Characterization of U-10Zr-2Sn-2Sb and U-10Zr-2Sn-2Sb-4Ln to assess Sn+Sb as a mixed additive system to bind lanthanides

Tin and antimony are being investigated as potential additives to metallic fuel to control fuel-cladding chemical interaction (FCCI). A primary cause of FCCI is lanthanide fission products moving to the fuel periphery and interacting with the cladding. This interaction can lead to wastage of the cladding and, given enough time or burn-up, eventually to a cladding breach. The current study involves a microstructural characterization of as-cast and annealed U-10Zr-2Sn-2Sb and U-10Zr-2Sn-2Sb-4Ln, where Ln = 53Nd-25Ce-16Pr-6La, all in wt %, as alloys which could prevent FCCI. Scanning electron microscopy (SEM) analysis and X-ray powder diffraction indicates the additive-Zr compound in U-10Zr-2Sn-2Sb is Zr5(Sn,Sb)3, while the additive-Ln compound being formed in U-10Zr-2Sn-2Sb-4Ln is Ln5(Sn,Sb)4, with significantly more Sb than Sn (37 at. % versus 6 at. %, respectively). The bulk of the Sn, with a small amount of Sb, remained as Zr5(Sn,Sb)3 precipitates. The potential benefits of a mixed additive system, along with relative stabilities of the intermetallic compounds, are discussed.