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First-principles theory is applied to identify the structure of γ-Al 2 O 3 first. Then, hydrogen dissolution and diffusion behavior was further studied to reveal the reason that permeation reduction factor (PRF) of γ-Al 2 O 3 is lower than that of α-Al 2 O 3. Our calculations show that the formation energy for Al vacancy at the octahedral interstitial site (V Al − OIS − 3) is lower than that at the tetrahedral interstitial site (V Al − TIS − 3), and are far lower than those of other defects in both defective spinel and non-spinel γ-Al 2 O 3. Thus, the stability of V Al − OIS − 3 is higher than that of V Al − TIS − 3 in both Al-rich and O-rich environments. However, when hydrogen atoms are introduced into γ-Al 2 O 3 , the stability of [V Al-TIS -H]−2 is higher than that of [V Al-OIS -H]−2 in the defective spinel γ-Al 2 O 3 structure, while the opposite is true for the non-spinel γ-Al 2 O 3 structure. The vibrational frequencies for OH− in [V Al-TIS -H]−2 and [V Al-OIS -H]−2 for defective γ-Al 2 O 3 are calculated to be 3608 cm−1 and 3374 cm−1, respectively, which is in excellent agreement with the infrared (IR) absorption peaks observed at ∼3500 and ∼3300 cm−1. The defective spinel model is more suitable for describing the γ-Al 2 O 3 structure. In defective spinel γ-Al 2 O 3 , there are many native Al vacancies, which are arranged in a straight line along the [ 2 1 ¯ 1 ¯ 0 ] direction. The migration barrier for H diffusion along these native Al vacancies is so low that these Al vacancies can provide a rapid diffusion channel for H. Thus, the permeability of H in γ-Al 2 O 3 is much higher than that in α-Al 2 O 3 leading to a lower permeation reduction factor (PRF). Our results can provide not only a sound theoretical explanation for the low PRF of γ-Al 2 O 3 but also a direction to improve the efficiency in preventing H permeation through FeAl/Al 2 O 3 tritium permeation barriers (TPBs). [ABSTRACT FROM AUTHOR]

To evaluate the influence of He ions irradiation on the deuterium permeation and retention behavior in RAFM steels, samples made of the CLF-1 steel was irradiated with 3.5 MeV He ions. Gas driven permeation experiments were performed, and the permeability of virgin sample and pre-irradiated sample were obtained and compared. In order to characterize the effect of He ions irradiation on the deuterium retention behavior, deuterium gas exposure was carried out at 623 K, followed by thermal desorption spectra experiments. The total deuterium retention of the CLF-1 steel increased owing to He ions implantation, which could be attributed to the increase in trapping site for deuterium by the He pre-irradiation. [ABSTRACT FROM AUTHOR]

In fusion reactors, tritium permeation barrier (TPB) technology is one of the key scientific technologies. α-Al 2 O 3 has been considered an ideal candidate material for TPBs. In this work, a series of first-principles calculations have been performed to investigate the dissolution, clustering and diffusion behavior of hydrogen (H) in bulk α-Al 2 O 3. The calculation results show that the most energetically stable form of hydrogen in a perfect α-Al 2 O 3 crystal under H 2 gas annealing treatment is the H 2 molecule. This can also be confirmed by the electron localization function results. The attraction between two H atoms located in first and second nearest octahedral interstitial sites (OISs) is so strong that if multiple H atoms are dissolved in α-Al 2 O 3 , these atoms can migrate toward their adjacent H atoms and form clusters, which will prevent further diffusion of H. The most stable configuration of H cluster in α-Al 2 O 3 is 2H i , with the smallest formation energy and the largest average binding energy. The formation energy and binding energy are similar to those of the gaseous H 2 molecule. We have derived the temperature-dependent diffusivity of the H 2 molecule in α-Al 2 O 3 as D (T) = (3.65 × 10 − 7 m 2 / s) e x p (− 2.27 e V / K T) , which is in good agreement with the experimental values. In addition, both the dissolution energy and migration barrier of the H 2 molecule are so high that dissolution and diffusion of the H 2 molecule in α-Al 2 O 3 are very difficult, resulting in low hydrogen permeability. [ABSTRACT FROM AUTHOR]

Our previous study has shown that an effective tritium permeation barrier (TPB) with Al 2 O 3 layer found could be obtained by oxidization of a Fe–Cr–Al ferritic steel. In this study, irradiation effects on deuterium permeation behavior through oxidized Fe–Cr–Al ferritic steel (OFFS) have been investigated by Au ions irradiation followed by deuterium gas driven permeation (GDP) experiments. The deuterium permeability of the irradiated and original OFFS samples has been obtained and compared. Oxide layer has been characterized by X-ray photoelectron spectroscopy (XPS) experiment and scanning electron microscopy (SEM) experiment. The defects in the oxide layer with and without Au ions irradiation have been characterized by Doppler broadening spectrometry of positron annihilation (DBS-PA) experiments. The deuterium permeation behavior of OFFS changed owing to the Au ions irradiation, which could be attributed to the increased density of vacancy-type defects. • Oxidized Fe–Cr–Al ferritic steel (OFFS) has been irradiated by Au ions. • The defects in OFFS have been characterized by DBS-PA experiments. • D 2 GDP experiments have been performed for OFFS. • Vacancy-type defects have influence on D 2 permeation behavior of OFFS. [ABSTRACT FROM AUTHOR]

