Recommendations for calculating the rate of irradiation-induced creep of oxide fuel when analyzing fuel-element serviceability

Recommendations for calculating the characteristics of irradiation-induced creep of mixed uranium-plutonium oxide fuel and uranium dioxide for programs analyzing fuel-element serviceability are developed on the basis a physical model of deformation. The deformation processes in the model include the mechanism of modular interaction of radiation defects with dislocations and radiation diffusion. It is shown on the basis of an analysis of the dynamics of radiation point defects that the rate of irradiation-induced creep is determined by the sum of thermal and athermal components. Thermal creep makes a large contribution at temperatures above one-half the melting temperature. The model takes account of the effect of temperature, stress, fission density, and fuel burnup and density on the rate of irradiation-induced creep. The use of physical models to obtain computational relations made it possible to improve by approximately a factor of 10 the agreement between calculations and experimental data as compared with empirical relations previously used to describe the characteristics of creep.