M. Hara, L. Wan, M. Matsuyama and K. Watanabe

Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    Absorption and desorption isotherms of protium and deuterium were measured for Pd-based alloys as Pd_(1-x)AE_x, where AE=Co, Ni, Cu, Rh, Ag, Pt and Au. It was observed that the heat of hydride formation decreased with increasing AE content for Co, Ni, Cu, Rh, Pt and Au, although the extent of the increase differed from each other. According to Lasser, on the other hand, alloying of Ag caused to increase the heat of hydride formation. These features were analyzed from electronic structures of the alloys inspected by use of DV-Xα package, where the inspections were carried out for small clusters as Pd_(14-y)AE_y. The DV-Xα calculations showed that the energy of the highest occupied molecular orbital of the clusters change almost linearly with their composition, suggesting that the Fermi energy of respective alloys changes in the similar manner. By assuming the Fermi energy of Pd_(1-x)AE_x to be arithmetic means of the Fermi energies of pure Pd and AE, a linear relation was found between the observed enthalpy change of hydride formation and the assumed Fermi energy.

Keywords: Pd-alloys, Hydride formation, Alloying effect, Fermi energy

J. Masuda^a, K. Hashizume^a, T. Otsuka^a, T. Tanabe^a, Y. Hatano^b, Y. Nakamura^c, T. Nagasaka^c, T. Muroga^c

^aInterdisciplinary Graduate School of Engineering Science, Kyushu University 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan

^bHydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

^cNational Institute for Fusion Science, 3226-Oroshi-cho, Toki, Gifu 509-5292, Japan

Abstract

    Tritium diffusion in a vanadium alloy (V-4Cr-4Ti) has been investigated at temperatures ranging from 230 K to 573 K. Tritium was loaded into the surface layers of the alloy specimen with an ac-glow discharge. Before and after diffusion annealing of the specimen, tritium diffusion profiles were measured by means of an imaging plate (IP) technique. Tritium diffusion coefficients (D_T), which were evaluated by fitting a numerical solution of the diffusion geometry employed here to the obtained diffusion profiles, were a little smaller than those for pure V with the activation energy of 0.13±0.01 eV. Below 320 K, in addition, the Arrhenius plot of D_T bent downwards showing a larger activation energy of 0.19±0.01 eV, probably owing to the trapping effect of both of Cr and Ti. The effect of alloying elements on tritium diffusion and the influence of tritium release from the surface were discussed.

Keywords: vanadium, tritium, diffusion

Y. Torikai, D. Murata, R.-D. Penzhorn, K. Akaishi, K. Watanabe and M. Matsuyama

Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555

Abstract

    BIXS measurements indicate that immersion into water or chemical etching of SS316 contaminated with tritium at moderate temperatures causes an immediate reduction of the outermost surface concentration of tritium. The fraction of surface tritium removed by water, i.e. 30 to 50 %, is small in comparison to the total tritium present in the specimen. Allowing a specimen to age whose surface and subsurface had been removed by etching up to a depth where the concentration of tritium is mostly constant revealed that within a few months a re-growth of tritium up to a saturation value higher than half of that originally present on the specimen takes place. Concurrently, a small but steady liberation of tritium at rates increasing from 0.1 to 0.3 kBq/h was noticed.

JNM Keywords: tritium and tritides, diffusion, steels, austenitic, low C/N, waste materials
PSI-17 Keywords: stainless steel, tritium retention, tritium removal

Y.Jin, L.Wang, M.Hara and K.Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

   Absorption kinetics of protium and deuterium for Pd, Pd-4 at%Pt and Pd-8 at%Pt were studied in a dilute hydorogen concentration region in a temperature region from 274 to 357 K by means of constant volume method, where samples were annealed well at 973K under vacuum before measurements to remove defects induced by sample preparation. It was found that protium had larger rate constants for absorption, lower rate constants for desorption and larger diffusion constants than those of deuterium within the examined temperature region. The activation energy of hydrogen absorption for both hydrogen isotope was almost null for all of the samples used. The activation energy of desorption for deuterium was smaller than that for protium. It was attributed to the difference in the enthalpy of hydrogen absorption into metal in dilute hydrogen concentration region between protium and deuterium. These features and trends observed in the alloying effect were supported by the ab initio calculations for small clusters. [doi:10.2320/matertrans.48.560]

