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This paper reviews the control and the application of ultrahigh hydrogen flux in materials for fusion reactors and future hydrogen societies. Ultrahigh hydrogen flux can be efficiently formed by the combination of hydrogen plasma exposure and the surface modification method, similar to super-permeation. The paper discusses the possibility of the fabrication of oversaturated hydrogen storage materials and the effective tritium removal from the components using the ultrahigh hydrogen flux.

The evolution of interstitial dislocation loops in V-4Cr-4Ti during heavy ion and neutron irradiation was investigated in comparison with that during electron irradiation at temperature ranging from 407 K to 673 K. Temperature and damage rate dependence of the loop number density by heavy ion and neutron irradiations agreed well with those by electron irradiation obeying Sink and Recombination Dominant kinetics at low and high temperature, respectively. Heavy ion and neutron irradiations induced higher loop number density than that of electron irradiation at 563 - 673 K. The difference may be attributed to cascade-enhanced vacancy loop formation., source:https://doi.org/10.1585/pfr.11.2405007, identifier:0000-0001-5598-1895

Hydrogen isotopes plasma-driven permeation (PDP) through F82H coated with two different types of tungsten coatings, i.e., sputter-deposited tungsten (SP-W) and vacuum plasma-sprayed tungsten (VPS-W) has been studied in the temperature range of 300 - 550 °C. It has been found that hydrogen isotopes PDP fluxes through VPS-W coated F82H are reduced compared to that through bare F82H. However, the PDP fluxes through SP-W coated F82H are enhanced compared to bare F82H. Reduced or enhanced PDP fluxes are related to the different microstructure of tungsten coatings and its surface recombination characteristics., source:https://doi.org/10.1585/pfr.12.1205009

The effects of oxygen pick-up in an irradiation environment in a vacuum chamber during ion- and neutron-irradiation of V-4Cr-4Ti alloys were studied. The density and size of titanium oxides in the alloys were found to drastically increase because of the oxygen pick-up, especially for cases of higher irradiation dose and specimen temperature. Using Zr foil as a diffusion barrier and doping the V-4Cr-4Ti alloys with Y can be considered as effective techniques for reducing the reaction of Ti with C, O, and N to form Ti(C,O,N) because of oxygen-pick up from irradiation environment., source:https://doi.org/10.1585/pfr.12.2405011

Release behaviors of tritium from molten FLiNaBe (LiF–NaF–BeF2) have been examined in a series of low flux neutron irradiation experiments with an AmBe neutron source at the OKTAVIAN facility of Osaka University. Tritium released from FLiNaBe is swept by He and Ar gases, and recovered by water bubblers. The recovery rate of tritium released from 300 cm3 of FLiNaBe was 58.0 mBq/h in a steady state, and it was close to the tritium production rate of 58.0 mBq/h calculated by the MCNP6 code. The values of the overall mass transfer coefficients for tritium release from FLiNaBe were close to those for FLiNaK (LiF–NaF–KF) at 773 K. The influence of the diffusivity and the solubility of tritium on the overall mass transfer coefficients has been examined on molten FLiNaBe., source:https://doi.org/10.1585/pfr.14.1405044, identifier:0000-0001-5341-5814

Four V-Ta-4Cr-4Ti quaternary alloys containing different quantities of Ta were investigated to determine the effect of Ta content on the Charpy impact properties. Five button-shaped ingots of the V-4Cr-4Ti ternary alloy and V-xTa-4Cr-4Ti quaternary alloys (x = 3, 9, 15, and 22 wt.%) were fabricated on a laboratory scale by using non-consumable arc-melting in an argon atmosphere. Charpy impact tests were conducted at temperatures ranging from 77 K to 293 K using an instrumented impact tester. Both the upper shelf energy and the ductile–brittle transition temperature increased with increasing Ta content. The addition of 3 wt.% Ta resulted in solid solution strengthening without any degradation of the Charpy impact properties. Thus, the addition of 3 wt.% Ta (V-3Ta-4Cr-4Ti) is an appropriate amount to use in blanket structural materials for nuclear fusion reactors. The spectra of TEM-EDS for V-3Ta-4Cr-4Ti quaternary alloy indicate that there is no significant enrichment of Ta in the matrix as compared with that in the precipitate. However, thermal aging may result in the formation of the Laves phase, causing the degradation of Charpy impact properties. The characterization of precipitates, thermal aging, and creep tests of the V-3Ta-4Cr-4Ti quaternary alloy need to be investigated to determine the optimum Ta content., source:https://doi.org/10.1016/j.nme.2022.101198, identifier:0000-0001-6564-8922

