Self-Diffusion Processes in Nuclear Carbonitrides UC_xN_{1 − x} and (U, Pu)C_0.8N_0.2

The self-diffusion of ¹⁴C and ²³³U in four different uranium carbonitrides, UC_xN_1−x with x = 0.67, 0.26, 0.24, and 0.18, and the diffusion of ²³⁸Pu in two sets of (U,Pu)C_0.8N_0.2 were measured. Replacing carbon by nitrogen decreased self-diffusion rates in both metal and nonmetal lattices. The decrease was not linear with x; rather, a change in mechanism or bonding at around x ≈ 0.5 was indicated. The data are of importance for both fabrication and reactor operation of carbonitrides.