Experimental and Simulation Insight on the Transport of Silver Fission Product in SiC

Understanding of the fission product transport in TRISO fuel particles is fundamental to improving the safety and performance of high temperature gas cooled reactors. Previous experiments showing silver release from TRISO fuel have focused on release measurements and not direct observation of the fission product transport. The possible diffusion of Ag via a grain boundary diffusion mechanism is being examined. By characterizing the SiC grain boundary structure according the coincidence site lattice scheme and detecting diffusion along specific grain boundaries, insight into the relationship between SiC microstructure and Ag release may be obtained. In addition computer modeling is being used to investigate the diffusion of silver through SiC. We employ a multi-scale approach based on ab initio techniques, molecular dynamics, and continuum rate equations in order to establish relationships between complex microstructures and diffusion rates. Initial work has begun on transport through bulk SiC and on building realistic models of grain boundaries in SiC.