Reduction of interstitial impurities such as nitrogen (N) and oxygen (O) improves the mechanical properties of V-4Cr-4Ti alloys. Yttrium (Y) addition effectively reduces O content by Y2O3 slag-out on the melting ingot surface. The effects of Y addition on mechanical properties were investigated for V-4Cr-4Ti with N ranging from 0.009 to 0.29 mass% and O ranging from 0.009 to 0.36 mass%. The increase in yield stress (YS) and ultimate tensile stress (UTS) for vanadium alloys was saturated above 0.1 mass% in O content, because Ti precipitates increased with increasing O content regardless of Y addition. Y addition had little effect on YS and UTS of V-4Cr-4Ti alloys at room temperature (RT). However, Y addition improved impact properties of alloys highly doped with O. Y addition did not suppress hardening due to O doping but did increase deformation for crack initiation., source:https://doi.org/10.1585/pfr.8.1405166, identifier:0000-0001-6564-8922

Various V-Ta-4Cr-4Ti quaternary alloys containing different amounts of Ta were investigated to determine the effect of Ta concentration on their tensile properties. Six button-shaped ingots of V-xTa-4Cr-4Ti alloys (x = 4, 8, 15, 22, 24, and 35 wt.%) were fabricated on a laboratory scale by using non-consumable arc-melting in argon atmosphere. The sheet specimens for all the V-Ta-4Cr-4Ti alloys examined herein were obtained by cold-rolling; hot-rolling or intermediate annealing was not required. Although the examined alloys were fabricated on a laboratory scale, the high-Ta alloys, unlike the high-Cr alloys, did not experience crack formation in the cold rolling process. It is possible that V-4Cr-4Ti alloys adopt large amount of Ta and its strengthening effect without negative impact on rolling fabricability. Tensile strength tended to increase with increasing Ta content at both room temperature and high temperatures of 973 K and 1073 K, which can be attributed to the solid solution strengthening by Ta. Thus, addition of Ta to V-4Cr-4Ti alloys can improve their strength without decreasing their rolling fabricabilities. However, an alloy containing excess Ta (V-35Ta-4Cr-4Ti) showed a loss of ductility and a brittle fracture mode due to the formation of a large amount of friable Laves phase. Therefore, it is necessary to limit the amount of Ta to prevent the formation of the Laves phase., source:https://doi.org/10.1016/j.fusengdes.2020.112191, identifier:0000-0001-6564-8922

In order to improve the performance of vanadium alloys for fusion reactors, yttrium (Y) was added to reduce the interstitial O in the matrix by enhanced precipitation with Y. Effect of Y on interstitial C, N and O, however, remains to be investigated since they affect mechanical and fracture properties for vanadium alloys by pinning dislocations, such as dynamic strain aging (DSA). In this study, tensile tests were carried out on annealed V–4Cr–4Ti and V–4Cr–4Ti–Y alloys from 473 to 1073 K at strain rates ranging from 6.67 × 10−5 to 6.67 × 10−1 s−1 to investigate the performance of DSA. In the case of high-purity alloys, DSA regime was narrowed due to Y addition and the reduction in O content. In the case of O doped V–4Cr–4Ti alloys, DSA regime was also narrowed. This may be because the enhanced Ti–O precipitation reduced the O level in the matrix. Also, coarse precipitates (<500 nm) were observed in O doped V–4Cr–4Ti–Y alloy. Y might enhance the coarsening of Ti-precipitates. From activation energies for DSA, the diffusion of C and O is considered to induce the observed DSA. Y does not influence the diffusion of C and O, and might enhance the nucleation to form coarse precipitates., source:https://doi.org/10.1016/j.jnucmat.2013.03.091, identifier:0000-0001-6564-8922

