First study of uranium self-diffusion in UO2 by SIMS

Sabioni, Antônio Claret Soares; Ferraz, Wilmar Barbosa; Millot, F.

doi:10.1016/s0022-3115(98)00482-6

Cited by 62 publications

(39 citation statements)

References 15 publications

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“…In general, the strong influence of temperature-independent anionic defects on the diffusion activation energy, confirmed by our simulation of non-stoichiometric uranium dioxide, allow explaining the large scatter of the available experimental dependences [50,52,2,11] by lack of continuous control of stoichiometry and different concentration of temperature-independent defects of all types.…”

Section: Cation Diffusion In Non-stoichiometric Uranium Dioxidesupporting

confidence: 71%

“…In the most recent experimental work on cation diffusion measurement in single crystals of UO 2 [11] the absence of grain boundaries and concentration of impurities were carefully checked, but the presence of dislocations was not discussed. In addition to lowering the activation energy, this hypothesis can also explain the fact that the uranium diffusion coefficients in different studies vary by several orders of magnitude: their samples may differ by the temperature-independent defect concentration.…”

Section: /S) It Ap-mentioning

confidence: 99%

“…In the existing ''low-temperature'' experiments (see [2,11]) a variety of methods were used, including direct (using radioactivity) and indirect (using data on the kinetics of sintering) approaches. At that, the published results have significant variation (three orders of magnitude of the uranium diffusion coefficient counting results for single crystals only).…”

Section: Introductionmentioning

confidence: 99%

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Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Boyarchenkov

Potashnikov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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a b s t r a c tThis article is devoted to investigation of cation self-diffusion mechanisms, taking place in UO 2 , UO 2+x , and UO 2Àx crystals simulated under periodic (PBC) and isolated (IBC) boundary conditions using the method of molecular dynamics in the approximation of rigid ions and pair interactions. It is shown that under PBC the cations diffuse via an exchange mechanism (with the formation of Frenkel defects) with activation energy of 15-22 eV, while under IBC there is competition between the exchange and vacancy (via Schottky defects) diffusion mechanisms, which give the effective activation energy of 11-13 eV near the melting temperature of the simulated UO 2.00 nanocrystals. Vacancy diffusion with lower activation energy of 6-7 eV was dominant in the non-stoichiometric crystals UO 2.10 , UO 2.15 and UO 1.85 . Observations showed that a cation vacancy is accompanied by different number of anion vacancies depending on the deviation from stoichiometry: no vacancies in UO 2.15 , single vacancy in UO 2.00 and four vacancies in UO 1.85 . The corresponding law of mass action formulas derived within the Lidiard-Matzke model allowed explaining the obtained activation energies and predicting a change in the activation energy within the temperature range of the superionic phase transition. The diffusion of cations on the surface of nanocrystals had activation energy of 3.1-3.6 eV.

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Section: Cation Diffusion In Non-stoichiometric Uranium Dioxidesupporting

confidence: 71%

Section: /S) It Ap-mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Boyarchenkov

Potashnikov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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“…The migration energies for uranium selfdiffusion in non-stoichiometric as well as stoichiometric UO 2 have been studied experimentally. [62][63][64][65] However, a detailed exploration of the defect energies, energy barriers and uranium migration paths has only been made possible recently by first-principles based density functional theory (DFT) calculations. [20][21][22][66][67][68] In this study, we use the work of Andersson et al 21 in which various charged single uranium vacancies and their clusters have been studied for UO 2−x , UO 2 and UO 2+x , both for intrinsic and irradiation conditions.…”

Section: A Migration Paths and Energy Barriersmentioning

confidence: 99%

Impact of homogeneous strain on uranium vacancy diffusion in uranium dioxide

et al. 2015

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We present a detailed mechanism of, and the effect of homogeneous strains on, the migration of uranium vacancies in UO2. Vacancy migration pathways and barriers are identified using density functional theory (DFT) and the effect of uniform strain fields are accounted for using the dipole tensor approach. We report complex migration pathways and non-cubic symmetry associated with the uranium vacancy in UO2 and show that these complexities need to be carefully accounted for to predict the correct diffusion behavior of uranium vacancies. We show that under homogeneous strain fields, only the dipole tensor of the saddle with respect to the minimum is required to correctly predict the change in the energy barrier between the strained and the unstrained case. Diffusivities are computed using kinetic Monte Carlo (KMC) simulations for both neutral and fully charged state of uranium single and di-vacancies. We calculate the effect of strain on migration barriers in the temperature range 800 -1800 K for both vacancy types. Homogeneous strains as small as 2% have a considerable effect on diffusivity of both single and di-vacancies of uranium, with the effect of strain being more pronounced for single vacancies than di-vacancies. In contrast, the response of a given defect to strain is less sensitive to changes in the charge state of the defect. Further, strain leads to anisotropies in the mobility of the vacancy and the degree of anisotropy is very sensitive to the nature of the applied strain field for strain of equal magnitude. Our results suggest that the influence of strain on vacancy diffusivity will be significantly greater when single vacancies dominate the defect structure, such as sintering, while the effects will be much less substantial under irradiation conditions where di-vacancies dominate.

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“…As is well known, a lot of studies of uranium (or plutonium) oxides and their solid solutions used as nuclear fuel materials have been performed for the thermal and mechanical properties so far. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, there are relatively few studies of americium oxides. This is caused by its radio-toxicity and chemical instability.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study on Grain Boundary Diffusion of Actinides and Oxygen in Oxide Fuels

Nishina

Yoshida

Arima

et al. 2011

Progress in Nuclear Science and Technology

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Diffusion phenomena of actinides and oxygen are relating to various properties of oxide fuels, e.g. actinide and oxygen redistribution, pore migration, sintering behavior. Although lots of experimental data have been obtained for U and O diffusions, these seem to be a little scattered among experiments. In addition, there are few studies of transuranium elements. Recently, we experimentally showed that diffusion coefficients of Am and Pu were almost comparable with that of U and the contribution of grain boundaries (GB) were relatively large in oxide fuels. On the other hand, the molecular dynamics (MD) calculation showed that U ions migrated via its vacancies and the O diffusion mechanism changed with temperature in bulk. In this study, the GB diffusion coefficients and the mechanism were systematically evaluated for U, Am and O in oxide fuels by MD calculations. For actinides and oxygen, their GB diffusion coefficients are significantly larger than bulk ones, and the diffusion mechanisms in GBs are almost independent on temperature. Furthermore, the GB diffusion is strongly dependent on its structure and the interfacial potential energy. The lower oxygen-to-metal (O/M) ratio gives the larger GB diffusion coefficients for actinides and oxygen.

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First study of uranium self-diffusion in UO2 by SIMS

Cited by 62 publications

References 15 publications

Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Impact of homogeneous strain on uranium vacancy diffusion in uranium dioxide

Molecular Dynamics Study on Grain Boundary Diffusion of Actinides and Oxygen in Oxide Fuels

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