2018 | AFC ACCOMPLISHMENTS 130 Figure 1. TEM EDS maps for a precipitate in U-20Pu-10Zr- 3.86Pd-4.3Ln Fuel-cladding chemical interaction (FCCI) occurs when the nuclear fuel or fission products react with the cladding material.A major cause of FCCI in U-Zr and U-Pu-Zr fuels during irradiation is fission product lanthanides (Ln), which migrate to the fuel periphery, coming in contact with the cladding.The result of this interaction is degradation of the cladding, and will eventually lead to rupture of the fuel assembly. Tin, palladium, and to a lesser extent antimony, are being investigated as minor component additives to control FCCI in metallic fuels specifically due to lanthanides.The role of the additive is to prevent FCCI by forming very stable intermetallic compounds with the lanthanides, thus preventing interaction with the cladding. Studies are underway to characterize the effects of these additives in a metallic fuel. Alloy Optimization Casting and Characterization Studies Principal Investigator: Michael T. Benson Collaborators: James A. King Project Description: The technical objectives of this research are to investigate additives to metallic fuels for improved FCCI performance. Previous work on palladium has shown promising results for controlling FCCI.The current work is a continuation of that work with palladium, as well as expanding the investigation to include tin.The objective of this work is to characterize the microstructure of the metallic fuels with these additives, and to evaluate performance in out-of-pile tests.This work was carried out using U-Zr based fuels as well as U-Pu-Zr based fuels. An additive that effectively controls FCCI will help the DOE meet its objectives of a safe, reliable, and economic reactor by significantly improving fuel performance. By preventing FCCI due to the fission