Radiation enhanced diffusion in UO2 and (U,Pu)O2

Abstract

The radiation enhanced diffusion (coefficient D*) of U-233 and Pu-238 in UO₂ and (U, Pu)O₂ with 2.5 and 15% Pu was measured during fission in a nuclear reactor. Normal diffusion sandwiches with a thin tracer layer were used. A radio-frequency furnace allowed the temperatures to be varied between 130 and 1400°. Neutron fluxes (7 × 10¹² to 1.2 × 10¹⁴ n cm^?2 s^?1) and irradiation times (56 to 334 h) were also varied to cover ranges of fission rates Fdot] between 7× 10¹¹ and 6.4 × 10¹³ f cm^?3 s^?1 and of doses F between 4.2 × 10¹⁷ and 3.1 × 10¹⁹ f cm³. Below ～1000°, D* was completely athermal and increased linearly with Fdot]. It was described by D* = AFdot] with A = 1.2× 10^?29cm⁵. A possible temperature dependence was indicated between ～1000and 1200°. The results are explained in terms of thermal and pressure effects of fission spikes and are related with other studies of radiation damage as well as with technologically interesting processes occurring in UO₂ during irradiation.