•The Al-terminated Σ13 grain boundary in α-Al2O3 is a fast diffusion channel for H.•Cr atoms tend to segregate to this boundary.•The exist of Cr atoms can suppress the diffusion of H along this boundary.To acquire knowledge of the effect of chromium dopant bringing on hydrogen diffusion along grain boundaries (GBs) of α-Al2O3, the energetics and mobility of hydrogen along Σ13 GB with and without Cr dopant have been studied via the first-principles calculations with the projector-augmented wave method. The energy barriers for hydrogen diffusion before and after Cr doped on Al-terminated Σ13 GB are determined to be 0.69 eV and 1.09 eV, respectively, which is smaller than or close to the hydrogen bulk diffusion with an activation energy of 1.10 eV. The results suggest that before doping Cr atoms, there is a rapid and easy diffusion channel for hydrogen along the Σ13 GB. However, the calculations show the segregation of Cr atoms to the GB is energetic favorable with a segregation energy of −0.39 eV/atom, and the existence of Cr can suppress hydrogen diffusion along the Al-terminated Σ13 GB.

•The pioneer study on the diffusion of hydrogen along grain-boundary of in α-Al2O3.•Explaining the difference between experiment and calculated PRF value.•Providing a method for alumina using as a TPB that is treated by irradiation.We have studied the energetics and mobility of hydrogen in the bulk and along the rhombohedral Σ7 grain boundary (GB) of α-Al2O3 via first-principles calculations based on the projector-augmented wave method. The temperature-dependent diffusivities D(T) in the α-Al2O3 bulk and along the Σ7 GB are derived. The ratio shows that the diffusivity along the GB is 2–5 orders of magnitude greater than in the bulk at temperatures in the range of 273–973 K, revealing that the diffusion along the GB is the underlying reason for the experimentally observed permeation reduction factor being much lower than the anticipated value. Moreover, the calculations also reveal that radiation-induced O vacancies tend to aggregate to the GB plane, thereby forming a zigzag O vacancy chain. In such circumstances, however, the calculated migration energy for hydrogen diffusion along the O vacancy chain is 2.58 eV, which is much greater than that of 1.10 eV and 0.81 eV for H diffusion in the bulk and along the GB, respectively. This finding suggests that O vacancies in the GB trap hydrogen atoms and prevent their diffusion along the GB.

•DFT calculations are used to study hydrogen diffusion behavior in OsO2 and RuO2.•Hydrogen diffusion activation energies are 0.793 eV and 0.659 eV in OsO2 and RuO2.•Vacancy behavior and hydrogen-vacancy interactions are investigated.•Vacancy defects tend to aggregate together.•Binding energies of H atoms may promote vacancy formation in RuO2.The behavior of atomic hydrogen in osmium dioxide and ruthenium dioxide is investigated through ab initio calculations using density functional theory. Interstitial hydrogen behaves as a donor in both metal oxides and only has one stable interstitial position, bonding with an O atom to form an OHO defect. The rates of diffusion parallel to the c-axis are estimated to be 3.95 × 10−7exp(−0.793/kBT) m2/s and 3.64 × 10−7exp(−0.659/kBT) m2/s in OsO2 and RuO2, respectively. The rates of diffusion perpendicular to the c-axis are estimated to be 1.80 × 10−6exp(−0.941/kBT) m2/s and 1.10 × 10−6exp(−1.21/kBT) m2/s in OsO2 and RuO2, respectively. Additionally, the binding energy of multiple H atoms in (O, Os, Ru) vacancies have been calculated. High binding energies of hydrogen in metal vacancies result in multiple H atoms associating with a single metal vacancy. In RuO2, the binding energy of multiple H atoms outweighs the formation energy of a single Ru vacancy as well as that of a Ru–O divacancy.