Keywords: palladium alloy, kinetics, isotope effect, hydrogen absorption, hydrogen desorption, diffusion

鳥養祐二, 直江省吾, 赤石憲也, 渡辺国昭, 松山政夫

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

   To understand the release mechanism of tritium from solid materials,release rate of tritium was measured when a tritium loaded 316 stainless steel specimen was put in dry argon gas flow of atmospheric pressure at room temperature. During blowing of argon gas realeased products from the specimen were collected in water bubblers which were set in the downstream of the blowing circuit, and the tritium content in the bubbler water wae periodically measured as a function of time by scintillation counter. More than 99% of realesed species from the specimen was toritiated water, HTO. The measured result of tritium realease rate showed that tritium is released chronically for a long time. The chronic realese rate of tritium was evaluated using the diffusion model reported by Calder and Lewin, and it was found that when a reasonable value for the bulk diffusion coefficient of tritium is assumed, the tritium realese rate can be described with the diffusion flux at the surface boundary of the specimen.

Masao Matsuyama, Yuji Torikai, Masanori Hara and Kuniaki Watanabe

Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan

Abstract

   To establish a new technique for monitoring and control of high-level toritium in a fuel circulation system of the fusion reactors, applicability of a new tecnique to elemental tritium and tritiated water was discussed. The new technique is based on the utilization of x-rays induced by β-rays from tritium,and it is called β-ray-induced x-ray spectrometry. Applicability of the same technique to the tritium species retained in solid materials was also discussed. It was concluded from applications to gaseous and aqueous tritium under the static state that the new technique plays an important role in non-destructive evaluation of tritium retained in solid materials such as a plasma-facing materials.

A. Livshits^a, Y. Hatano^b, V. Alimov^a, M. Matsuyama^b

^aBonch-Bruyevich University, 61 Moika, 191065 St. Petersburg, Russia
^bHydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan

Abstract

    Energy dependence of the absorption/implantation probability, α_ab, of H₂⁺ ions in vanadium covered by an oxygen monolayer was studied in the range 0.5 to 300 eV by plasma-membrane techniques. In contrast to what one would expect in the case of a clean surface, α_ab was found: (1) to be appreciably smaller than 1 (α_ab ≈ 0.2) at the lowest energies, and, (2) to monotonically increase with ion energy, with a particularly steep rise in the range 0.5 to ∼7 eV − just where α_ab is expected to sharply decrease at a clean surface.

Keywoeds: Hydrogen, Hydrogen and Hydrides, Implantation, Ion Irradiation, Ion-surface interaction, Permeation, Surface Effects, Vanadium

M. Matsuyama, H. Sugiyama, M. Hara and K. Watanabe

Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan

Abstract

   To develop a new material for hydrogen isotope separation, absorption and desorption isotherms of protium(H¹₁)and deuterium(H²₁)were measured for five kinds of Pd-Cu alloys in the temperature range from283 to 453K. Thermodynamic parameters for the formation and decomposition of hydride and deuteride of the alloys,ΔH⁰and ΔS⁰, were evaluated from the temperature dependence of equilibrium pressure in a plateau region of the isotherms for each Pd-Cu alloy. The thermodynamic parameters for Pd-15at.%Cu alloy were almost equivalent to those of the Pd-8at.%Pt alloy which showed good separation performance. Separation tests of the 50%H₂-50%D₂ mixture were carried out under various conditions by using Pd-15at.%Cu alloy, and significantly high separation efficiency was observed. It was suggested,therefore, that the Pd-Cu alloys are applicable to the separation of hydorogen isotopes near room temperature.

(C)2007 Elsevier B.V.All rights reserved.

Yuji Hatano, Keita Ishiyama, Hirofumi Homma, Kuniaki Watanabe

Hydrogen Isotope Research Center, University of Toyama, Toyama, 930-8555, Japan

Abstract

    Niobium subcarbide (Nb₂C) was chosen as a material for non-porous intermediate layer to improve the high temperature durability of Pd-Nb composite membranes for hydrogen separation. A layer of Nb₂C was prepared between Nb substrate and thin Pd films (100nm), and the stability of Pd coating at elevated temperatures (573-773K) was examined by hydrogen absorption experiments. Hydrogen permeability through the Nb₂C layer appeared to be sufficiently high, and no noticeable deterioration was observed in hydrogen absorption rate under as-prepared conditions. The degradation in coating effect of Pd at elevated temperatures was substantially mitigated by Nb₂C layer. Such improved durability was ascribed to retardation of open porosity development by Nb₂C caused as a consequence of impeded interdiffusion between Pd and Nb.

