Fission-enhanced self-diffusion of uranium in UO 2 and UC

Abstract

In-pile self-diffusion measurements in stoichiometric UO 2 sinters and single crystals and in arc-cast stoichiometric UC have been performed using the thin layer condition and 233U as tracer. The nominal irradiation temperature was 900°C. The resulting diffusion coefficients D∗ of 1.5 × 10 −16 cm 2 · sec −1 for UO 2 and 2.2 × 10 −17 cm 2 · sec −1 for UC for a fission rate S of 1 × 10 13f/cm 3 · sec represent radiation enhanced diffusion and are higher by factors of 10 3 to 10 4 than (extrapolated) coefficients of thermal diffusion. The data are of immediate relevance for understanding and predicting such important quantities as in-pile sintering and densification, diffusion controlled creep and fission gas behavior in the outer zones of the fuel. They are at the upper limit of expected values.