Diffusional creep model in UO2 informed by lower-length scale simulations

COT Galvin and DA Andersson and RT Sweet and L Capolungo and MWD Cooper, JOURNAL OF NUCLEAR MATERIALS, 607, 155659 (2025).

DOI: 10.1016/j.jnucmat.2025.155659

Creep is an important deformation mode for nuclear fuel performance as it influences the pellet-cladding gap, which in turn affects the fuel temperature. It also impacts the cladding stress due to cladding-pellet mechanical interactions. Having a creep model that captures the correct mechanisms is essential for the accurate physical fidelity of nuclear fuel performance codes. We present a diffusional creep model for UO2 that has been informed using lower-length scale simulations. The simulations focus on the uranium vacancy concentration, diffusivity, and elastic dipole tensor, all of which underpin steady-state and transient diffusional creep in UO2. The results were compared against available experimental creep values and used to provide insight as to the likely role of uranium self-diffusion due to vacancies at grain boundaries. In this study, we also determine the dominant diffusional creep mechanism for UO2, and conclude that it is the Coble mechanism. Furthermore, the development of a creep model in general is an important first step towards modeling the complicated irradiation case, and is needed to support extension of the model to microstructures that have limited data, such as UO2 with enlarged grains due to dopants.

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