Oxide dispersion strengthened (ODS) ferritic steels are perceived as the most promising structural materials for advanced fission- and future fusion-reactor applications owing to their excellent irradiation resistance and high-temperature mechanical properties. To understand the role of interfaces under irradiation, the first-principles calculations have been performed to investigate geometric, energetic and electronic properties of the {1 0 0}<1 0 0>Fe//{1 0 0}<1 0 0>Y2O3 interface as well as their interaction with radiation point defects. For O monovacancy in the Y2O3 layer, its formation energy slightly increases when it approaches to interface. For Fe monovacancy, the vacancy formation energy decreases when the vacancy is close to the interface. For Fe–Fe divacancies, the formation energy of the first nearest neighbor (1NN) and 2NN Fe–Fe divacancies at the interface are −9.48 eV and −10.49 eV, while their binding energies are −2.46 eV and −1.45 eV, respectively. These results suggest that the α-Fe/Y2O3 interface tends to attract vacancies in Fe matrix, yet prevents to form voids at the interface, which enhances radiation resistance of ODS steels.

The adsorption behaviors of radioactive Cesium and Iodine nuclides on the graphitic surface in the high temperature gas-cooled reactor have been studied by the first-principles and statistic physics. It turns out that Cs atom prefers to be absorbed at the hollow of carbon hexagonal cell by 1.44 eV while I atom likes to site on the vertex of the hexagonal cell, right above carbon atoms with the adsorption energy of 0.54 eV. Electronic structure analysis reveals that Cs donates 0.81e of its 6s and 5p states to graphite substrate while the 5p state of I accepts 0.5e from carbon atoms. The variation of adsorption rate of Cs and I atoms with temperature and pressure is presented using a model of grand canonical ensemble.

The properties of simple point defect (i.e. vacancy, self and foreign interstitial atoms) in the hcp (alpha) and bcc (beta) Zr with trace solute Nb have been studied by ab initio calculations with VASP codes. The calculations indicate that the formation energies of vacancy and substitutional Nb atom are 1.94 eV and 0.68 eV in alpha Zr and 0.36 eV and 0.07 eV in beta Zr, respectively, while the binding energies of the nearest neighbor vacancy–substitutional Nb pair and the nearest neighbor substitutional Nb–Nb pair are 0.09 eV and 0.03 eV in alpha Zr and 2.78 eV and 0.72 eV in beta Zr, respectively. These results suggest that the Nb atoms are more likely to agglomerate and form precipitates in the beta Zr than in the alpha Zr. Thus, the α-Zr–β-Zr–β-Nb transition mechanism through in situ α to β transformation of Zr and the vacancy-assisted Nb diffusion for Nb conglomeration in beta Zr under irradiation is proposed to explain the existence of beta Nb and Zr precipitate mixtures observed in the experiments for the Zr–Nb alloy. In addition, the defect formation energies in bcc Nb are also presented.

Helium migration behavior in the bulk and along the rhombohedral Σ7 grain boundary (GB) of α-Al2O3 has been studied via first-principles calculations based on the projector-augmented wave method. It turns out that the formation energies of helium in the α-Al2O3 bulk and in the rhombohedral Σ7 GB area are 2.12 eV and 3.15 eV, respectively. The energy barrier for helium migration in bulk is 2.28 eV, indicating that helium is difficult to diffuse. Moreover, the calculations also reveal that the radiation-induced O vacancies are favored to aggregate to the Σ7 GB plane, forming a zigzag O vacancy chain. In such circumvent, however, the energy barrier for helium diffusion along vacancy chain is significantly reduced to 0.61 eV, suggesting such O vacancy chain would provide the fast diffusion path for helium to escape from α-Al2O3 due to its large positive formation energy in the bulk.

Ab initio calculations have been performed to study the formation and migration energies of helium atoms and the stability of helium-vacancy clusters in a Y2O3 crystal. The calculated formation energies show that a helium atom is preferred to occupy an yttrium vacancy site with a large volume and low electron density. The migration energy of the helium atom by an interstitial mechanism is 0.31 eV. Calculations of the binding energies of an extra helium atom to the helium-vacancy clusters vary with the number of helium atoms in the clusters with a typical value of 0.4–0.7 eV. This turns negative when the He atoms reach saturation; that indicates that vacancy clusters can attract a limited number of helium atoms to form small stable helium-vacancy clusters. Our calculations suggest that the use of Y2O3 in oxide dispersion strengthened ferritic steels may reduce He gas bubble formation as it may act as sink for trapping helium atoms.