Effect of Oxygen Potential on the Thermal Creep of Niobia Doped UO ₂

Abstract

Compressive and tensile creep were measured on UO 2 doped with 0.4 wt % niobia at controlled oxygen potentials. Kinetic results were almost identical, irrespective of the nature of the applied stress, but differences in after‐test microstructures were observed. Formation of “plastic” UO 2 with increases in strain rate of more than two orders of magnitude were recorded when oxygen potential changed from −560 to −410 kJ/mol; this was associated, primarily, with the formation of the Nb 4+ ion. Over the same range of oxygen potential, creep activation energy decreased linearly from −425 to −225 kJ/ mol. In contrast, strain rate and activation energy for undoped UO 2 remain almost constant under these conditions.