Distribution of fission products palladium, silver, cerium and cesium in the un-corroded areas of the locally corroded SiC layer of a neutron irradiated TRISO fuel particle

Detailed electron microscopy studies were performed to investigate distribution and composition of fission products in the SiC layer of a tristructural-isotropic-coated particle exhibiting localized corrosion. Previous studies on this particle indicated that pure carbon areas in the SiC layer, resulting from localized corrosion of SiC by Pd, provide pathways for Ag, Cd, and Cs migration. This study reveals the presence of Ag- and/or Cd-containing precipitates in un-corroded SiC areas. Ag and Cd may exist by themselves or coexist with Pd. Ag and Cd mainly transport along SiC grain boundaries. An Ag-Pd-Cd precipitate was identified at a stacking fault inside a SiC grain, suggesting that intragranular transport of Ag and Cd is possible. Ce is present with Pd or Pd-U in some precipitates. U and Ce frequently coexist, whereas Ag and Cd usually do not coexist with U or Ce. No Cs was detected in any precipitates in the areas examined.