Effect of Argon Ion Sputtering of Surface on Hydrogen Permeation through Vanadium, (II) Effect of Sputtering of Both Side Surfaces

As part of studies on plasma-wall interactions of fusion reactors, the effect of Ar ion sputtering of both the upstream side and the downstream side surfaces of a V coupon upon its H₂ permeability has been studied. The H₂ permeability measuring apparatus has been modified to install another ion gun for the use in sputtering the downstream side specimen surface. The H₂ permeation rates were measured at 673K by changing the H₂ pressure and sputtering mode. The downstream side sputtering has been observed to enhance the H₂ permeability, though its degree was smaller than that due to the upstream side sputtering. The both side sputtering resulted in the largest H₂ permeability value ever obtained for V. The rate of H₂ permeation through V seemed to be determined by the surface processes including the downstream side rather than the bulk diffusion even after the both side sputtering. Based on AES measurements, the enhancement of H₂ permeability caused by sputtering was attributed to the diminishing of the surface O impurity.     

Permeability of hydrogen and deuterium of Hastelloy XR

Permeation of hydrogen isotope through a high-temperature alloy used as heat exchanger and steam reformer pipes is an important problem in the hydrogen production system connected to be a high-temperature engineering test reactor (HTTR). An experiment of hydrogen (H₂) and deuterium (D₂) permeation was performed to obtain permeability of H₂ and D₂ of Hastelloy XR, which is adopted as heat transfer pipe of an intermediate heat exchanger of the HTTR. Permeability of H₂ and D₂ of Hastelloy XR were obtained as follows. The activation energy E₀ and pre-exponential factor F₀ of the permeability of H₂ were E₀=67.2±1.2 kJ mol⁻¹ and F₀=(1.0±0.2)×10⁻⁸ m³(STP) m⁻¹ s⁻¹ Pa^−0.5, respectively, in the pipe temperature ranging from 843 K (570 °C) to 1093 K (820 °C). E₀ and F₀ of the permeability of D₂ were respectively E₀=76.6±0.5 kJ mol⁻¹ and F₀=(2.5±0.3)×10⁻⁸ m³(STP) m⁻¹ s⁻¹ Pa^−0.5 in the pipe temperature ranging from 943 K (670 °C) to 1093 K (820 °C).     

Hydrogen and Deuterium Transport through Type 304 Stainless Steel at Elevated Temperatures

The permeation time-lag method have been used to determine the permeabilities, diffusion coefficients and solubilities of hydrogen and deuterium in type 304 stainless steel of three kinds of surface treated specimens; with oxide film, reduced by H₂ gas and Pd coated. For the specimen with a thin oxide film the permeability increased abruptly at the temperature higher than 1,050 K owing to reduction of the oxide film by H₂ gas introduced. The permeability and diffusion coefficient for hydrogen-reduced specimens agreed with those for Pd-coated specimens showing the data of bulk diffusion limited. The isotope effects for permeability Φ_H/Φ_D, diffusion coefficient D _H/D _D and solubility were about 1.4, 1.2 and 1.1, respectively. From these values θ(=hν/k)=1,530±50K and θ′(=hν/k)=2,740±20K were obtained by the quantum effect of a harmonic approximation.     

Deuterium permeation behavior for damaged tungsten by ion implantation

The deuterium (D) permeation behaviors for ion-damaged tungsten (W) by 3 keV D₂⁺ and 10 keV C⁺ were studied. The D permeability was obtained for un-damaged W at various temperatures. For both D₂⁺ and C⁺ implanted W, the permeability was clearly reduced. But, for the D₂⁺ implanted W, the permeability was recovered by heating at 1173 K and it was almost consistent with that for un-damaged W. In the case of C⁺ implanted W, the permeability was not recovered even if the sample was heated at 1173 K, indicating that the existence of carbon would prevent the recovery of permeation path in W. In addition, transmission electron microscope (TEM) observation showed the voids were grown by heating at 1173 K and not removed, showing the existence of damages would not largely influence on the hydrogen permeation behavior in W in the present study.     