Owing to its excellent properties, high-entropy alloys (HEAs) have been regarded as a kind of promising candidate structural material for nuclear devices. For the safety concern, it is vital to figure out the compatibility of hydrogen isotopes with the HEAs. In this work, the hydrogen isotope permeation and retention behavior of a representative HEA, CoCrFeMnNi, has been mainly checked by a gas-driven permeation device and a thermal desorption spectra device. The hydrogen isotope permeation parameters have been obtained, which are quite similar to those of the 316L austenitic steels. The hydrogen isotope retention behavior has been compared with that for a reduced activation ferritic/martensitic steel, and the relatively high hydrogen isotope inventory in HEA has been explained by crystalline structure and high density of hydrogen trapping site. [ABSTRACT FROM AUTHOR]

Reduced activation ferritic/martensitic (RAFM) steels are the primary candidate structural materials for the blanket in future fusion power plants. In the recent years, a novel 9–12% Cr modified F/M steel named SIMP steel has been developed. The deuterium permeation behavior of the SIMP steel with and without oxide layer has been evaluated using a gas driven permeation (GDP) device. The permeability of original and oxidized SIMP steel has been derived and compared. In order to characterize the oxide layer, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) experiments have been carried out. GDP results show that the SIMP steel has similar deuterium permeability with the CLF-1 steel. The deuterium permeability of the oxidized SIMP steel is lower than that of the original SIMP steel. Heat treatment during the oxidization process has limited influence on the deuterium permeability of the bare SIMP steel. The cross-section SEM pictures present that with the increase of the oxidation time, the thickness of the oxide layer is increased. The oxide layers are observed to be porous. The results of XRD and EDS show that the oxide layer mainly consists of chromium oxide and accumulation of chromium can be detected in the surface region. The formation of the chromium oxide on the surface of the SIMP steel could be the reason of the decrease of the deuterium permeability of the oxidized SIMP steel. • The deuterium permeation behavior of the SIMP steel with and without oxide layer was first investigated. • The microstructural change has been characterized by SEM, EDS and XRD. • The deuterium permeability of the oxidized SIMP steel was 4–8 times lower than that of original SIMP steel. • The oxide layers were detected to be porous, which might be the reason why the hydrogen permeability is reduced slightly. [ABSTRACT FROM AUTHOR]

The permeation behavior of creep-resistant, Al 2 O 3 -forming HTUPS austenitic stainless steels was studied using a gas driven permeation (GDP) device. The steel samples were first thermal oxidized at air condition, followed by GDP experiments. The permeability and diffusion coefficients of oxidized samples and bare 316L steels were derived and compared. In order to characterize the oxide layer, X-ray photoelectron spectroscopy was performed. An oxide layer with a thickness of 200 nm which mainly consists of Al 2 O 3 was detected. [ABSTRACT FROM AUTHOR]

Permeation behavior of deuterium (D) through various tungsten (W) materials, including rolled, annealed, recrystallized W and ZrC/La 2 O 3 -dispersion strengthened W, has been studied. Experiments were performed using a gas-driven permeation facility in the temperature range of 700–1000 K. The permeability of D was not sensitive to the dislocations/vacancies or ZrC/La 2 O 3 phases in W, and the measured permeation values are comparable to Frauenfelder and Zahkarov’s data. The diffusivity of D, however, is microstructure dependent. The higher the density of defects was, the lower the effective diffusivity was measured. These results imply that dislocations/vacancies or small amounts of ZrC/La 2 O 3 phases in W will not influence the hydrogen isotopes steady state permeation flux through the first wall. [ABSTRACT FROM AUTHOR]

To evaluate the capability of Fe Cr Al ferritic steels as tritium permeation barrier in fusion systems, the oxidation behavior together with the permeation behavior of a Fe Cr Al steel was investigated. Gas driven permeation experiments were performed. The permeability of the oxidized Fe Cr Al steel was obtained and a reduced activation ferritic/martensitic steel CLF-1 was used as a comparison. In order to characterize the oxide layer, SEM, XPS, TEM, HRTEM were used. Al 2 O 3 was detected in the oxide film by XPS, and HRTEM showed that Al 2 O 3 in the α phase was found. The formation of α-Al 2 O 3 layer at a relatively low temperature may result from the formation of Cr 2 O 3 nuclei. [ABSTRACT FROM AUTHOR]

The influence of the transmutation element rhenium (Re) content with 3 and 25 wt.% on deuterium (D) permeation in tungsten (W) was investigated. It was found that the addition of Re increased D diffusion coefficient and decreased D permeability, and the D diffusion coefficient of W-3%Re was approximate to that of W-25%Re while the D permeability declined with the increase of Re content. The D retention behavior in the W-Re alloys have been studied after D plasmas exposure employing the Material and Plasma Evaluation System (MAPES) in Experimental Advanced Superconducting Tokamak (EAST). As for the higher D solution energy in W-Re alloys, the total D inventory in W was significantly decreased by Re addition. [ABSTRACT FROM AUTHOR]