Keywords: Hydrogen; Purification; Separation; Membrane; Palladium; Niobium; Durability

H. Homma ^a, Y. Hatano ^a, H. Daifuku ^b, H. Saitoh ^b, T. Nagasaka ^c, T. Muroga ^c, M. Hara ^a,, Y. Nakamura ^c, M. Matsuyama ^a,

^aHydrogen Isotope Research Center, University of Toyama, Toyama, 930-8555, Japan

^bDepartment of Materials Science and Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan

^cNational Institute for Fusion Science, Toki 509-5292, Japan

Abstract

    Tritium was loaded into cold-rolled and recrystallized specimens of a V-4Cr-4Ti alloy(NIFS-HEAT-2) at 673 K by a gas absorption method, and macroscopic distributions of tritium concentration in the specimens were examined by means of imaging plates. In the cold-rolled specimen, the distribution of tritium concentration was not uniform; bands of tritium-accumlated regions were observed along the rolling direction. Such bands of tritium-accumlated regions remained clearly visible even in the specimen recrytallized at 1173 K for 2 h. A more uniform concentration distribution, however, was observed for the specimen annealed at 1273 K for 2 h. The correlation between microstructure and tritium distibution is discussed.

Masateru Nose ¹*, Tokimasa Kawabata ², Miki Ohi ³, Takekazu Nagae ⁴, Seiichi Masa ³, Yuji Hatano ⁵, Susumu Ikeno ², Kiyoshi Nogi ⁶

¹Faculty of Art and Design, University of Toyama, 180 Futagami-machi, Takaoka 933-8588,Japan

²Faculty of Engineering,University of Toyama, 3190 Gofuku930-8555, Japan

³Hokunetsu Co.Ltd., 115 Takagi-nishi, Toyama 930-0106, Japan

⁴Toyama Industrial Reserch Center, 150 Futagami-machi, Takaoka 933-0981,Japan

⁵Hydrogen Isotope Research Center, University of Toyama, 3190 Gofuku 930-8555, Japan

⁶Joining and Welding Reserch Institute, Osaka University, 11-1 Mihogaoka, 567-0047 Japan

Abstract

   In die casting, soldering of the core pin surface is mainly resposible for dimensional tolerance failure of products. A newly designed protective of coating for die casting, consisting of TiAlN and amorphous carbon (a-C) with low soldering of magnesium, has been developed by the deposition of reactive cosputtering of TiAl and graphite targets using a UBM sputtering system. Structure analysis by GAXRD, HRTEM,laser Raman spectroscopy, and XPS revealed that the TiAlN/a-C coating has a nanocomposite structure consisting of a complicated mixture of nanocrystalline Ti-Al-N phase and a-C phase. Application of this coating to core pin for magnesium die casting demonstrated the lower tendency to adherence of magnesium alloy than TiAlN coating and longer lifetime with a total number of 〜276000 injections.

Keywords: adhesion; nanocomposities; PVD; surface modification; TEM

Masanori Hara¹, ^*1,Junichi Sakurai², ^*2, Satoshi Akamaru¹, Kiyomi Hashizume³, ^*3, Katsuhiko Nishimura², Katsunori Mori², Toshio Okabe³, Kuniaki Watanabe¹ and Masao Matsuyama¹

