2018 | AFC ACCOMPLISHMENTS 131 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: The technical goals of this research is to explore the effectiveness of adding minor additives to a metallic fuel to bind fission product lanthanides, with the end goal of preventing or decreasing FCCI.To this end, both tin and palladium were investigated during FY18.The publications listed below detail the work performed to accomplish this goal. The microstructures of U-10Zr-4.3Sn and U-10Zr-4.3Sn-4.7Ln are reported, as well as the diffusion couple results between U-10Zr-4.3Sn and lanthanides. In this diffusion couple test, the lanthanides aggressively attacked the Sn-Zr compounds in U-10Zr-4.3Sn, forming Sn-lanthanide compounds and releasing Zr back into the fuel matrix. In addition to using tin as a stand-alone additive, there was some experimental data suggesting tin and antimony may react differently towards the different lanthanides. Cerium and neodymium are not the same chemically, and do not always react the same, thus additives that target a specific lanthanide may be beneficial.To explore this, the microstructure of U-10Zr-2Sn-2Sb and U-10Zr-2Sn-2Sb-4Ln were analyzed. Diffusion couples between these alloys and either Fe or the lanthanides are underway. It was not possible to determine from the microstructures alone if there is any difference in reactivity between tin, antimony, and specific lanthanides.The diffusion couples should provide the needed information. To explore tin as an additive in a transmutation fuel, U-20Pu-10Zr-4Sn and U-20Pu-10Zr-4Sn-4.3Ln have been fabricated.The as-cast microstructure has been analyzed, and annealing the samples is underway. The annealed microstructures of U-12Zr-4Pd and U-12Zr-4Pd-5Ln were investigated, as well as the as-cast structures for U-20Pu-10Zr-3.86Pd and U-20Pu-10Zr-3.86Pd-4.3Ln. Diffusion couples between the two Pu alloys and Fe have been run.The data is being analyzed.The annealed microstructure of the Pu alloys is also being analyzed. Figure 1 shows theTransmission Electron Microscopy (TEM) Energy Dispersive X-Ray Spectroscopy (EDS) map for a precipitate in annealed U-20Pu- 10Zr-3.86Pd-4.3Ln.With Pu in the alloy, the only Ln-Pd compound is the 1:1 LnPd.The Ln7Pd3 compound, observed in U-12Zr-4Pd-5Ln, does not form.The result of this is too much lanthanides not being bound by Pd. Free lanthanides are present in the precipitates.A manuscript is in progress for both the annealed structures and the diffusion couples. Fuel-cladding chemical interaction due to fission product lanthanides can be prevented using additives to react with the lanthanides, thus extending the lifetime and increasing the potential burn-up of a metallic fuel.