Revisiting the diffusion mechanism of helium in UO2: A DFT+U study

Liu, X.-Y.; Andersson, David

doi:10.1016/j.jnucmat.2017.10.066

Cited by 16 publications

(13 citation statements)

References 47 publications

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“…However, the values of this incorporation energy are still under debate. Indeed, the data found with first principle calculations (mainly DFT) are considerably variable [29][30][31][32][33]. Nonetheless, one general trend can be extracted: the He incorporation energy in OIS is the smallest ; hence OIS seems to be the most stable crystallographic position for the He atoms.…”

Section: Interatomic Potentialmentioning

confidence: 99%

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A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Brutzel

Chartier

2019

Journal of Nuclear Materials

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Molecular dynamics simulations have been carried out to determine the equation of state of helium inside nanobubbles embedded into a UO 2 matrix. The parameters of the equation of state are fitted with the Brearley and MacInnes hard-sphere model based on the formalism of Carnahan-Starling used in fuel performance codes. This new equation of state takes into account the interactions between the surrounding UO 2 matrix and the helium atoms. Four nanobubble sizes (diameters: 1, 2, 5, and 10 nm) have been investigated over four temperatures (300, 500, 700, and 900 K) and for initial helium concentration inside the bubble ranging from 0.33 × 10 5 to 3.9 × 10 5 mol.m −3 (corresponding to helium-to-vacancy ratio of 0.3 to 3.3, respectively). We find that helium atoms are inhomogeneously distributed inside the bubble. A boundary layer of 1 nm thickness appears at the bubble surface in which helium atoms are more concentrated and diffuse into the UO 2 matrix. We also find a saturation concentration of the helium atoms that can be incorporated into the bubble. This concentration limit is equal to 1.6 helium atom per vacancy in UO 2 . It corresponds to an atomic volume of 7.8 × 10 −30 m 3 , which is almost half of the value proposed with the original Brearley and MacInnes model (13 × 10 −30 m 3 ). For this threshold concentration and for bubble of diameter higher than 5 nm, nano-cracks and dislocations appear at the bubble surface. However, experimental observation is needed to confirm this finding. We calculated the critical pressures inside the bubble which yields to this onset of crack in UO 2 . These critical pressures are in good agreement with those calculated with the Griffith criterion for brittle fracture.

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Section: Interatomic Potentialmentioning

confidence: 99%

“…Values of the incorporation energies of He into octahedral interstitial sites (OIS), uranium vacancy (VU), and oxygen vacancy (VO) of the UO 2 matrix calculated with Grimes[19] and Yakub[16] potentials. They are compared with the range of values calculated with DFT[29][30][31][32][33].…”

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confidence: 99%

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Brutzel

Chartier

2019

Journal of Nuclear Materials

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“…Oxygen vacancy assisted helium migration has been found to be the energetically favourable mechanism in UO 2 with energy barriers comparable to this work. 30,31,46,47 Under helium infusion conditions in UO 2 , in which vacancy concentrations are low, the atomic diffusion of helium has been found to be much slower than in radiation damaged materials, 48,49 supporting the theory that helium migration is vacancy assisted.…”

Section: Migration Pathwaysmentioning

confidence: 92%

“…Oxygen vacancy assisted inter-site hopping has also been found to be the main diffusion mechanism of He in UO 2 . 30,31,47 3.3.1 Schottky defect inclusion. Structures with different concentrations of Schottky were generated by randomly removing atoms corresponding to missing PuO 2 concentrations of 0.5, 2 and 4% after which the system was relaxed.…”

Section: Helium Diffusion Calculationsmentioning

confidence: 99%

Atomistic simulation of helium diffusion and clustering in plutonium dioxide

Murray

Zhou

Slater

et al. 2022

Phys. Chem. Chem. Phys.

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“…Uranium dioxide, extensively studied in Refs. [10,[38][39][40][41][42][43][44][45][46][47][48][49], continues attracting considerable attention as the scope of ab initio methods expands to enable the treatment of defects [50] and their diffusion [51][52][53], given that defects and their diffusion contribute to the overall performance of UO 2 nuclear fuel. The magnetic ground state of bulk crystalline UO 2 has been investigated experimentally and theoretically [10, 38-42, 49, 54], and there is extensive information about the surface structure of UO 2 derived from elevated temperature scanning tunneling microscope observations [55][56][57].…”

Section: Introductionmentioning

confidence: 99%

Parametrization of LSDA+U for noncollinear magnetic configurations: Multipolar magnetism in UO2

Dudarev

Liu

Andersson

et al. 2019

Phys. Rev. Materials

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To explore the formation of noncollinear magnetic configurations in materials with strongly correlated electrons, we derive a noncollinear LSDA+U model involving only one parameter U, as opposed to the difference between the Hubbard and Stoner parameters U − J. Computing U in the constrained random phase approximation, we investigate noncollinear magnetism of uranium dioxide UO 2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO 2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f -orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the noncollinear 3k state, which has the lowest energy even in an undistorted lattice. The choice of parameter U in the LSDA+U model has a notable quantitative effect on the predicted properties of UO 2 , in particular on the magnetic exchange interaction and, perhaps trivially, on the band gap: The value of U = 3.46 eV computed fully ab initio delivers the band gap of 2.11 eV in good agreement with experiment, and a balanced account of other pertinent energy scales. * sergei.dudarev@ukaea.uk † cesare.franchini@univie.ac.at. (6) Here,N = m,σĉ † m,σĉm,σ is the operator of the total number of electrons on a site,n kl = σĉ † k,σĉ l,σ , and M = m,ξ,ξ ′ĉ † m,ξ σ ξξ ′ĉ m,ξ ′

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Revisiting the diffusion mechanism of helium in UO2: A DFT+U study

Cited by 16 publications

References 47 publications

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

Atomistic simulation of helium diffusion and clustering in plutonium dioxide

Parametrization of LSDA+U for noncollinear magnetic configurations: Multipolar magnetism in UO2

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