In order to improve irradiation embrittlement of vanadium alloys for fusion reactors, yttrium (Y) has been added reducing the interstitial oxygen impurity. However Y addition can also degrade high-temperature strength, because Y could scavenge oxygen in solid solution, which is a strong hardening agent in vanadium alloys. In this study, the effect of Y addition and oxygen level on the mechanical properties was investigated from the view points of both the high-temperature strength and low temperature ductility. Y addition was suggested to moderate the hardening and embrittlement induced by oxygen impurity sustaining the high-temperature strength within an acceptable level., source:To cite this article: Takeshi Miyazawa, Takuya Nagasaka, Yoshimitsu Hishinuma, Takeo Muroga & Yanfen Li (2011) Moderation of Negative Oxygen Effects by Small Yttrium Addition to Low Activation Vanadium Alloys, Fusion Science and Technology, 60:1, 407-411, DOI: 10.13182/ FST11-A12390, source:https://doi.org/10.13182/FST11-A12390, identifier:0000-0001-6564-8922

Bead-on-plate welds were produced on the 4 mm-thick V-4Cr-4Ti alloy (NIFS-HEAT-2), using a 2.0 kW YAG laser. The post-weld heat treatments (PWHT) were carried out in various conditions. Microstructures, Vickers hardness and Charpy impact properties were obtained for the weld metal after the PWHT. After PWHT for one hour, the hardness increased and after the peak declined with temperature. At 873 K, the hardness increased and after the peak declined with the time of PWHT. Microstructural observation showed that high density of fine precipitates formed homogeneously when the hardness increased, but the precipitate distribution changed into heterogeneous forming islands of developed precipitate aggregates, coincident with decrease in hardness and recovery of impact properties. Optical microscope observations suggested that a cellular structure of precipitate aggregate region was formed by PWHT. Microchemical analysis showed that Ti was enriched in the precipitate aggregate region. Therefore the areal oscillation of Ti concentration with cellular structures formed by melting and resolidification during the welding resulted in the heterogeneous precipitation by the following PWHT. The precipitation in the Ti-rich area purified the matrix of the weld metal and induced the recovery of hardening and impact property degradation. Optimum PWHT conditions were discussed according to the present results., source:https://doi.org/10.1585/pfr.10.1405092, identifier:0000-0001-5598-1895

Dissimilar joints between 9Cr-ODS and JLF-1 were fabricated by hot isostatic pressing (HIP) and by electron beam welding (EBW), respectively. Compared to the HIP at 1000 °C, HIP at higher temperatures of 1050 °C and 1100 °C is effective to improve the joining strength of the joints. All the as-HIPed joints fractured at the interface during tensile tests. 1050 °C-HIP showed the best joining strength and reduction of area. Post-weld heat treatment (PWHT) with normalization and tempering (N&T) could further improve the joining properties of the HIPed joints. The joints fractured outside the interface at the JLF-1 base metals. EBW showed better weld-ability than HIP, because the joint made by EBW did not fracture at the weld metal during tensile tests, but always fractured at JLF-1 side. However, the properties of the HIPed joints were improved after PWHT with N&T, and were comparable to that made by EBW., source:https://doi.org/10.1585/pfr.10.3405015

The key to improving the heat load of vacuum plasma sprayed tungsten coatings on low activation ferritic steel maintained at low temperatures is elimination of stratified low-density layers with many large pores, in which thermal cracks propagate preferentially. The low-density layers are formed owing to the deposition of large solidified tungsten particles, which remain mainly at the periphery of the spray stream. In this study, by shading this periphery, partially homogeneous tungsten coatings without large pores were successfully obtained. The coatings are expected to show good heat load, which is feasible for nuclear fusion applications., source:https://doi.org/10.1585/pfr.8.1405111

The key to improving the heat load of vacuum plasma sprayed tungsten coatings on low activation ferritic steel maintained at low temperatures is elimination of stratified low-density layers with many large pores, in which thermal cracks propagate preferentially. The low-density layers are formed owing to the deposition of large solidified tungsten particles, which remain mainly at the periphery of the spray stream. In this study, by shading this periphery, partially homogeneous tungsten coatings without large pores were successfully obtained. The coatings are expected to show good heat load, which is feasible for nuclear fusion applications.