Abstract
Doping by Cr is used to improve the performance of uranium dioxide (UO2)-based nuclear fuel. However, the mechanism of structural incorporation of Cr remains unclear. Here, in order to understand this process on the atomic scale and the redox state of Cr in UO2-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr doped UO2 matrix. We unexpectedly found that Cr in UO2 exists as Cr2+ species and not as the widely claimed Cr3+. We re-evaluated previously published x-ray absorption near edge structure spectroscopy data and confirmed the computed redox state of Cr. Thermodynamic consideration shows that the favorable structural arrangement of Cr in UO2 is given by a pair of associated Cr2+ and oxygen vacancy. The realism of this doping mechanism is further demonstrated by a match to the measured maximum Cr solubility and small lattice contraction.
Highlights
Doping by Cr2O3 UO2 (Cr) is used to improve the performance of uranium dioxide (UO2)-based nuclear fuel
The impact of Cr doping on the performance of UO2 matrix depends on the oxidation state of Cr in the nuclear fuel, which is claimed to be Cr3+ 4,5
The same value we were getting for Cr2+ in UO2 and we observed that the derived Hubbard U parameter depends strongly on the Cr oxidation state, but is weakly dependent on the local environment of Cr
Summary
Doping by Cr is used to improve the performance of uranium dioxide (UO2)-based nuclear fuel. In order to understand this process on the atomic scale and the redox state of Cr in UO2-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr doped UO2 matrix. The impact of Cr doping on the performance of UO2 matrix depends on the oxidation state of Cr in the nuclear fuel, which is claimed to be Cr3+ 4,5. The atomistic modeling studies have been used to understand the incorporation of Cr into the UO2 matrix at atomic level Most of these studies used force-fields approach, in which interatomic interactions are represented by analytical functions and charge/oxidation states of the involved species are fixed[10], for chromium atom to Cr3+ 1,11,12. The real oxidation states are not always well constrained, but could be conclusively deducted by a combination of
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