Vacancies, interstitials and gas atoms in beryllium

Ganchenkova, Maria; Vladimirov, P.; Бородин, В. А.

doi:10.1016/j.jnucmat.2008.12.063

Cited by 41 publications

(40 citation statements)

References 15 publications

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“…This indicates that in-plane migration is energetically preferred, in agreement with the previous theoretical result of Ganchenkova et al, 27 where it was suggested that helium atoms might diffuse faster in the xy basal plane than along the c direction. Although our calculated energy barrier of 0.026 eV is slightly lower than their value of 0.1 eV, 27 it is probably due to different calculation settings. The lattice vibrational energy also plays a valuable role in the total migration energy, especially in the range of high temperature.…”

Section: B Migration Energy Barriers Of Helium In α-Be Crystalsupporting

confidence: 91%

“…The energy profile resembles a sinusoidal curve with the migration barrier of 0.328 eV, as shown in fig. 4(a), which is comparable to previous theoretical values of 0.36 eV 27 and 0.37 eV. 18 As to the path of two nearest-neighbor BT sites, the CI-NEB calculations directly show that the migration energy barrier is 0.331 eV as demonstrated in Fig.…”

Section: B Migration Energy Barriers Of Helium In α-Be Crystalsupporting

confidence: 86%

“…10 But compared with another earlier prediction (Ref. 27) in which helium at BO site is energetically more favorable than at BT site as shown in Table I, the discrepancy is quite pronounced. Since the TABLE I.…”

Section: A Equilibrium Position Of Interstitial Helium In α-Bementioning

confidence: 64%

“…Cell size 96-atom cell 96-atom cell 27 96-atom cell 18 128-atom cell 18 E cut (eV) 600 300 450 450 k points 9 × 9 × 9 9 × 9 × 9 13 × 13 × 13 13 ), which makes interstitial helium energetically unfavorable.…”

Section: Current Results Previous Resultsmentioning

confidence: 99%

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First-principles study of migration and diffusion mechanisms of helium in α-Be

Yang

et al. 2016

AIP Advances

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The behavior of interstitial helium in α-Be has been studied with first-principles method. It is found that the most favored position for helium is the basal octahedral (BO) site, closely followed by the basal tetrahedral (BT) site, in agreement with previous predictions. The interaction energy between the helium and the neighborhood Be atoms and the deformation energy of α-Be matrix are calculated. The feasible minimum-energy pathways (MEP) of interstitial helium atoms in α-Be matrix and the corresponding atomic structures of the saddle points associated with the each MEP are investigated. The temperature-dependent diffusion coefficients have also been predicted. It is confirmed that the interstitial helium diffuses two-dimensionally at low temperatures; however, it can diffuse three-dimensionally at higher temperatures. Besides, the microscopic parameters in the pre-factor and activation energy of the diffusion coefficients are obtained. Both diffusion coefficients are higher than the available experiment data, which may attribute to the fact that under real condition the diffusion is not free, i.e. the actual α-Be matric has various defects and impurities which heavily affect the diffusion of helium. Therefore, our theoretical prediction is the upper bound for helium diffusion in α-Be matrix.

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Section: B Migration Energy Barriers Of Helium In α-Be Crystalsupporting

confidence: 91%

Section: B Migration Energy Barriers Of Helium In α-Be Crystalsupporting

confidence: 86%

Section: A Equilibrium Position Of Interstitial Helium In α-Bementioning

confidence: 64%

Section: Current Results Previous Resultsmentioning

confidence: 99%

See 2 more Smart Citations

First-principles study of migration and diffusion mechanisms of helium in α-Be

Yang

et al. 2016

AIP Advances

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“…One work [11] presents computational data on the energy of the system when vacancies, interstices, and gas atoms (He, H) are introduced. Specifically, it is shown that the formation of vacancy complexes (di-, tri-vacancies) is energetically unfavorable, while for helium introduced into a beryllium lattice there are two energetically favorable positions in the basal plane.…”

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confidence: 99%

State of helium in irradiated beryllium

Kosenkov¹,

Posevin²,

Silantiev³

2012

At Energy

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Experimental data are presented on the change of the pycnometric density and unit-cell volume of beryllium irradiated in an SM reactor to neutron fluence 14·10 22 cm -2 . The behavior of the unit-cell volume as a function of the neutron fluence is similar to the data for other metals. This and data on the volume change in beryllium oxide, where a large amount of gas is also formed during irradiation, make it possible to evaluate critically the assertion that helium forms a solid substitution solution. It is proposed that helium is confined in small accumulations.The unique nuclear-physical and physical-mechanical properties of beryllium make this element irreplaceable as a material for neutron moderators and reflectors. Numerous studies of beryllium articles and specially prepared samples irradiated to neutron fluence >10 23 cm -2 (E > 0.1 MeV) have now been performed. The changes in the material properties, information on which is needed to establish safe service lifetimes, have been studied. One such property is swelling -an increase of the volume of an article and decrease of the pycnometric density.It is well known that the swelling of irradiated materials can be substantial. Under irradiation, the density AlGdO 3 , Dy 2 TiO 5 , and BN changes by 6.5, -4.2, and ~30%, respectively [1]. The pycnometric density of diamond decreases to 47% and the unit-cell volume increases by 20% (up to the moment of amorphization) [2]. The masonry graphite at the Leningradskaya nuclear power plant showed a 13% reduction of the pycnometric density and the density measured according to the change in volume of the unit cell. It is known that corrosion resistant steel can swell by 20% under certain conditions. Aside from structural changes swelling can be due to vacancy accumulation and a change of the coordination number and therefore the character of the bonding force at the site of a single defect (vacancy or interstitial), for example, the model of the appearance of "graphite structure motifs" in diamond [3]. In these cases, large swelling was determined by the intrinsic defects of the material -components of Frenkel pairs, which arise as a result of the interaction of fast neutrons with the crystal lattice. Aside from Frenkel pairs, helium and tritium form in beryllium-containing materials. For example, the concentration of helium atoms is 12000 ppm, i.e., 1.2%, under fluence 6·10 22 cm -2 (E > 0.1 MeV) and increases to 1.7% under fluence 13·10 22 cm -2 [4]. Where is this helium? How does it affect swelling?Researchers studying beryllium oxide, which can be used as a reflector and moderator, were also faced with this problem. Extensive research done on BeO at the Research Institute for Atomic Reactors (NIIAR) has shown that 16% swelling under irradiation to fluence 1·10 22 cm -2 (irradiation temperature <200°C) is "solid," because the relative increase of the volume of the material is equal to the relative increase of the unit-cell volume. In addition, there are no grounds for attributing it to helium accumulation. Figure 1 sh...

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