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[1991_01]
Journal of Nuclear Materials, 183 (1991) 274-276
Letter to the Editors
Kuniaki Watanabe, Kan Ashida and Masao Matsuyama
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
[1991_02]
Journal of Nuclear Materials, 183 (1991) 89-95
Kan Ashida and Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
The diffusion constants of tritium and/or its isotope for graphite so far reported scatter considerably in the Arrhenius plot diagram. This, however, has not been seriously considered, despite that the understanding of the scattering is indispensable to estimate the tritium inventory and permeation in/through the graphite first walls of D-T burning experimental devices. We show in the present paper that there is regularity in the scattering: namely, the presence of a linear relation between the logarithms of the pre-exponential factors and the activation energies (the compensation effect). The temperature dependence of the diffusion constants and the compensation effect were analyzed by assuming the presence of three distinct diffusion channels in graphite: channels along the a- and c-axis in a graphite grain and along the grain boundary. Computational simulations could reproduce fairly well the temperature dependence of the experimental data and the compensation effect by assuming proper effective pre-exponential factors for the respective channels, where the activation energies for the respective channels were chosen from the observed values. Namely, the scattering of the diffusion constants and the compensation effect can be interpreted as a consequence of the multi-diffusion channels.
[1991_03]
Journal of Nuclear Materials, 183 (1991) 195-201
Kuniaki Watanabe, Kan Ashida, Masao Matsuyama, Hitoshi Miyake
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
Attention has been to several Li-compounds which are expected to be tritium breeding materials in thermonuclear fusion reactors. Diffusion constants of tritium for them reported so far by many investigators, however, differ considerably from each other, even for a given material. We looked at the diffusion constants of tritium for Li2O, LiX (X=F, Cl, Br, I), Li-Pb, and LiF-MF2 (M=Be, Pb) and found regularity on the scatters of the diffusion constants. Namely, there was a linear relation as In(D0) =αEd +β, where D0 and Ed are the pre-exponential factors and activation energies for the diffusion constants of hydrogen in relevant materials. It is a similar phenomenon known as the "compensation effect" in chemical reactions. In the light of this concept, the scatters of the diffusion constants for a given system could be interpreted as a consequence of the difference in diffusion channels and/or in free energy change for tritium capture in relevant materials.
[1991_04] *The text is Japanese.
J. Vac. Soc. Japan, 34 (1991) 158-161
Hitoshi Miyake, Kan Ashida, Masao Matsuyama, Kuniaki Watanabe, Mitsuru Sakurai
Abstract
To examine tritium contamination/decontamination
characteristics of turbomolecular pumps, which are regarded as potential
candidates of vacuum and/or circulation pumps in large scale tritium handling
systems, we measured the ad/absorption of tritium on/in the component materials
of a turbomolecular pump (TG600M, Osaka Vacuum).
It was observed that the amount of adsorption
was in the order of [MoS2 coated metals] > [organic materials] > [metals], and that of absorption
was [organic materials] > [MoS2 coated metals] > [metals]. The overall tritium inventory in this pump
was found to be at a rather low level, about 2.5 GBq, after being exposed
to the tritium gas amounting to about 2 × 105 Pa·sec.
The tritium ad/absorbed on/in the materials could be removed easily with
vacuum heating above 200 °C, but below this temperature it was hard
to remove most of ad/absorbed tritium. From the view point of safety and
environmental aspects, however, it is required to develop suitable decontamination
techniques and contamination free materials.
[1991_05]
Fusion Engineering and Design, 18 (1991) 27-32
Kuniaki Watanabe, Kouri Tanaka, Masao Matsuyama and Kiyoshi Hasegawa*
Hydrogen Isotope Research Center, *Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
Reversible tritium getters are indispensable for
the safe handling of a large amount of tritium in the fuel processing for
thermonuclear fusion reactors. In Zr-Ni metallic compounds, we looked for
the reversible getters showing the heat of deuteride formation around -25
kcal/mol (D2) which will be appropriate to the storage-supply-recovery
of tritium.
Among five metallic compounds used in this study,
we found that the first plateau for ZrNi and Zr9Ni11
showed ΔH0 = -25 kcal/mol (D2).
The second plateau for ZrNi gave ΔH0
= -19.2 kcal/mol (D2). This suggests that ZrNi is also applied
as the source of tritium supply near one atmosphere at relatively low temperature
(260 °C). They were withstanding pulverization and nonflammable against
air exposure. In addition, ZrNiD2.3 was reactivated quite easily
with vacuum heat at 300 °C even after air exposure. Those properties
of ZrNi and/or Zr9Ni11, are quite promising as the
reversible tritium getter in the fuel processing for thermonuclear fusion
reactors.
[1991_06]
Fusion Engineering and Design, 18 (1991) 91-96
Masao Matsuyama and Kuniaki Watanabe
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
Small sized ionization chambers are attractive as a continuous tritium flow monitor in the fuel processing systems. We made a small ionization chamber and examined some basic properties of it such as saturation-current characteristics, concentration and/or pressure dependence of the ionization current, and impurity gas effects. A small ionization chamber of 1.9 cm3 in volume showed satisfactory saturation-current characteristics above 20 V, and also gave a good linear relationship between ionization current and tritium concentration in a wide range from 1 × 10-6 to 3 × 10-1 Ci/cm3 under condition of 1 atm. The pressure dependence of the ionization current was analyzed through a simple two-dimensional model taking account of the energy consumption of ß particles in the chamber. Addition of inert gas caused the ionization current to increase. This phenomenon was attributed to the change in the stopping power and W value with the mixing up of different gases.
[1991_07]
Appl. Radiat. Isot., 42(12) (1991) 1153-1158
MASAO MATSUYAMA, KAN ASHIDA and TOYOSABURO TAKEUCHI
Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
The reduction behavior of powdered Fe-Ni oxides
in a hydrogen atmosphere at 380 °C was studied by means of radioactive
tracer of
63Ni. Change in the radioactivity of the surface gives
information on mutual diffusion of Fe and Ni between surface and bulk during
the reduction process.
The radioactivity of 63Ni in the surface
layer of the alloy oxides increased with the progress of reduction in the
initial stages and then drastically decreased, suggesting that Ni is covered
with metallic Fe at the final stage of reduction. X-Ray diffraction showed
that unreduced Fe-Ni oxides were composed of a mixture of Fe2O3
(hematite) and NiO, and the reduced alloys were composed of homogeneous
Fe-Ni and Fe or Ni. Fe2O3 was changed to Fe3O4
(magnetite) before metallic Ni appeared, and metallic Ni appeared earlier
than Fe-Ni. Metallic Fe appeared after Fe-Ni, and no FeO was detected throughout
the reduction.
The following reactions were proposed to be involved
in the reduction mechanism; FeO + Fe2O3--> Fe3O4
and NiO + Fe + Fe2O3--> Ni + Fe3O4.
It was also concluded that an Fe-rich surface is formed by the belated
diffusion of Fe to metallic Ni, which is produced earlier than metallic Fe.