The role of dopant charge state on defect chemistry and grain growth of doped UO2

Cooper, M.W.D.; Stanek, C. R.; Andersson, David

doi:10.1016/j.actamat.2018.02.020

Cited by 55 publications

(29 citation statements)

References 92 publications

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“…The computed value of Hubbard U parameter for Cr in Cr 2 O 3 (i.e., Cr 3+ ) is 4.0 eV, which is consistent with the one used in previous studies of Cr-bearing systems (~3.5 eV, e.g., refs. 6,[18][19][20][21] ). For Cr 2+ we used the value of 6.5 eV, which we derived for CrO.…”

Section: Resultsmentioning

confidence: 99%

“…The density functional theory (DFT)-based first principles studies of Middleburgh et al 12 consider formation of Cr 3+ as dominant Cr species in the same structural arrangement as resulted from the force-field simulations, and discuss a less energetically favorable scenario of Cr 4+ . The more recent ab initio studies of Cooper et al 6 show the possibility of Cr in "+1" oxidation state. Interestingly, the "+2" state has never been considered as dominant at ambient or hightemperature synthesis conditions (T> 1500 K).…”

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confidence: 97%

“…The impact of Cr doping on the performance of UO 2 matrix depends also on the oxidation state of Cr in the nuclear fuel, which is claimed to be Cr 3+ 4,5 . Other oxidation states, however, are not excluded 6,7 . In particular, by analyzing X-ray absorption spectrum of Cr-doped UO 2 Mieszczynski et al 7 suggest existence of Cr 2+ , but express a need for the electronic structure calculations to confirm such a possibility.…”

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confidence: 99%

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The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

2020

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Doping by Cr is used to improve the performance of uranium dioxide (UO 2)-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 UO 2-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr doped UO 2 matrix. We unexpectedly found that Cr in UO 2 exists as Cr 2+ species and not as the widely claimed Cr 3+. 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 UO 2 is given by a pair of associated Cr 2+ 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.

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Section: Resultsmentioning

confidence: 99%

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confidence: 97%

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confidence: 99%

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The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

2020

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“…The slightly increased lattice parameter induced by Cr-doping is somewhat unexpected since the radius of the Cr 3+ ion (0.615 Å) is smaller than that of U 4+ (1.03 Å); therefore if Cr were incorporated in the UO2 lattice, a decrease of the lattice parameter of UO2 should be expected [13]. Such an increase might be due to incorporation of Cr into UO2 in a different valence state, as predicted by [14]. Indeed, the ionic radii of Cr 1+ and Cr 2+ are 1.09 Å and 0.89 Å, respectively; the presence of a reduced form of Cr, induced by the reducing conditions during the HIP synthesis, may result in an increase of the lattice size.…”

Section: Chemical Characterisationmentioning

confidence: 85%

Hot Isostatic Pressing (HIP): A novel method to prepare Cr-doped UO2 nuclear fuel

et al. 2020

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The addition of Cr2O3 to modern UO2 fuel modifies the microstructure so that, through the generation of larger grains during fission, a higher proportion of fission gases can be accommodated. This reduces the pellet-cladding mechanical interaction of the fuel rods, allowing the fuels to be “burned” for longer than traditional UO2 fuel, thus maximising the energy obtained. We here describe the preparation of UO2 and Cr-doped UO2 using Hot Isostatic Pressing (HIP), as a potential method for fuel fabrication, and for development of analogue materials for spent nuclear fuel research. Characterization of the synthesised materials confirmed that high density UO2 was successfully formed, and that Cr was present as particles at grain boundaries and also within the UO2 matrix, possibly in a reduced form due to the processing conditions. In contrast to studies of Cr-doped UO2 synthesised by other methods, no significant changes to the grain size were observed in the presence of Cr.

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“…Figures 2.2 and 2.3 show the comparisons of Bison integral FGR predictions to the experimental data from Halden[40] for IFA-677.1 rods 1 and 5, resepctively. Results are presented for simulations using the original Bison intra-granular fission gas model, which is based on epirical fits from[5] (gray lines), the new SciDAC fission gas model (black lines) and the new SciDAC model with the additional multiscale coupling to the atomistic calculations for fission gas atom diffusivity in Cr 2 O 3 doped UO 2 from LANL[42] (blue lines).…”

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M3MS-19IN0101201 Modeling Intra-granular Fission Gas Bubble Evolution in Uranium Dioxide during Transients

Pastore

2019

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The SciDAC milestone M3MS-19IN0101201 on Modeling Intra-granular Fission Gas Bubble Evolution in Uranium Dioxide during Transients was completed with the development, testing and implementation in the Bison code of an engineering model for intra-granular fission gas bubble evolution that is applicable to transient conditions. The model extends the previous work on modeling bubble evolution during normal operating conditions to include additional complexity that arises during transient situations, in particular, the so-called intra-granular bubble coarsening. This phenomenon refers to the appearance of a second population of coarsened bubbles with diameters of tens to hundreds of nm, which co-exist with nanometric bubbles present also during normal operating conditions and are responsible for a large portion of transient fuel swelling. The developed model considers growth of bubbles along dislocations, associated with the absorption of vacancies available in the dislocation core region, and favored by pipe diffusion of fission gas atoms. The model also utilizes the formulation for the gas atom resolution rate developed in the present SciDAC project through molecular dynamics simulations by other institutions. The present work therefore demonstrates an operational multiscale approach, based on collaboration within the project. The model is validated to an extensive experimental dataset of ramp tested uranium dioxide fuel samples. Additionally, we present new applications of the base model for bubble evolution during normal operating conditions to Bison engineering simulations of Cr 2 O 3-doped fuel rods irradiated in the Halden reactor. Simulation results in terms of integral fission gas release in the fuel rods are compared to the available experimental data, pointing out significant improvements in the engineering predictions compared to application of the empirical model that was available in Bison before the SciDAC developments. 2 Application of SciDAC model to Halden fuel rod simulations using Bison

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The role of dopant charge state on defect chemistry and grain growth of doped UO2

Cited by 55 publications

References 92 publications

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

Hot Isostatic Pressing (HIP): A novel method to prepare Cr-doped UO2 nuclear fuel

M3MS-19IN0101201 Modeling Intra-granular Fission Gas Bubble Evolution in Uranium Dioxide during Transients

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