Bulk and surface diffusion of neodymium in alpha-uranium: Ab initio calculations and kinetic Monte Carlo simulations

A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and kinetic Monte Carlo (KMC) study of the bulk diffusivity of Nd in alpha-U, fully taking into account the effect of radiation enhanced diffusion. The vacancy mechanism is considered to be the dominant mechanism for the bulk diffusion of Nd since a Nd interstitial is found to be intrinsically unstable in alpha-U. The surface diffusivity of a Nd adatom on alpha-U (001) surface has been further predicted using KMC simulations parameterized by DFT calculations. The present study suggests that Nd transport via the surface diffusion mechanism can be many orders of magnitude faster than bulk diffusion. Furthermore, the results from the present lower length scale study can be used to inform mesoscale phase-field simulations to determine the effective diffusion coefficient of Nd through alpha-U with a porous microstructure. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the transport of Nd in α-U using ab initio density functional theory and kinetic Monte Carlo methods. It finds that Nd transport via surface diffusion mechanism can be significantly faster than bulk diffusion. These findings can inform further research on modeling fuel-cladding chemical interaction.