Effect of palladium on the microstructure and grain boundary complexions in SiC

TL;DR

This study investigates how palladium diffusion alters the microstructure and grain boundary properties of SiC, potentially facilitating faster diffusion of fission products in nuclear fuel particles.

Contribution

It reveals that palladium induces grain boundary complexion transitions and microstructural changes in SiC, a novel insight into fission product diffusion mechanisms.

Findings

Palladium increases high angle grain boundaries from 47% to 59%.

Palladium leaves excess carbon at grain boundaries.

Palladium induces grain boundary complexion transition.

Abstract

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.