Interdiffusion and chemical diffusion in the UO2 — (U,Pu)O2 system

Abstract The chemical or interdiffusion of metal atoms (U and Pu) in the system UO 2 ± x -(U,Pu)O 2 ± x was studied as function of oxygen potential, ΔḠ(O 2 ) or O/M-ratio. High-resolution α-spectroscopy and electron microprobe analysis were used to measure diffusion profiles of couples of UO 2 /(U,Pu)O 2 of different O/M-ratio. For most experiments, a mixed oxide of (U 0.83 Pu 0.17 )O 2 ± x was used. O/M-ratios were varied by using controlled mixtures of CO/CO 2 . The Matano-Boltzmann-type analysis was employed to evaluate the interdiffusion curves. A pronounced dependence of the interdiffusion coefficients, D, on O/M-ratio was observed, with D greatly increasing with increasing O/M-ratio. D was also shown to increase with Pu-content in the range of about 4 to 17% Pu. Fast penetration of major quantities of Pu along grain boundaries into UO 2 was observed at high temperatures.