2017 | AFC ACCOMPLISHMENTS 140 Figure 1. a) SEM backscatter image of U-10Zr-4.3Sn-4.7Ln; b) SEM backscatter image of U-10Zr-4.3Sn/ Ln diffusion couple interface. 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 and palladium 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. Project Description: The technical objectives of this research are to investigate additives to metallic fuels to improve the 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 Department of Energy (DOE) meet its objectives of a safe, reliable, and economic reactor by significantly improving fuel performance. By preventing FCCI due to the fission product lanthanides, cladding ruptures will be prevented, improving fuel safety and reliability, and higher fuel burn-up will be possible, thus improving reactor economics by decreasing the amount of fuel required, and decreasing the amount of nuclear waste generated. Accomplishments: In FY17, investigations began using tin as an additive to control FCCI. Alloys analyzed include U-10Zr-4.3Sn- 4.7Ln, as well as alloys with a high or low lanthanide loading, U-10Zr- 2Sn-4.3Ln and U-10Zr-4.3Sn-2Ln. Figure 1a shows the scanning electron microscope (SEM) image of U-10Zr- 4.3Sn-4.7Ln. EDS analysis indicates the round precipitates are Ln5Sn3 .The long, dark precipitates are Zr5Sn3, while the matrix is comprised of alpha-U (light areas) and delta phase (UZr2, dark grey areas).To be considered a Alloy Optimization Casting and Characterization Studies Principal Investigator: Michael T. Benson Collaborators: James King, Robert Mariani