b'Figure 2. SEM and EDS of a cross section of as-cast AFA with UN+UO 2annealed at 750C-1000 hr. No AlN formation is observed, and an alumina-enriched scale formed at the interface with the presence of oxygen from the secondary phase of UO 2in the fuel matrixat 550C for 500 and 1000 hours. Atformed with the presence of oxygen 750C, a secondary phase of AlN alsodue to the secondary phase oxide in formed along the interface intermit- the UN matrix. No chemical interac-tently for the UN or UN+U pellets. Intion and interdiffusion occur upon the inert environment of the diffusionthe interaction of UN with preoxi-couple experiment, the aluminumdized AFAs. AFAs are designed with can readily form nitride at 750C.aluminum diffusing to the surface The formation of AlN is also thermo- during normal operation, and an dynamically possible at 550C, butoxide scale forms in the preoxidized the lower temperature likely limitssamples, preventing possible interac-diffusion of aluminum to the surfacetion and elemental interdiffusion. and diffusion of nitrogen out of theThese results highlight the important UN pellet. In addition, no AlN forma- impacts of the protective alumina tion was observed in the UN + UO 2 scale, temperature, and secondary (3 wt%) and as-cast AFA when testedphases on the chemical interaction at 750C for 1000 hours, and insteadand interface reaction between UN an aluminum-enriched surface scaleand AFA.150 2023|AFC ACCOMPLISHMENTS'