Potential source of carbon contamination in U-Zr melt processed in Y2O3-plasma-spray-coated graphite

This study investigated carbon contamination in U-10wt.%Zr metallic fuel in the casting process based on the interaction between the U-Zr alloy melt and the Y₂O₃-plasma-spray-coated graphite. During the injection casting of U-10wt.%Zr, a ZrC reaction layer was found to form at the interface between the U-Zr melt and the Y₂O₃-plasma-coated graphite crucible. ZrC inclusions were also found in the matrix of the melt residue. This C contamination, evidenced by the formation of ZrC, is attributed to the migration of C through the Y₂O₃ coating from the graphite crucible. The results of TGA experiments using a Y₂O₃-plasma-coated graphite sample suggest that CO is produced by a reaction between Y₂O₃ and graphite at temperatures above 1773 K, which then migrates through defects in the coating to react with Zr in the U-Zr melt.