On the performance of metallic coating barriers in U-Mo/Al fuels: A quantitative evaluation of Al/X/U-Mo trilayer structures (X = Mo, Zr, or W) under heavy ion irradiation

This study evaluates the effectiveness of molybdenum (Mo), zirconium (Zr), and tungsten (W) coatings as diffusion barriers in U-Mo/Al fuel systems, aiming to suppress interdiffusion between U-Mo and Al, a process that significantly degrades fuel performance. Well-defined Al/X/U-Mo trilayer structures (X = Mo, Zr, or W) with coating thicknesses ranging from 50 nm to 5 µm were subjected to heavy ion irradiation with iodine or xenon ions up to 7 × 10 17 ions/cm 2 , simulating fission product damage under varied irradiation conditions. Cross-sectional scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses revealed distinct performance trends: Mo coatings underwent rapid consumption and formed Al-Mo intermixing layers that promoted continued U-Mo-Al interdiffusion, indicating poor long-term stability. Zr coatings exhibited thickness-dependent behavior, with thin layers fully consumed while thicker coatings provided notable resistance. W coatings with thicknesses ≥ 1 µm showed the highest stability, effectively suppressing interdiffusion under the tested conditions, consistent with the less thermodynamically favorable formation of Al-W compounds. These findings provide quantitative guidance for selecting robust diffusion barriers in advanced U-Mo/Al fuel architectures and help explain mechanisms observed in in-pile irradiation experiments.