Synthesis and microstructural properties of porous UO₂/B₂O₃ eutectic ceramic composites as mock nuclear fuel debris

In this work, UO₂/B₂O₃ eutectic ceramic composites were prepared by spark plasma sintering, and the effect of the cooling rate on the microstructural properties was investigated. Mixtures of UO₂ and B₂O₃ powders were prepared with the eutectic composition. The mixtures were placed in boron nitride crucibles and melted at 2073 K for 10 min in an argon flow. The obtained ingots were crushed into fine powders, then sintered again with and without the application of pressure for 10 min at 1647 K and 2073 K, respectively. Four kinds of UO₂/B₂O₃ eutectic composite samples with different cooling rates were prepared. The ingot and sintered samples characterized using X-ray diffraction showed that UO₂ was the predominant crystalline phase. The microstructures of the ingots and sintered samples were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The SEM observations revealed that the UO₂/B₂O₃ composite had a eutectic structure with nanoscale lamellar. The EDS analyses revealed that B and O rich phases existed around the pores in the samples. It was also found that the size of the pores increased and the density of the material decreased with decreasing cooling rates which would make influence on the properties of debris. (author)