels, Ni-based alloys, and graphite carried out was investigated in molten salt system. The possible and various types of corrosion mitigation strategies have adopted and test protocols for the molten salt corrosion protection are discussed. Thermal spray ceramic coatings as one of the best chemical barriers for the protection of materials from molten salts are highlighted. The mechanism of molten salt corrosion, the corrosion resistance behaviour of various candidate structural materials in LiCl–KCl molten salt, its mitigation by providing ceramic coatings for pyrochemical reprocessing applications are briefly discussed. All the structural materials tested in LiCl–KCl are found to be corrosive and the ceramic coated materials showed excellent corrosion resistance in the molten salt atmosphere.