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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)AEx, 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)AEy. 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)AEx 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. Masudaa, K. Hashizumea, T. Otsukaa, T. Tanabea, Y. Hatanob, Y. Nakamurac, T. Nagasakac, T. Murogac
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 (DT), 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 DT 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. Livshitsa, Y. Hatanob, V. Alimova, M. Matsuyamab
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, αab, 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, αab was found: (1) to be appreciably smaller than 1 (αab ≈ 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 αab 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 Pd0.93 Ag0.07 hydrides were measured. The isotherms of Pd0.93 Ag0.07 -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)]/[Pd0.93 Ag0.07 ]<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/molH2 and 36.4kj/molD2, and renpectively. It was observed that the magnetization of Pd0.93 Ag0.07Hx at ambient temperature increased with increasing magnetic field. Since the magnetization was not saturated up to 7T, it can be concluded that 0.93 Ag0.07Hx is paramagnetic. The magnetic susceptibility of Pd0.93 Ag0.07Hxprogressively decreased with increasing hydrogen content and vanished at [H]/[ Pd0.93 Ag0.07]=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 Pd0.93 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 Taguchia, Tomohito Kitamib, Hironari Yamamotoa, Satoshi Akamarua, Masanori Hara andaTakayuki Abea
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 Taguchia, Tomohito Kitamib, Satoshi Akamarua and Takayuki Abea,
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. Mishimaa, N. Yoshidab, H. Kawamurac, K. Ishidad, Y. Hatanoe, T. Shibayamaf, K. Munakatab, Y. Satog, M. Uchidah, K. Tsuchiyac, 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. Hashizumea, J. Masudaa, T. Otsukaa, T. Tanabea, Y. Hatanob,
Y. Nakamurac,
T. Nagasakac, T. Murogac
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 Hatanoaa,Kuniaki Watanabea,Alexander Livshitsb, Andrei Busnyukb, Vasily Alimovb,Yukio Nakamurac, Ken-ichi Hashizumed
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, TS (300-1400 K), we found the bulk oxygen concentration CO to
have a strong effect on the integral probability,
αH2
, of dissociative sticking of H2 molecules
followed by hydrogen solution in the metal lattice: αH2
monotonically decreased by orders of
magnitude with increasing CO from 0.03 to 1.5 at. %. The sticking coefficient αH2
was found to
depend on TS but not on the gas temperature. The effect of CO on αH2
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 CO nor
on TS. 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.