Surface-Diffusion Studies on UO(2) and MgO

An optical interferometric technique has been used to study the growth of grain boundary grooves and the decay of surface scratches on UO(2) and MgO at temperatures in the range 1100 to 1700 degrees C. The results were interpreted using equations derived by W. W. Mullins and it was found that surface-diffusion was the predominant material transport process for both oxides under the experimental conditions used. Surface-diffusion coefficients and activation energies were calculated, and gave the following equations for the variation of the mass transfer surface-diffusion coefficient D(s) with temperature. UO(2.005), D(s) = 1.3 x 10(8) exp(-110000 +/- 15000)/RT [1200 to 1400 degrees C] MgO, D(s) = 8 x 10(4) exp(-88500 +/- 15000)/RT [1200 to 1500 degrees C] It was found that for UO(2) the rate of grooving increased markedly as the oxygen content of the oxide increased.