Corrosion of Structural Materials in Liquid Lead Alloys for Nuclear Applications

The corrosion behavior of structural materials in liquid lead alloys like Pb-17Li as a liquid tritium breeder for future fusion reactors and Pb-55Bi (lead-bismuth eutectic [LBE]) as an envisaged spallation target and/or coolant for accelerator-driven systems (ADS) and lead-cooled Gen IV reactors is a key issue in the road map for developing new energy systems within the next decades. Ferritic-martensitic steels of the 8 wt% to 10 wt% Cr type are considered as structural materials for use in liquid Pb-17Li at temperatures up to 550°C. Due to the specific physical chemistry of Pb-17Li, dissolution corrosion is the major corrosion mechanism of iron-based alloys. No oxide formation on steel surfaces can occur because of the very low oxygen potential. Therefore, coatings could/must be applied to minimize corrosion effects at medium (500°C) and higher operational temperatures (650°C) of advanced fusion blanket concepts. Ferritic-martensitic and austenitic CrNi steels are considered potential structural materials for ADS and Gen IV reactor applications. Nevertheless, the high nickel solubility in LBE limits the use of unprotected austenitic steels to temperatures of about 550°C. Because of the much higher oxygen potential in LBE, a totally different strategy of minimizing corrosion must be adopted. By using active oxygen control, a desired oxygen activity will be adjusted in the liquid metal via gas phase equilibrium, which enables the controlled formation of oxide layers on the steel surfaces. These in situ-formed oxides can act as corrosion barriers and make use of high-nickel alloys possible, even at temperatures around 600°C.