研究報告　-　20巻　(2000年)

解説-Review

20-1

トリチウムの環境動態
Environmental Tritium

百島則幸

N. Momoshima

論文-Original

20-2

Zr₂Niの水素誘起不均化の動力学　-温度依存性-
Hydrogen Induced Disproportionation of Zr₂Ni  -Temperature Dependence-

原 正憲、金子義信、渡辺国昭

M. Hara, Y. Kaneko, K. Watanabe

20-3

Pｄ-Pt合金による水素吸収曲線の解析
Analysis of Hydrogen Absorption Kinetics for Pd-Pt Alloys

金　瑩、原　正憲、渡辺国昭

Y. Jin, M. Hara, K. Watanabe

20-4

タングステンとアモルファス炭素膜との固相反応
Solid State Reaction between Tungsten and Amorphous Carbon Film

波多野雄治、渡辺国昭、高森美幸、松田健二、池野進

Y. Hatano, K. Watanabe, M. Takamori, K. Matsuda, S. Ikeno

20-5

含水素炭素膜と金属基盤（Be, Mo, W）との反応動力学の解析
Kinetic Analysis of Reactions between Hydrogen-containing Carbon Film and Substrate Metals (Be, Mo, W)

芦田　完、波多野雄治、渡辺国昭

K. Ashida, Y. Hatano, K. Watanabe

20-6

b線誘起X線計測法による硼素コーティング黒鉛材料のトリチウム保持に関する検討
Examination of Tritium Retention in Boron-Coated Graphite by  b-Ray-Induced X-ray Spectrometry

松山政夫、村井忠幸、渡辺国昭、都築和泰、野田信明

M. Matsuyama, T. Murai, K. Watanabe, K. Tsuzuki, N. Noda

データ-Data

20-7

トリチウム増殖材データベース（5）　（TiO₂添加Li₂TiO₃固体増殖材）
Tritium Breeding Materials Data Base for Fusion Reactor Blankets (5) (TiO₂-doped Li₂TiO₃ Solid Breeding Materials)

二村嘉明、河村　弘、土谷邦彦

Y. Futamura, H. Kawamura, K. Tsuchiya

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研究報告20-1
解説

　Environmental tritium was first observed in a helium fraction at a liquid air production facility in Germany in 1949. During the 1950s and early 1960s, huge amounts of artificial tritium were released into the atmosphere by nuclear testing. The environmental tritium level increased to more than 200 times the natural tritium level. Since the signing of a test ban treaty in 1963, the environmental tritium level has decreased, and analysis of recent Japanese rain samples has shown that the environmental tritium level is close to that before the nuclear testing. Tritium released from nuclear bombs into the atmosphere has been used as a global-scale tracer in studies on water mass movement in the ocean, groundwater flow and atmospheric air mass movement. Useful and valuable results have been obtained in those studies. In the atmosphere, tritium exists in three different chemical forms: hydrogen (HT), water vapor (HTO) and hydrocarbons (CH₃T). The concentration of HT the highest, followed by those of CH₃T and HTO. The most interesting feature of these chemical species is their significantly different specific activities. HT has 10⁶ TU, CH₃T has 10⁴ TU and HTO has 10 TU, suggesting that HT and CH₃T have been released from nuclear facilities. Vegetation is sensitively responds to a change in environmental HTO level by rapid exchange of water molecules between leaf water and atmospheric water vapor. HTO vapor released into the air slowly contaminates soil water. A nuclear fusion facility is planed to use a large quantity of tritium that is comparable to natural tritium on the earth, indicating the necessity to maintain tritium in a nuclear fusion facility and the necessity to carefully monitor the environmental tritium level.

