Identification of Ag-Rich Phase in TRISO Fuels by Using Atom Probe Tomography

As a fission product in the SiC layer of tristructural-isotropic (TRISO) coated particle after neutron irradiation, Ag-rich phase was discovered recently by using transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy techniques. However, quantitative analysis is limited in analyzing the nanosized Ag-rich phase due to the inherent two-dimensional information obtained from TEM technique. Atom probe tomography (APT) is a unique technique that provides both atom position and chemical identity in real three-dimensional space at near atomic level, which make it possible to do quantitative analysis accurately. However, SiC is an extremely difficult material for the APT technique due to the large difference in evaporation field between C and Si. In addition, irradiated sample is more challenging due to high number density of defects. In this study, lessons were learned to overcome the challenges and an Ag-rich phase was detected. Details will be discussed.