On the degradation of Young's modulus of irradiated U-10Mo

Theoretical analysis of the four-point bending experimental results from the reference has demonstrated that the effective Young's modulus of heavily-irradiated U-10Mo fuel undergoes a significant reduction. However, the underlying mechanisms need to be fully elucidated. In this study, the irradiation-induced thermo-mechanical coupling behaviors of monolithic fuel plates are first numerically investigated by employing the fuel skeleton creep-based volumetric growth strain model and the porosity-related macroscale creep rate model for the contained U-10Mo fuel foils. The predicted average thicknesses for the bending specimens from several fuel plates align well with the experimental measurements, validating the adopted models, algorithms and the obtained macroscale porosity values for irradiated U-10Mo fuel. The values of effective Young's modulus of U-10Mo fuel after different levels of irradiation are identified through the subsequent direct simulations of the four-point bending tests, with the numerically acquired macroscale mechanical responses of irradiated U-10Mo specimens matching the experimental data. After eliminating the effects of fuel porosity, it is found that the values of Young's modulus of dense U-10Mo fuel skeleton decrease with increasing fission density or macroscale porosity, thereby becoming a primary contributor to the degradation of the effective Young's modulus of irradiated U-10Mo fuel. Furthermore, mathematical models for the Young's modulus of irradiated U-10Mo fuel skeleton at room temperature are developed as functions of fission density and macroscale porosity, respectively. The predicted results indicate that the von Mises stress will significantly decrease and the equivalent creep strains might have a distinct increase, when the degradation of Young's modulus of fuel skeleton is incorporated. This work provides a foundation for the high-precise modeling of the irradiation-induced thermo-mechanical behaviors of the U-10Mo-based fuel elements or assemblies.