On the Young's Modulus Degradation of Irradiated U-10mo Fuels

Abstract

Theoretical analysis of the four-point bending experimental results in the reference demonstrated that a significant reduction occurred in the effective Young’s modulus of U-10Mo fuels after irradiation to high burnup, with the underlying mechanisms needing to be further revealed. In this study, the irradiation-induced thermo-mechanical coupling behaviors of monolithic fuel plates are numerically investigated firstly, employing the fuel skeleton creep-based volume growth strain model and the porosity-related macroscale creep rate model for the contained U-10Mo fuel foils. The predictions of thickness increments for several fuel plates agree well with the experimental measurements, validating the adopted models, algorithms and the obtained macroscale porosity values for irradiated U-10Mo fuels. The values of effective Young’s modulus of U-10Mo fuels after different levels of irradiation are identified by 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, which is also responsible for the degradation of effective Young’s modulus of irradiated U-10Mo fuels. Besides, a mathematical model for the Young’s modulus of irradiated U-10Mo fuel skeleton at room temperature is developed as a function of fission density. The predicted results indicate that the von Mises stress will significantly decrease and the equivalent creep strains will increase, when the degradation of Young’s modulus of fuel skeleton is considered. 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.

Keywords: Young's modulus degradation, fission gas bubbles, U-10Mo fuel skeleton, porosity