Interaction phenomena between ceramic coatings and liquid uranium alloys

Abstract

Owing to the high chemical reactivity of molten uranium alloys, the use of traditional graphite crucibles for casting fuel slugs for a sodium-cooled fast reactor (SFR) is problematic. Moreover, rare earth (RE) elements retained in the fuel slugs for an SFR, which are extracted from the spent fuel by pyro-processing, are more reactive than uranium melt. Therefore, in this study, Y₂O₃ single-layer coatings with thicknesses of approximately 50, 70, and 120 μm and double-layer coatings of TaC/Y₂O₃ and Y₂O₃/TaC were plasma-sprayed onto niobium substrates and tested for thermal shock resistance and compatibility against U–10 wt% Zr and U–10 wt% Zr–5 wt% RE melt. The Y₂O₃ single-layer coating, regardless of coating thickness, and the TaC/Y₂O₃ double-layer coating showed good contact at the interface between the coating and the niobium substrate, with no deterioration after the thermal cycling test. In the interaction studies, the single- and double-layer coatings showed good compatibility with the U–Zr melt. However, the Y₂O₃ coatings with thicknesses of approximately 50 and 70 μm showed severe penetration of the U–Zr–RE melt and reacted with the niobium substrate. The single-layer Y₂O₃ coating with a thickness of 120 μm and the double-layer TaC/Y₂O₃ coating exhibited the most promising performance among the candidate coatings.