Melt refining experiments in which irradiated uranium or synthetic EBR- II alloys were melted in oxide crucibles showed that removal of zirconium as an oxide does not occur at temperatares up to 1400 ts C. Removal of zirconium by carbon scavenging of the melt was approximately 50% in 5-hr melts at 1400 ts C; the mechanism and products of reactions which led to this separation are discussed. Zirconium contamination of uranium- cerium alloys melted in limestabilized zirconia crucibles was negligible. (auth)