Photo-Neutron Production in Heliotron-E

Photo-neutron emission in H₂ and He discharges was observed in the initial ohmic heating experiments of the Heliotron-E. Typical total neutron yield was 10⁹ neutrons per pulse under high level of runaway electrons (≧10 MeV). Neutron flux was localized near the limiters. Energy spectrum of neutrons was continuous up to about 2 MeV. The radioactive nuclides in the limiters and the vacuum chamber irradiated by runaway electrons showed that ⁵⁸Ni(γ, n) ⁵⁷Ni and ⁵³Cr(γ, n)⁵¹Cr reactions had occurred, proving that the photo-disintegration process was the source of neutron flux.     

Hydrogen backscattering from TiN,TiC and TiB2

Particle reflection coefficients, R_n, for H⁺ and H₂⁺ bombarding TiN, TiC and TiB₂ targets were determined by measurement of the energy distributions of neutral and charged particles backscattered at 135°. The values of R_n were determined for incident energies between 2.5 and 10 keV and were found to decrease with increasing energy. The reflected fractions were also found to decrease in going from TiN to TiC to TiB₂ at any given incident energy. The angular distribution of particles backscattered from TiC bombarded by 10 keV H₂⁺ was measured and found to agree well with a cosine distribution.     

The influence of relative humidity on iron corrosion under proton irradiation

With regard to the storage for high-level radioactive waste and the reversible period of a geological repository, the influence of proton irradiation on the indoor atmospheric corrosion of iron has been investigated in relation to the relative humidity (RH) in the atmosphere. Irradiation experiments were performed using a 3-MeV extracted proton beam. Relative humidity varies from 0% to 85%. Before and after each irradiation, the surfaces of the sample were characterised by Rutherford backscattering spectrometry in order to determine oxygen concentrations in the metal. The maximum oxidation rate was observed for 45% RH in air under proton irradiation and was compared with literature data without irradiation where the maximum oxidation rate was observed at 95% RH. The experimental results are discussed on the basis of the Langmuir-Hinshelwood (LH) model: they are explained by the contrast between the adsorption of O₂ and H₂O species on the active cathodic sites of the iron surface and by the formation of H⁺(H₂O)_n.     

Analysis of Tritium Behavior in Very High Temperature Gas-Cooled Reactor Coupled with Thermochemical Iodine-Sulfur Process for Hydrogen Production

The tritium concentration in the hydrogen product in Japan's future very high temperature gas-cooled reactor (VHTR) system coupled with a thermochemical water-splitting iodine-sulfur (IS) process (VHTRIS system), named GTHTR300C, was estimated by numerical analysis. The tritium concentration in the hydrogen product significantly depended on undetermined parameters, i.e., the permeabilities of a SO₃ decomposer and a H₂SO₄vaporizer made of SiC. Thus, the estimated tritium concentration in the hydrogen product for the conservative analytical condition ranged from 3.4 × 10^?3 Bq/cm³ at STP (38 Bq/g-H₂) to 0.18 Bq/cm³ at STP (2,000 Bq/g-H₂). By considering the tritium retained by core graphite and the reduction in permeation rate by an oxide film on the heat transfer tube of the IHX and the HI decomposer, the tritium concentration in the hydrogen product decreased to the range from 3.3 × 10^?5 Bq/cm³ at STP (0.36 Bq/g-H₂) to 5.6 × 10^?3 Bq/cm³ at STP (63 Bq/g-H₂), which were smaller than those for the conservative analytical condition by factors of about 3.2 × 10^?2 and 9.6 × 10^?3, respectively. The effectof the helium flow rate in the helium purification system on the tritium concentration in the hydrogen product was also evaluated.     

The effect of irradiation and post-irradiation annealing on the yield stress and microstructure of vanadium-carbon alloys

Vanadium and vanadium-carbon alloys containing 0.15, 0.3 and 1 at% carbon were irradiated in JMTR with fast neutrons (E_n > 1 MeV) at 773 K to a dose of 5 × 10²⁴n/m². Tensile test and microstructural observations were carried out after irradiation and post-irradiation annealing. All of the. specimens showed radiation hardening. The irradiation produced voids, dislocations and radiation-induced quasi-carbides, which were formed by the agglomeration of vacancies and carbon atoms. The radiation anneal hardening in the alloys occurred at 873 K. The void number densities in the alloys had a peak at 873 K while the quasi-carbides decomposed at the same temperature. Therefore, invisible voids existing in the as-irradiated condition would grow by absorbing the vacancies, which were released in the process of decomposition of the quasicarbides during annealing, and the increase of the visible voids would effectively contribute to the radiation anneal hardening of these alloys.     

