Diffusion Barrier Coatings for Liquid Metal Corrosion Resistance in Next-Generation Nuclear Reactors

Abstract

The goal of this study is to characterize the chemical and physical interactions that occur between a ceramic diffusion barrier coating applied onto nuclear reactor cladding, liquid metal coolants, and metallic fuel used in Sodium-Cooled Fast Reactors (SFRs) and Lead-Cooled Fast Reactors (LFRs). In SFRs and LFRs, damage to cladding and structural materials from the liquid metal coolant poses large issues for reactor safety and stability. As an approach to this issue, two compositions of a ZrO2 based coating have been proposed to protect the structural materials from interacting with the liquid metal: ZrO2 with Sn metal and ZrO2 with Sb metal. The ZrO2 is meant to provide a physical barrier, preventing motion of species into and out of the cladding material while the Sn and Sb metals are added for a separate function of trapping lanthanide fission products released from the fuel for mitigating fuel-cladding chemical interactions (FCCI). Three series of experiments were done to test the integrity of these coatings in reactor conditions (500°C for SFRs and 600°C for LFRs) including standard immersion corrosion tests in liquid metal, 'liquid-like' diffusion couple tests to model transport through a liquid metal medium, as well as solid-state diffusion couple tests. Experimentation and characterization have confirmed the stability and effectiveness of these coatings in liquid lead but not in liquid sodium due to sodium's high reactivity with oxygen. Further investigations showed that new phases formed when liquid lead interacted with Sn in the coating, inferring the viability of Sb as an additive instead of Sn. Sb as an additive also supported the formation of a more compact coating, which shows to be desirable for mitigating the diffusion of liquid metals.