Prediction and Deformation Mechanism Analysis of High Porosity in U–10Mo Monolithic Fuels at High Burnup

High porosity phenomena of U-10Mo fuel foil appear in the U–Mo/Al monolithic fuel plate under deep burnup. In this study, the fuel skeleton creep-based bubble growth model is further improved with the intrusion effect of solid fission products, multiplying the reduction factor in the bubble volume to obtain the bubble pressure. With the locally enhanced irradiation creep of the Mo-depleted region considered, a simulation of the thermo-mechanical coupling behaviors of the monolithic fuel plate L1P7A0 is carried out, based on the commercial finite element (FE) analysis code ABAQUS. A fission-induced creep rate coefficient of 250 × 10−22 mm3/(fission·MPa) is identified for the Mo-depleted region, with the predictions of porosity and the thickness deformation of U–Mo fuel foil agreeing well with the experimental data. The research results indicate that: (1) the locally enhanced fuel skeleton creep ability is responsible for the higher porosities near the U–Mo/Zr interface; (2) the entrance of solid fission products into the fission bubbles at high burnup is the dominant factor in inducing high porosity in the regions of the most heavily irradiated fuel foil, especially near the fuel foil edge bearing the elevated external hydrostatic pressures; (3) with the intrusion effect of solid fission products considered, the prediction of the porosity increases from ~15% to ~35% near the fuel foil edge; (4) the intrusion of solid fission products leads to extra differences between the bubble pressure and the external pressure, and simultaneously results in the strengthened fuel skeleton creep deformation contributions to the bubble growth.