Fabrication and characterization of uranium-thorium-zirconium hydrides

Two uranium-thorium-zirconium hydrides, (UTh₄Zr₁₀)H_1.9 and (U₄Th₂Zr₉)H_1.5, have been fabricated and characterized. Fabrication involved arc melting of the constituent pure metals to form homogenous alloys, followed by hydriding at elevated temperatures in a hydrogen gas environment. The compounds were characterized by X-ray powder diffractometry as well as scanning and transmission electron microscopy. These methods revealed a multi-phase mixture of δ-zirconium hydride (ZrH_1.6+x), thorium-zirconium hydride (ThZr₂H_7−x), and uranium metal. The elastic modulus was mapped across the microstructure using nanoscale dynamic stiffness mapping. The elastic modulus of ThZr₂H_7−x phase is found to be 172 GPa.     

Hydrogen diffusive transport parameters in W coating for fusion applications

Combined Magnetron Sputtering and Ion Implantation (CMSII) technology was used for W coating of carbon based materials (Carbon Fibre Composite - CFC and fine grain graphite) for the first wall in fusion devices. The coating thickness was 10-15 μm or 20-25 μm depending on the position of the tile at the wall. While such coatings successfully passed the demanding thermo-mechanical tests, not much is known about its hydrogen interaction. The latter is particularly important for the assessment of tritium retention. Due to the low hydrogen diffusivity and very small volume of W in the coated layer, the gaseous hydrogen permeation measurement at 400 °C was selected for the experimental technique, where increasing & decreasing transient and steady state permeation flux was monitored. Problems that could arise with the CFC membrane sealing were overcome by deposition of the identical W layer on the 0.5 mm Eurofer substrate. Two such membranes were investigated. Obtained hydrogen permeability in tungsten layer (∼10⁻¹³ mol H₂/m s Pa^0.5) is comparable to the upper range of published data. Measured diffusivity (∼10⁻¹⁴ m²/s) is several orders of magnitude lower compared to the average of published data for tungsten, while the measured solubility (∼1 mol H₂/m³ Pa^0.5) is several orders of magnitude higher. The explanation is given in terms of hydrogen trapping that has significant impact on hydrogen migration.     

Experimental cross sections for two-electron capture into nitrogen autoionising states in Nq+ (q = 6, 7) on He and H2 collisions at 10.5q keV

Singly differential cross sections for two-electron capture into autoionising states (nl, n'l') with n = 2, 3, 4 and n′≥ in N^q+ (q = 6, 7) on He and H₂ collisions have been measured at 10.5q keV collision energy and an observation angle θ_lab =11.6°Total cross sections are estimated assuming isotropic angular distributions.     

Charge transfer and delocalization studies from Kβ-to-Kα intensity ratios in CoxCu1−x alloys

Kβ-to-Kα X-ray intensity ratios of Co and Cu have been measured in pure metals and in alloys of Co_xCu_1−x (x = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2) following excitation by 22.69 keV X-rays from a ¹⁰⁹Cd radioactive point source. The valence-electronic configurations of these metals were determined by corporation of measured Kβ-to-Kα X-ray intensity ratios with the results of multiconfiguration Dirac–Fock (MCDF) calculation for various valence-electronic configurations. Valance electronic configurations of Co and Cu in alloys indicate significant differences with respect to the pure metals. Our analysis indicates that these differences arise from delocalization and/or charge transfer phenomena in alloys. Namely the observed change of the valence-electronic configurations of metals in alloys can be explained with the transfer of 3d electrons from one element to the other element and/or the rearrangement of electrons between 3d and 4s, 4p states of individual metal atoms.     

