12 – Corrosion in Molten Salts

Molten salts have long been considered as primary coolants and heat transfer media for nuclear energy systems because of their high boiling points, volumetric heat capacities, and thermal conductivities. The high solubility of fission products in molten salts provides a greater safety margin in molten salt-based reactor concepts that employ either homogeneous molten salt fluid fuel or encapsulated fuel particles immersed in a molten salt. This chapter focuses primarily on fluoride salts, but also on chloride and fluoroborate salts based on the preponderance of interest that these salts have received for nuclear energy systems. These molten salts can be quite corrosive at high temperatures with corrosion being driven by thermodynamics, impurity effects, and activity and temperature gradients. Understanding and mitigating materials corrosion in these molten salt environments by appropriate materials selection and salt chemistry control are necessary for their effective implementation in nuclear energy systems.