¹Hydrogen Isotope Research Center, University of Toyama 930-8555, Japan

²Faculty of Engineering, University of Toyama 930-8555, Japan

³Faculty of Science, University of Toyama 930-8555, Japan

Abstract

    Thermodynamic and magnetic properties of the Pd_0.93 Ag_0.07 hydrides were measured. The isotherms of Pd_0.93 Ag_0.07 -H and-D systems in the temperature range 373-523 K showed the plateau regions to be within 0.05<[Q(Q=H or D)]/[Pd_0.93 Ag_0.07 ]<0.4. From an investigation of the thermodynamic isotope effect for the formation and decomposition of hydride, the enthalpy changes, ΔH° _β→α'for desorption of hydrogen and deuterium were evaluated to be 43.0 kj/mol_H2 and 36.4kj/mol_D2, and renpectively. It was observed that the magnetization of Pd_0.93 Ag_0.07H_x at ambient temperature increased with increasing magnetic field. Since the magnetization was not saturated up to 7T, it can be concluded that _0.93 Ag_0.07H_x is paramagnetic. The magnetic susceptibility of Pd_0.93 Ag_0.07H_xprogressively decreased with increasing hydrogen content and vanished at [H]/[ Pd_0.93 Ag_0.07]=0.4. The disappearance of the susceptibility coincided with the termination of the plateau region of the isotherms. This fact can be explained by the rigid band model,according to which the vacant part of d-band of Pd_0.93 Ag _0.07can accept electrons from absorbed hydrogen atoms.

Takayuki Abe , Hiromi Hamatani,Shingo Higashide, Masanori Hara, Satoshi Akamaru

Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    Surface coating of small SiO₂ flakes with a WO₃ thin film was carried out by using a hexagonal-barrel-sputtering method. In order to find suitable sputtering conditions using this method, the WO₃ film was coated on the glass plate by reactive sputtering under desired total pressures, oxygen fractions, and substrate temperatures. By the analysis of XRD patterns, the suitable conditions prepared for the WO₃ film were determined to be a total pressure of 0.6 Pa, an oxygen fraction of 35% and 648 K. Surface coating of SiO₂ particles by WO₃ film was carried out under the conditions. It was found from SEM and EDS measurements that the surface of SiO₂ particles was coated with a thin uniform WO₃ film.

Keywords: Barrel-sputtering method; WO₃; Surface coating; Powdery materials

Akira Taguchi^a, Tomohito Kitami^b, Hironari Yamamoto^a, Satoshi Akamaru^a, Masanori Hara and^aTakayuki Abe^a

^aHydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

^bNippon Pillar Packing Co. Ltd., 541-1 Utsuba, Shimo Uchigami, Sanda, Hyogo 669-1333, Japan

Abstract

    Micron-sized spherical polymer particles were homogeneously coated with Au, Ag, Pd, Cu, and Ni by the barrel sputtering technique. Surface coating was successfully performed independent of the sputtered metal and the diameter of the polymer particles used. Optical microscope observations revealed a mirror-like appearance with a color that depended on the coated metal. SEM and EDX studies revealed that the surface of metal-coated samples was very smooth and the sputtered metal was homogeneously distributed over the entire sample surface. The amount of coated metal was evaluated using TG?DTA and ICP-AES measurements. The thickness of the metal film was within several 10 nm.

Keywords: Barrel sputtering system; Surface coating; Powdery materials

Akira Taguchi^a, Tomohito Kitami^b, Satoshi Akamaru^a and Takayuki Abe^a,

^aHydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

^bNippon Pillar Packing Co. Ltd., 541-1 Utsuba, Shimo Uchigami, Sanda, Hyogo 669-1333, Japan

Abstract

    Our newly developed “barrel-sputtering” technique has been employed for the surface coating of solid substrates with complex shapes such as bolts, nuts, and screws. The entire surface of the iron bolts and nuts including the flank and the root in the thread is homogeneously coated with the Au film. SEM measurements reveals that the surface of the Au film is very smooth. In the SEM measurements of the cross-sectional area, it is found that the Au film possess uniform thickness without any significant defects and/or pits. The Au film coating can also be successfully conducted on polycarbonate bolts and small SUS screws. The results provide evidences that the sputter deposition takes place in “three-dimensionally.”

Keywords:Barrel-sputtering system; Surface coating; Environment friendly process

Takayuki Abe, Shingo Higashide, Mitsuhiro Inoue and Satoshi Akamaru

Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract

   Abstract Fine particles were modified with a thin film of SnO2 by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO2 were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal SnO2 were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO2. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin film of SnO2 in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W.

These measured thicknesses coincided with the values estimated from the interference colors of the samples.