Hydrogen isotope permeation from cooling water through various metal piping

In order to investigate the behavior of hydrogen isotope on the water–metal boundary, deuterium permeation experiments from heavy water vessel through various metal piping, such as pure iron (Fe), nickel (Ni), stainless steel (SS304), and pure iron with 10 μm gold plating, were performed at 573 K and at 15 MPa. During the experiment, surfaces of metal piping except gold plating one were oxidized at the heavy water boundary and then deuterium would generate by the oxidation reactions. This deuterium could be detected by mass spectrometer, which monitored the inside gases of the piping under continuous evacuation. The result showed clearly that the deuterium permeated through Fe, Ni, and SS304 piping was detected as mainly deuterium gas (D₂) under continuous evacuation, though that through gold plating one could not be detected effectively. The D₂ permeation rate through Fe, Ni, and SS304 piping reached equilibrium conditions with oxide generation at D₂O–metal boundary, although concluding the transfer mechanism will require further testing and modeling activities.     

The rates of thermal decomposition of LiOH(s), LiOD(s) and LiOT(s)

Kinetic studies on the thermal decomposition reactions, 2LiOH(s) → Li₂O(s) + H₂O(g), 2LiOD(s) → Li₂O(s) + D₂O(g), and LiOH(s) + LiOT(s) → Li₂O(s) + HTO(g), have been carried out with mass spectrometric and radiometric methods over the temperature range 530–690 K. Those reaction rates were found to be of first order in the quantity of released water. The rate-constants, k, in s^?1, were: k_H2O = 1.8 × 10⁸ exp(29 500/RT), k_D2O = 1.7 × 10⁸ exp(29 000/RT), and k_HTO = 1.6 × 10⁷ exp(30 700/RT), respectively. The apparent activation energy obtained for the thermal decomposition of LiOH(s), E_a = 29.5 ± 1.1 kcal/mol, coincided with a literature value of the enthalpy of reaction, ΔH°₆₀₀^° = 29.8 ± 1.0 kcal/mol.     

Calculation of fine-structure energy levels and autoionizing widths for the magnesium-like ions Ti XI and Fe XV

We have calculated highly excited fine-structure energy levels and their autoionizing widths for the 3pns ³P₁(n=9-33), 3pns ¹P₁(n=9-27), 3pnd ³D₁(n=9-35), 3pnd ³P₁(n=8-26), 3pnd ¹P₁(n=8-26), 3dnp³D₁(n=6,8-29), 3dnp³P₁(n=6,8-29), 3dnp ¹P₁(n=6,8-28), 3dnf ³D₁(n=7-28), 3dnf ³P₁(n=7-27), and 3dnf ¹P₁(n=7-27) states of the magnesium-like ion Ti XI and for the 3pns ³P₁(n=10-35), 3pns ¹P₁(n=10-25), 3pnd ³D₁(n=10-35),3pnd ³P₁(n=10-25),3pnd ¹P₁(n=10-24),3dnp ³D₁(n=7,9-31),3dnp ³P₁(n=7,9-31),3dnp ¹P₁(n=7,9-28),3dnf ³D₁(n=9-30),3dnf ³P₁(n=9-28), and 3dnf ¹P₁(n=9-28) states of the magnesium-like ion Fe XV. The calculations are based on the relativistic Breit-Pauli R-matrix approximation combined with the QB method [L. Quigley, K. Berrington, J. Pelan, Comput. Phys. Commun. 144 (1998) 225]. We report many previously unpublished energy values and autoionizing widths for these magnesium-like ions.     

Impact of Material Configuration Behind First Wall on Helium Formation in In-Vessel Components of Fusion Reactor

The results of neutron transport calculations of the He formation based on the JENDL gas-production cross section file are discussed for some metals and alloys, namely ²⁷A1, Ti, ⁵¹V, Cr, ⁵⁵Mn, Fe, Ni, Zr, Mo, austenitic stainless steel (Ti modified 316 SS: PCA), Ni-base alloy (Inconel 625), ferritic steel (Fe-11Cr-1Mo: HT-9), Ti-base alloy (Ti-6A1-4V) and V-base alloy (V-5Cr-5Ti). Impacts of the two shields having the steel-rich and the H₂O-rich compositions and the two blankets having the Li₂O/Be-base and the liquid Li/Be-base compositions on the He formation rate in the above-mentioned metals and alloys are discussed. The relation between the He formation rate and the fast neutron flux (14.1 MeV>E>0.1 MeV) is investigated. The decrease of He formation at any distance Δ from the first wall more than Δ_as, the distance where the shape of neutron spectrum reaches its asymptotic form, is modelled by the simple formula based on the exponential dependence, as those reported so far for the fast neutron flux and the displacement damage rate.     

