Mechanism for transient migration of xenon in UO2

In this letter, we report recent work on atomistic modeling of diffusion migration events of the fission gas product xenon in UO2 nuclear fuel. Under nonequilibrium conditions, Xe atoms can occupy the octahedral interstitial site, in contrast to the thermodynamically most stable uranium substitutional site. A transient migration mechanism involving Xe and two oxygen atoms is identified using basin constrained molecular dynamics employing a Buckingham type interatomic potential. This mechanism is then validated using density functional theory calculations using the nudged elastic band method. An overall reduction in the migration barrier of 1.6–2.7 eV is obtained compared to vacancy-mediated diffusion on the uranium sublattice.

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