Keywords Sputtering - Coatings - Oxides - Optical reflectivity - Powder processing

Y. Mishima^a, N. Yoshida^b, H. Kawamura^c, K. Ishida^d, Y. Hatano^e, T. Shibayama^f, K. Munakata^b, Y. Sato^g, M. Uchida^h, K. Tsuchiya^c, S. Tanakaⁱ

^a Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, G3-23-4259, Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan
^b Kyushu University, 6-1 Kasugakoen, Kasuga-ku, Fukuoka, Fukuoka 816-8580, Japan
^c Japan Atomic Energy Agency, Narita, Oarai, Higashiibaraki, Ibaraki 311-1393, Japan
^d Tohoku University, Aobayama 02, Sendai, Miyagi 980-8579, Japan
^e The University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
^f Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-8626, Japan
^g Akita University, 1-1 Tegata Gakuen-machi, Akita 010-8502, Japan
^h NGK Insulators, Ltd., Maegata, Handa, Aichi 475-0825, Japan
ⁱ The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract

    Recently, several research and development (R&D) programs of beryllium and its alloys for fusion reactor application have been conducted in Japan and the community of beryllium research has grown. In the R&D area of beryllium technology for a solid breeding blanket, a major subject is applications of beryllides, for which lifetime evaluation as neutron multiplier, impurity effect on irradiation behavior and recycling of irradiated materials are under investigation. As for neutron multiplier materials, recent R&D has focused on Be.Ti alloys based on Be12Ti as an advanced option, because of their superior properties compared with beryllium metal in such respects as compatibility with structural materials and oxidation resistance at higher temperatures. In this paper, recent results on beryllide R&D in Japan are described.

K. Hashizume^a, J. Masuda^a, T. Otsuka^a, T. Tanabe^a, Y. Hatano^b, Y. Nakamura^c,
T. Nagasaka^c, T. Muroga^c

^a Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan
^b Hydrogen Isotope Research Center, The University of Toyama, Toyama 930-8555, Japan
^c National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

Abstract

    Tritium diffusion behavior in a V-4Cr-4Ti (NIFS-Heat-2) alloy has been examined with a tritium tracer technique. Firstly, a small amount of tritium (T) was implanted into the specimen surface, and then the specimen was diffusionannealed at temperatures ranging from 373 K to 573 K. The diffusion depth profile of T in the specimen was measured with a tritium imaging plate (IP) technique to determine the diffusion coefficient. The obtained diffusion coefficient of tritium in V-4Cr-4Ti is expressed as
D₁(cm²/s)=(7.5±0.2)*10^-4exp(-0.13(eV)/kT)
which is lower than that in pure vanadium, and is comparable with literature values of protium in a V-4Ti alloy taking the isotope mass effect into consideration.

Yuji Hatano, Keita Ishiyama, Hirofumi Homma, Kuniaki Watanabe

Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan

Abstract

    Non-porous intermediate layers comprising NbC and Nb₂C were prepared between thin Pd films (100 nm) and Nb substrates, and the high temperature stability (573-873 K) of Pd coating was examined by hydrogen absorption experiments. This type of intermediate layer provided better stability of Pd coating at/below 673K than the layers consisting solely of Nb₂C. Sharp reduction and recovery in hydrogen absorption rate were observed after heat treatments at 773 and 873 K, respectively. The mechanism underlying such complicated temperature dependence was discussed.

Yuji Hatanoa
^a,Kuniaki Watanabe^a,Alexander Livshits^b, Andrei Busnyuk^b, Vasily Alimov^b,Yukio Nakamura^c, Ken-ichi Hashizume^d

^aHydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan
^bBonch-Bruyevich University, 61 Moika, St. Petersburg 191186, Russia
^cNational Institute for Fusion Science, Toki 509-5292, Japan
^dDepartment of Advanced Energy Engineering Science, Kyushu University, Hakozaki 812-8581, Japan

Abstract

    Nonmetallic impurities segregated onto metal surfaces are able to drastically decrease the chemical reactivity of metals. In the present paper, effects of bulk impurities on the reactivity of metallic surfaces were investigated in a wide temperature range on an example of the sticking of hydrogen molecules and atoms to Nb [polycrystalline, with mainly (100)] containing solute oxygen. At all the investigated surface temperatures, T_S (300-1400 K), we found the bulk oxygen concentration C_O to have a strong effect on the integral probability,
α_H2 , of dissociative sticking of H₂ molecules followed by hydrogen solution in the metal lattice: α_H2 monotonically decreased by orders of magnitude with increasing C_O from 0.03 to 1.5 at. %. The sticking coefficient α_H2 was found to depend on T_S but not on the gas temperature. The effect of C_O on α_H2 is explained by the presence of oxygen-free sites (holes in coverage) serving as active centers of the surface reaction in the oxygen monolayer upon Nb. In contrast to H₂ molecules, H atoms were found to stick to, and be dissolved in, oxygen-covered Nb with a probability comparable to 1, depending neither on C_O nor on T_S. This proves that, unlike H₂ molecules, H atoms do stick to be dissolved mainly through regular surface sites covered by oxygen and not through the holes in coverage.