Thermal annealing behavior of hydrogen and surface topography of H2+ ion implanted tungsten

Tungsten (W) has been proposed as a plasma-facing material in fusion reactors due to its outstanding properties. Degradation of the material properties is expected to occur as a result of hydrogen (H) isotope permeation and trapping in W. In this study, two polycrystalline W plates were implanted with 80 keV H₂⁺ ions to a fluence of 2 × 10²¹ H⁺/m² at room temperature (RT). Time-of-flight secondary ion mass spectrometry (ToF-SIMS), focused ion beam (FIB), and scanning electron microscopy (SEM) were used for sample characterization. The SIMS data shows that H atoms are distributed well beyond the ion projected range. Isochronal annealing appears to suggest two H release stages that might be associated with the reported activation energies. H release at RT was observed between days 10 and 70 following ion implantation, and the level was maintained over the next 60 days. In addition, FIB/SEM results exhibit H₂ blister formation near the surface of the as-implanted W. The blister distribution remains unchanged after thermal annealing up to 600 ?C.     

Metallurgical characterizations of Fe–Cr–Ni–Zr base alloys developed for geological disposal of radioactive hulls

Alloy melting route is currently being considered for radioactive hulls immobilization. Towards this, wide range of alloys, belonging to Zirconium–Iron binary and Zirconium–Stainless steel pseudo-binary systems have been prepared through vacuum arc melting route. Detail microstructural characterization and quantitative phase analyses of these alloys along with interaction study between Zirconium and Stainless steel coupons at elevated temperatures identify Zr(Fe,Cr)₂, Zr(Fe,Cr), Zr₂(Fe,Cr), Zr₃(Fe,Ni), Zr₃(Fe,Cr), Zr₃(Fe,Cr,Ni), β-Zr and α-Zr as the most commonly occurring phases within the system for Zirconium rich bulk compositions. Nano-indentation studies found Zr(Fe,Cr)₂ and Zr(Fe,Cr) as extremely hard, Zr₃(Fe,Ni) as moderately ductile and β-Zr, Zr₂(Fe,Cr) as most ductile ones among the phases present. Steam oxidation studies of the alloys, based on weight gain/loss procedure and microstructural characterization of the mixed oxide layers, suggest that each of the alloys responded to the corrosive environment differently. Fe₂O₃, NiFe₂O₄, NiO, monoclinic ZrO₂ and tetragonal ZrO₂ are found to be most common constituents of the oxide layers developed on the alloys. Integrating the microstructural, mechanical and corrosion properties, ZrFeCrNi3 (Zr: 84.00, Fe: 11.20, Cr: 3.20, Ni: 1.60, in wt.%) is identified as the acceptable base alloy for disposal of radioactive hulls.     

Measurement of hydrogen permeation due to atomic flux using permeation probe in the spherical tokamak QUEST

Particle retention and recycling in plasma fusion devices are generally associated with the diffusion of atomic hydrogen into the materials. The resulted permeation of atomic hydrogen is known as plasma driven permeation (PDP). This permeation may also be significant, even in the walls, which are not directly exposed to the plasma. Under similar conditions, the permeation flux (Γ_perm) of hydrogen through a 30 μm thick Ni membrane heated at 412-575 K has been measured in the spherical tokamak QUEST. Γ_perm is being measured during the scans of different operating parameters like RF power (P_RF), chamber pressure (P_chamber), discharge widths (τ_dis) and vertical magnetic field (B_Z). Simultaneously edge plasma density and spectral intensities of atomic (Balmer) lines and molecular (Fulcher) bands have been compared with the permeation measurements. A linear relationship has been established between the time integrated Γ_perm i.e. permeation fluence (Q_perm) and the time integrated H_α intensity i.e. H_α fluence (Q_α). Q_perm also shows a strong relationship with the edge plasma density and various spectral fluences. The obtained results are discussed for exploring the applicability of the permeation probes in measuring the atomic flux near the first walls.