ON URANIUM SELF-DIFFUSION IN UO2 AND UO2+X

Self-diffusion coefficients of uranium in sinters and single crystals of uranium oxide with varying oxygen content were measured between 1200 and 1600 °C using the method of α-energy degradation. Carefully determined D-rmvalues for UO2 heated in hydrogen were found to be very low compared to most previously published results, provided the annealing time was long ( > 100 h). The most probable reasons for this discrepancy are either the effect of impurities with valences < 4 (extrinsic diffusion) or else reduction of the UO2 to substoichiometry. For UO2+x, higher uranium diffusion coefficients were observed, in accordance with theory and previous results. At 1500 °C, the dependence of D on x in UO2+x could be described by log D = -10.85 + 1.5 log x. A value of 4.8 ± 0.3 eV (110 ± 7 kcal/mole) is suggested as the most probable value for the activation enthalpy of uranium diffusion in UO2. © 1969.