Yuji Hatano¹, Andrei Busnyuk², Alexander Livshits², Yukio Nakamura³, Masao Matsuyama¹

¹University of Toyama, Gofuku 3190, Toyam 930-8555, Japan
²Bonch-Bruyevich University, 61 Moika, St. Petersberg 191186, Russia
³National Institute for Fusion Science, Toki 509-5292, Japan

Abstract

    In order to understand the capability of vanadium panels and membranes for fuel particle pumping at relatively low temperatures, absorption of neutralhydrogen atoms by vanadium sheet was examined at/below 350°C under wide variety of experimental conditions. A niobium sheet kept at high temperature (420°C) was used as a reference specimen. Sufficiently high absorption rates were obtained even at around room temperature in the range of incident fluxes from 10¹⁷ to 10²¹ m^-2s^-1. No noticeable reduction in absorption rates was observed up to the H retention level of 0.1 at%. The influence of CO and water vapor was negligibly small up to an exposure of 10²³ m^-2. Significant reduction in the absorption rate was observed only when an oxide film was formed on the surface by exposure to O₂ to 10²⁰ m^-2 and to H₂O over
10²³ m^-2 at room temperature.

Yuji Hatano¹, Andrei Busnyuk², Alexander Livshits², Hirofumi Homma¹, Masao Matsuyama¹

¹University of Toyama, Gofuku 3190, Toyam 930-8555, Japan
²Bonch-Bruyevich University, 61 Moika, St. Petersberg 191186, Russia

Abstract

    Niobium is a potential candidate of tube material in vacuum permeator for tritium recovery from Pb-17Li liquid blanket system. From this viewpoint, the permeation of hydrogen through a Nb membrane was investigated with an ultra-high vacuum apparatus under the conditions relevant to the blanket system where no oxide films could be retained on the membrane surfaces. It was, however, found that the permeation rate sharply decreased with increasing oxygen concentration in the bulk of membrane; at upstream H2 pressure of 1 Pa and membrane temperature of 700°C, for example, the permeation rate at oxygen concentration corresponding to oxygen potential in Pb-17Li (0.054 at%) was evaluated to be 1/5 of the value expected from hydrogen solubility and diffusivity in Nb. Such small permeation rate was ascribed to the presence of oxygen monolayer formed by surface segregation from the bulk. Surface modification by Pd coating was found to give only limited improvement due to degradation in coating effect induced by interdiffusion between Pd and Nb. Methods to improve the high temperature stability of Pd coating was discussed.

T.Sakamura, H.Saitoh, H.Homma, Y.Hatano, T.Nagasaka, T.Muroga, Y.Nakamura

¹Muroran Inst Technol, Dept Mat Sci & Engn, Muroran, Hokkaido 0508585 Japan
² Toyama Univ, Hydrogen Isotope Res Ctr, Toyama 9308555, Japan
³ Natl Inst Fus Sci, Toki 5095292, Japan

Abstract

    Tritium radioluminography has been applied to the observation of tritium distribution in electro-chemically tritium charged pure V and V-4Cr-4Ti alloy (NIFS-HEAT-2) specimens, and the relation between the tritium distribution and the microstructure has been examined.
 In the cold rolled V-4Cr-4Ti alloy specimen, tritium distribution showed band-like morphology along the rolling direction. This tritium accumulated band is corresponded to the band-like structure formed by high densely precipitated fine Ti granules. On the other hand, band-like morphology of tritium accumulation was not observed in the pure V and Ti-precipitation free V-4Cr-4Ti alloy specimen. The Ti-precipitate is concluded to be a strong trapping site for tritium. The tritium segregation to the grain boundary was not recognized both in the pure V and V-4Cr-4Ti alloy specimen indicating that the trapping power of the grain boundary for tritium is weak.