This work presents a comparison between the microstructural evolution of three annular fast-reactor mixed-oxide (MOX) fuel pellets irradiated to varying burnups at the Fast Flux Test Facility (FFTF). Fuel pellets irradiated to 3.4%, 13.7%, and 21.3% fissions per initial metal atom (FIMA) were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The cross-section of the low burnup pellet displayed minor structural changes, but the central annulus of the pellets at 13.7% and 21.3% FIMA shrank from their starting size. The high burnup fuel pellet featured streaking and porosity migration associated with columnar grain growth. The radial fission product distribution in each of the pellets had a higher number density of metallic particles >5 μm in diameter near the fuel centerline. Solid fission products in the fuel-cladding gap were observed in the low and intermediate burnup pellets. The low burnup sample showed minor accumulation of Ba in the gap, while the volatile Cs was primarily observed at the pellet surface. The intermediate burnup pellet displayed a porous mixture of fission products, consistent with the joint-oxide gain (JOG) that has been previously observed in fast-reactor MOX fuel pellets.

这项工作提出了在快速通量测试设施（FFTF）下辐照到不同燃耗的三个环形快速反应器混合氧化物（MOX）燃料颗粒的微观结构演变之间的比较。使用扫描电子显微镜（SEM）和能量色散X射线光谱（EDS）技术检查了每个初始金属原子（FIMA）分别照射到3.4％，13.7％和21.3％裂变的燃料芯块。低燃耗粒料的横截面显示出较小的结构变化，但是粒料的中心环在FIMA的13.7％和21.3％处比其起始尺寸缩小。高燃耗燃料颗粒具有与柱状晶粒生长相关的条纹和孔隙迁移。每个颗粒中的径向裂变产物分布在燃料中心线附近具有直径> 5μm的更高数量的金属颗粒。在中低燃耗球团中观察到燃料包壳间隙中的固体裂变产物。低燃耗样品显示间隙中Ba积累较少，而挥发性Cs主要在颗粒表面观察到。中间燃尽颗粒显示出裂变产物的多孔混合物，这与先前在快速反应器MOX燃料颗粒中观察到的联合氧化物增益（JOG）一致。