Nuclear Science User Facilities 86 Microstructure Characterization of High-energy Xe Ion Irradiated U-Mo BeiYe – Argonne National Laboratory – In this project, U-Mo/Al dispersion fuel samples irradiated with high energy heavy ions were character- ized withTEM to reveal ion modified microstructure in U-Mo. Qualitative and quantitative assessments of the microstructural evolution of U-Mo as a function of the ion penetration depth were obtained. Project Description U-Mo/Al dispersion fuels, developed for reducing uranium enrichment in research and test reactor fuels for non-proliferation purpose, underwent drastic microstructural changes during in-pile irradiations, including the excessive growth of (U,Mo)AlX interdiffusion layer and large fission gas filled pores at the interfaces of U-Mo fuel particles and the Al matrix. Figure 1. An overview of the TEM sample prepared from a U-Mo/Al sample irradiated with 84 MeV Xe ions to a dose of 2.9 × 1017 ions/cm2 . The information obtained in this study provides new perspective on microstructural evolution in nuclear fuels under irradiation, for example, irradiation induced recrystallization.