Enhanced diffusion under alpha self-irradiation in spent nuclear fuel: Theoretical approaches

Various theoretical approaches have been developed in order to estimate the enhanced diffusion coefficient of fission products under alpha self-irradiation in spent nuclear fuel. These simplified models calculate the effects of alpha particles and recoil atoms on mobility of uranium atoms in UO₂. They lead to a diffusion coefficient which is proportional to the volume alpha activity with a proportionality factor of about 10⁻⁴⁴ (m⁵). However, the same models applied for fission lead to a radiation-enhanced diffusion coefficient which is approximately two orders of magnitude lower than values reported in literature for U and Pu. Other models are based on an extrapolation of radiation-enhanced diffusion measured either in reactors or under heavy ion bombardment. These models lead to a proportionality factor between the alpha self-irradiation enhanced diffusion coefficient and the volume alpha activity of 2 × 10⁻⁴¹ (m⁵).