Creep fracture processes in uranium dioxide

Abstract

Creep fracture processes have been studied in UO 2. At high rates of strain fracture occurs by the propagation of the triple point cracks which extend large distances along grain boundaries. At lower rates of strain the fracture mode involves the growth of rounded cavities on boundaries parallel to the compressive stress axis. The growth of these cavities is attributed to a vacancy condensation mechanism driven by internally generated tensile components of stress. The magnitude of this tensile stress is calculated and the conditions for growth are estimated. It is shown that non-stoichiometric and large grained material is more susceptible to creep damage. This increased susceptibility is attributed to the increased magnitude in grain boundary sliding offsets in the large grained material and to increased ease of sliding in the non-stoichiometric material.