The influence of stoichiometry on compression creep of polycrystalline UO 2+ x

Abstract

Compressive creep tests have been performed on polycrystalline hyperstoichiometric uranium dioxide, as a function of temperature, stress and deviation from stoichiometry. Under low stresses measured steady-state creep rates for UO 2+ x increase linearly with applied stress, σ, and with oxygen excess, x. Creep rates for UO 2+ x tested at high stresses follow a power-law stress dependence of the form ε ̇ ∝ σ n where 4< n<7, and increase with x m where 1.75< m< 2. The transition stress, σ t, between linear and power-law stress dependence behavior decreases with increasing O U ratio. For polycrystals tested at high stresses, the creep activation energy, Q c , decreases with increasing x in the same manner as found for uranium dioxide single crystals. Creep activation energies also decrease with increasing x in the linear stress-dependence region, but values for Q c are lower at a given x than are values obtained in the power-law stress region. It is suggested that different diffusion processes control the observed creep behavior in the two different stress regimes.