Skeleton-creep based bubble growth model and multi-scale mechanical constitutive model for U-10Mo fuels under irradiation

Abstract

The macroscale irradiation swelling deformations of nuclear fuels induced by the solid and gas fission products are one of the most concerned problems in nuclear reactor core design. Based on continuum mechanics, an innovative macroscale volume growth strain model is proposed for U-10Mo fuels, with the coupling contributions of irradiation creep, fission solid swelling and thermal expansion of fuel skeleton. Correspondingly, new three-dimensional mechanical constitutive models and stress update algorithms are also developed for the multi-scale irradiation-deformation and stress analysis. Good agreements of the predictions with diverse experimental data validate the effectiveness of newly developed models. It is obtained that the growth of fission gas bubbles is dominated by the creep deformations of the surrounding fuel skeleton, depending on the external hydrostatic pressure and the internal bubble pressure related to the intra-granular fission gas atom diffusion; the influences of temperature, external hydrostatic pressure and fuel-skeleton creep rate coefficient are found to become prominent at higher burnup levels, dominantly induced by the coupling of fuel-skeleton creep and local porosity. This study provides a new insight into the mechanism of bubble growth in the solid skeleton, revealing the coupling of irradiation swelling with fuel-skeleton creep.