Tristructural-isotropic (TRISO)-coated fuel particles are used in high-temperature gas-cooled nuclear reactors. Although the polycrystalline 3C–SiC layer acts as the main barrier to fission product release, post-irradiation examinations have shown that certain metallic fission products are found on the outside of the TRISO coated particle, with no observable evidence of micro-cracks or mechanical failure. In this study, an atomic resolution transmission electron microscopy investigation of a SiC layer from a neutron irradiated (19.38% fissions per initial metal atom average burnup; 1072 °C time-averaged temperature) TRISO-coated particle from the first fuel irradiation experiment as part of the US DOE Advanced Gas Reactor Fuel Qualification and Development (AGR) Program, was conducted. The fission product Pd was found to be present at dislocation cores associated with twins, stacking faults, and their intersections as atomic scale silicide inclusions. EELS elemental quantification of the silicide region showed a reduction of C and increase of Si in the Pd containing inclusion. Pd was also observed as distributed along grain boundaries down to the atomic scale. The local corrosion and dissociation of C from Pd containing grain boundary agglomerations was observed at the atomic level. Elemental quantification of atomically dispersed Pd grain boundary regions using EELS spectrum imaging similarly showed a measurable decrease in C concentration at Pd regions and an increase in Si concentration.

涂有三向同性（TRISO）的燃料颗粒用于高温气冷核反应堆。尽管多晶3C–SiC层是裂变产物释放的主要障碍，但辐照后的检查表明，在TRISO涂层颗粒的外部发现了某些金属裂变产物，没有可观察到的微裂纹或机械故障的证据。 。在这项研究中，中子辐射的SiC层的原子分辨率透射电子显微镜研究（每个初始金属原子平均燃耗为19.38％的裂变； 1072°C时平均温度）来自第一次燃料辐照实验的TRISO涂层颗粒作为一部分进行了美国能源部高级气体反应堆燃料合格与开发（AGR）计划的审核。发现裂变产物Pd以原子级硅化物包裹体的形式存在于与孪晶，堆垛层错及其相交处的位错核中。EELS对硅化物区域的元素定量显示，含Pd的夹杂物中C的减少和Si的增加。还观察到Pd沿晶界分布到原子级。在原子水平上观察到了C从含Pd的晶界团聚体中的局部腐蚀和离解。使用EELS光谱成像对原子分散的Pd晶界区域进行元素定量分析，同样显示出Pd区域的C浓度可测量的下降和Si浓度的增加。EELS对硅化物区域的元素定量显示，含Pd的夹杂物中C的减少和Si的增加。还观察到Pd沿晶界分布到原子尺度。在原子水平上观察到了C从含Pd的晶界团聚体中的局部腐蚀和离解。使用EELS光谱成像对原子分散的Pd晶界区域进行元素定量分析，同样显示出Pd区域的C浓度可测量的下降和Si浓度的增加。EELS对硅化物区域的元素定量显示，含Pd的夹杂物中C的减少和Si的增加。还观察到Pd沿晶界分布到原子级。在原子水平上观察到了C从含Pd的晶界团聚体中的局部腐蚀和离解。使用EELS光谱成像对原子分散的Pd晶界区域进行元素定量分析，同样显示出Pd区域的C浓度可测量的下降和Si浓度的增加。