Application of high-temperature ceramic plasma-spray coatings for a reusable melting crucible

Metallic fuels, such as the U-Zr alloy system for sodium-cooled fast reactor (SFR), are melted in a Y2O3 slurry-spray-coated graphite crucible in order to prevent melt/material interactions. Reactive and porous coatings such as the Y2O3 slurry-spray-coating are a source of melt contamination and fuel loss, respectively. Therefore, a dense plasma-spray coating of non-reactive materials is desirable for a reusable melting crucible. In this study, ceramic materials such as Y2O3 and 8 mol% Y2O3-st. ZrO2, are selected as candidate protective coating materials for reusable crucibles for melting metallic fuel slugs. Studies are conducted to characterize the thermal cycling performance of the coatings, and the interactions between the U-10wt% Zr fuel and the coating layer on the substrates. The thermal cycling tests of the ceramic plasma-spray coatings exhibit good thermal cycling characteristics with few interconnected cracks. The Y2O3 plasma-spray coating does not form a significant reaction layer between the melt and the coating layer due to the thermodynamic stability of Y2O3. Hence, the Y2O3 plasma-spray coating exhibits the most promising performance among the ceramic coatings investigated, for use in reusable melting crucibles.