  One of the main challenges in the study of TRISO (Tristructural Isotropic)
coated fuel particles is the understanding of the diffusion of fission products
through SiC. Among the elements produced inside the uranium kernel, it has been
suggested that Pd might enhance the diffusion of other fission products. In
this work we have studied the interaction between Pd and SiC. We have observed
that as Pd diffuses it can change the chemical composition and microstructure
of SiC. Electron Backscattered Diffraction (EBSD) analysis showed that Pd
increased the amount of high angle grain boundaries from 47 to 59%.
Furthermore, we have observed that as Pd diffused, it changed the composition
of SiC by leaving a trail of excess carbon at the grain boundary. This change
in localized chemical composition and microstructure suggests a grain boundary
complexion transition induced by Pd and a new way in which Pd can lead to
faster diffusion routes for other fission products.
