It was noted that undesired release of Cs through a silicon carbide coating of nuclear fuel was a concern in the design of very high temperature reactors. However, the mechanisms of Cs transport were still unclear. Density functional theory was used here to study the diffusion of Cs in crystalline bulk SiC. The Cs point defects and Cs vacancy clusters were investigated for stability and structure. The most stable state for the Cs impurity in SiC, under n-type doping conditions, was found to be a negatively charged Cs atom substituting for a C atom and bound to two Si vacancies (CsC-2VSi3-). Bulk diffusion coefficients were estimated for several Cs impurity states. The (CsC-2VSi3-) defect structure was found to have the lowest overall activation energy for diffusion, with a value of approximately 5.14eV. This activation energy agreed well with diffusion activation energies estimated for Cs in SiC based on high temperature integral release experiments.

Cs Diffusion in Cubic Silicon Carbide. D.Shrader, I.Szlufarska, D.Morgan: Journal of Nuclear Materials, 2012, 421[1-3], 89-96