Pathway and energetics of xenon migration in uranium dioxide

Abstract

Using a combination of Density Functional Theory (DFT), classical potentials, Molecular Dynamics (MD), and Nudged Elastic Band (NEB) calculations, we explore the diffusion of xenon in uranium dioxide (UO 2 ). We compare migration barriers of empirical potentials with DFT by performing NEB calculations and subsequently we use the DFT-validated empirical potentials to calculate vacancy clusters, with and without xenon, to determine the migration path and barrier of xenon in bulk UO 2 . We find (i) two empirical potentials out of four tested agree qualitatively with DFT derived energetics for Schottky defect migration, (ii) through the use of molecular dynamics with empirical potentials, we have found a new path for the diffusion of xenon-tetravacancy clusters (Xe + 2 V U + 2 V O ), (iii) this new path has an energy barrier significantly lower than previously reported paths by nearly 1 eV, (iv) we examine the physical contributions to the migration pathway and find the barrier is largely electrostatic and that xenon contributes very little to the barrier height, (v) once a uranium vacancy attaches to a xenonSchottky defect, the resulting xenon-tetravacancy cluster is strongly bound, and (vi) like xenon in a tetravacancy, a xenon-double Schottky defect can diffuse in a concerted manor with a comparable barrier to xenon in a tetravacancy, but two of the oxygen vacancies are only weakly bound to the defect.

Radiation damage in cubic ZrO2 and yttria-stabilized zirconia from molecular dynamics simulations

“…The vacancy clusters are charge neutral Schottky defects formed by accumulation of two V O •• around one V Zr ''''. These clusters are identical to those observed previously in CeO 2 and other similar systems [19,20,[23][24][25][26][27]. The interstitial clusters are a more complex defect types than vacancy clusters.One of the clusters highlighted inFigure 1bis shown inFigure 1c.…”

Molecular dynamics study of fission gas bubble nucleation in UO2

“…For He bubble nucleation in UO 2 simulations, a computational supercell of bulk UO 2 with density functional theory (DFT) calculations applying the DFT+U methodology [21][22][23] .…”

Transport properties in dilute UN(X) solid solutions (X=Xe,Kr)

“…The work on silicide [19][20][21][22] or carbide 23 is only starting but the work on oxide fuels has already received many contributions. It is outside the scope here to mention all of them, but Xe has been studied in U O 2 24 , other actinide oxide fuels 25 , and its diffusion following complex paths has also been investigated 26 , as well as the effect of nonstoichiometry and irradiation conditions on its diffusion properties 27 .However, krypton has never been considered in such works either for UN, except when swelling was the sole phenomenon being investigated 17 . Even in some fuel performance codes, Xe and Kr are assumed to have the same coefficient 28 , an assumption that merits verification.…”