First-principles calculation and experimental study of oxygen diffusion in uranium dioxide

Dorado, Boris; Garcia, Philippe; Carlot, G.; Davoisne, Carine; Fraczkiewicz, M.; Pasquet, B.; Freyss, Michel; Valot, C.; Baldinozzi, Gianguido; Siméone, David; Bertolus, Marjorie

doi:10.1103/physrevb.83.035126

Cited by 120 publications

(87 citation statements)

References 46 publications

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“…Sabioni reports a grain boundary diffusion coefficient five orders of magnitude greater than the volume diffusion coefficient between 1773 K and 1973 K in a reducing atmosphere. 6 In addition, it has been shown in previous work relating to oxygen self-diffusion 7,8 that one of the issues in obtaining a reliable set of data lies in monitoring the relevant thermodynamic conditions during the experiment, such as oxygen partial pressure, temperature and the impurity content of the sample.…”

Section: -4mentioning

confidence: 99%

“…It is now recognized that the DFT+U method creates a number of metastable states that make the search for the electronic ground state difficult and can lead to large errors in calculations of defect energies if no care is taken to control the correlated electronic states. To our knowledge, there are currently three methods to circumvent these difficulties: the occupation matrix control (OMC) scheme, 8,[21][22][23][24][25][26] the U -ramping method, 27 and the quasi-annealing method.…”

Section: -15mentioning

confidence: 99%

“…It was first developed by Jomard et al 23 and Amadon et al 24 then applied to uranium dioxide. 8,21,22,25 Compared to the U -ramping method or the QA approach, the OMC scheme allows us to more precisely control various valence states for uranium atoms in defective UO 2 , such as U…”

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confidence: 99%

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First-principles calculations of uranium diffusion in uranium dioxide

et al. 2012

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The present work reports first-principles DFT+U calculations of uranium self-diffusion in uranium dioxide (UO2), with a focus on comparing calculated activation energies to those determined from experiments. To calculate activation energies, we initially formulate a point defect model for UO2±x that is valid for small deviations from stoichiometry. We investigate five migration mechanisms and calculate the corresponding migration barriers using both the LDA+U and GGA+U approximations. These energy barriers are calculated using the occupation matrix control scheme that allows one to avoid the metastable states that exist in the DFT+U approximation. The lowest migration barrier is obtained for a vacancy mechanism along the 110 direction. This mechanism involves significant contribution from the oxygen sublattice, with several oxygen atoms being displaced from their original position. The 110 vacancy diffusion mechanism is predicted to have lower activation energy than any of the interstitial mechanisms and comparison to experimental data for stoichiometric UO2 also confirms this mechanism.

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Section: -4mentioning

confidence: 99%

Section: -15mentioning

confidence: 99%

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First-principles calculations of uranium diffusion in uranium dioxide

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“…Although the experimental determination of migration energies is difficult, recent electronic structure calculations using DFT + U show a reasonable agreement for the migration energies of oxygen interstitials and vacancies. 41 The corresponding data for uranium are, however, more difficult to obtain experimentally as well as theoretically.…”

Section: B Defect Migration Energiesmentioning

confidence: 99%

Frenkel pair recombinations in UO2: Importance of explicit description of polarizability in core-shell molecular dynamics simulations

2012

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The oxygen and uranium Frenkel pair (FP) recombination mechanisms are studied in UO 2 using an empirical interatomic potential accounting for the polarizability of the ions, namely a dynamical core-shell model. The results are compared to a more conventional rigid-ion model. Both model types have been implemented into the CP2K program package and thoroughly validated. The overall picture indicates that the FP recombination mechanism is a complex process involving several phenomena. The FP recombination can happen instantaneously when the distance between the interstitial and the vacancy is small or can be thermally activated at larger separation distances. However, other criteria can prevail over the interstitial-vacancy distance. The surrounding environment of the FP defect, the mechanical stiffness of the matrix, and the orientation of the migration path are shown to be major factors acting on the FP lifetime. The core-shell and rigid-ion models provide a similar qualitative description of the FP recombination mechanism. However, the FP stabilities determined by both models significantly differ in the lower temperature range considered. Indeed, the recombination time of the oxygen and uranium FPs can be up to an order of magnitude lower in the core-shell model at T = 600 K and T = 1800 K, respectively. These differences highlight the importance of the explicit description of polarizability on some crucial properties such as the resistance to amorphization. This refined description of the interatomic interactions would certainly affect the description of the recrystallization process following a displacement cascade. In turn, the self-healing phase would be better accounted for in the core-shell model and the misestimate inherent to the lack of polarizability in the rigid-ion model corrected.

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“…The migration barriers for anion vacancies and interstitials are 0.5 [39,42] and 0.9-1.3 eV [39,42,43], respectively, while the lowest barrier for cations (a cluster of two U vacancies that can form under irradiation) is predicted to be 2.6 eV [4] and the barrier for migration of single U vacancies is 4.5-4.8 eV [4,38].…”

Section: Oxygen Interstitials and Vacanciesmentioning

confidence: 99%

Mesoscale Benchmark Demonstration Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing

Li¹,

Hu²,

Montgomery³

et al. 2012

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SUMMARYA study was conducted to evaluate the capabilities of different numerical methods used to represent microstructure behavior at the mesoscale for irradiated material using an idealized benchmark problem. The purpose of the mesoscale benchmark problem was to provide a common basis for assessing several mesoscale methods to identify the strengths and areas of improvement in the predictive modeling of microstructure evolution. In this work, mesoscale models (phase-field, Potts, and kinetic Monte Carlo) developed by Pacific Northwest National Laboratory, Idaho National Laboratory, Sandia National Laboratory, and Oak Ridge National Laboratory were used to calculate the evolution kinetics of intragranular fission gas bubbles in UO 2 fuel under post-irradiation thermal annealing conditions. The benchmark problem was constructed to include important microstructural evolution kinetics of intragranular fission gas bubble behavior, such as the atomic diffusion of Xe atoms, U vacancies, and O vacancies; the effect of vacancy capture and emission from defects; and the elastic interaction on nonequilibrium gas bubbles. An idealized set of assumptions and a common set of thermodynamic and kinetic data were imposed on the benchmark problem to simplify the mechanisms considered. The modeling capabilities of different methods are compared against selected experimental and simulation results. These comparisons find that while the phase-field methods and Potts kinetic Monte Carlo methods are able to incorporate several of the mechanisms that influence intra-granular bubble growth and coarsening, the Potts model is challenged by the low solubility and long-range diffusion necessary to simulate this problem correctly. The statistical-mechanical nature of Potts kMC requires large ensembles with long simulation times to treat this problem. Future efforts are recommended to construct increasingly more complex mesoscale benchmark problems to further verify and validate the predictive capabilities of the mesoscale modeling methods used in this study.

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First-principles calculation and experimental study of oxygen diffusion in uranium dioxide

Cited by 120 publications

References 46 publications

First-principles calculations of uranium diffusion in uranium dioxide

First-principles calculations of uranium diffusion in uranium dioxide

Frenkel pair recombinations in UO2: Importance of explicit description of polarizability in core-shell molecular dynamics simulations

Mesoscale Benchmark Demonstration Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing

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