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研究報告20-2
論文

　The kinetics of hydrogen induced-disproportionation of Zr₂Ni was measured in a hydrogen atmosphere in a temperature range from 723 to 898 K. The disproportionation process of Zr₂Ni was found as Zr₂Ni + H₂ -> ZrH₂ + ZrNi. This reaction was completed within 100 s at all temperatures. The Avrami-Erofeev equation was used to analyze the reaction mechanism. It was found that the mechanism could be described by a nucleation and nuclei growth model. The activation energy for the disproportionation was determined to be -3 kJ/mol, which is slightly larger than that of Zr₂Co (-15 kJ/mol). The negative temperature dependence was examined by the decrease in the number of product nuclei, owing to the reduction of hydrogen solubility in the reactant phase, with increase in temperature.

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研究報告20-3
論文

　Hydrogen absorption kinetics of palladium alloys was studied by using a vacuum microbalance system. The data analysis procedures were shown in detail in the present paper for a spherical sample as an example, where the second order hydrogen adsorption and desorption were assumed to have occurred on the sample surface. The factors that may influence hydrogen absorption curves and kinetic parameters are discussed.

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研究報告20-4
論文

　Solid state reaction between tungsten and carbon film was examined at 1073K. Carbon film was deposited onto tungsten sheet by vacuum evaporation at room temperature and analyzed by means of X-ray photoelectron spectroscopy. Carbon and tungsten beneath the carbon film were detected, whereas only trace amount of impurities such as oxygen were present. The binding energy of W 4f electrons indicated that tungsten was in a metallic state at the interface. These observations suggested that no impurity layer existed at the interface. Analysis using transmission electron microscopy showed that carbon was in an amorphous state. The specimen was heated at 1073 K in vacuum, and change in crystal structure was analyzed by means of X-ray diffraction. The peak of W₂C appeared after an induction period for ca. 1 min, although W₂C is not thermodynamically stable at 1073 K. The peak intensity ratio of W₂C to metallic tungsten increased in proportion to the square root of time to take the maximum value at 50 min and then decreased with elapse of time. No peak of WC was observed. These results indicate that the nucleation rate of W₂C was much faster than that of WC at 1073 K. The decomposition of W₂C was ascribed to the reaction between carbon in W₂C and H₂O in residual gas.

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研究報告20-5
論文

　Kinetic analyses were performed for solid-state reactions between a hydrogen-containing carbon film and substrate metals to form metallic carbide of Me₂C (Me=Be, Mo, W). Isothermal and non-isothermal reaction curves could be explained by a random nucleation and two-dimentional crystal growth model. The kinetic equation can be approximated well by -ln(1-x)= k_appt^2, where x is the extent of reaction and kapp the apparent rate constant. The temperature dependence of the rate constants are given as

k_app(Be)=3.10 exp(-109.[kJ/mol]/RT) [1/sec²],

k_app(Mo)=231. exp(-161.[kJ/mol]/RT),

k_app(W) =516. exp(-183.[kJ/mol]/RT),

for Be-C, Mo-C and W-C systems, respectively, where the apparent activation energy is considered to be the sum of those for nucleation and diffusion. Linear relations were found between the apparent activation energy and the melting point of substrate metals as well as the bond strength of Me-C (Me=Be, Mo, W).

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研究報告20-6
論文

　Tritium retention in boron-coated graphite (B/Graphite) irradiated with tritium ions at room temperature and at high temperatures was examined by beta-ray-induced X-ray spectrometry (BIXS). The results of analyses by X-ray diffraction and X-ray photoelectron spectroscopy for an unirradiated sample suggested that boron coated on the graphite surface formed an amorphous structure and that it contained impurities such as oxygen and carbon. Both a sharp intense peak and a broad weak peak induced by beta-rays appeared in the observed X-ray spectra. It was seen from the X-ray spectra that most of tritium implanted into the B/Graphite at room temperature was retained on the surface and in subsurface layers. In addition, it was seen that the implanted tritium can be easily removed at a relatively low temperature and that the retention amount decreased to 1/3 by heating at 300゜C for 30 min. However, a considerable increase in tritium retention was observed when the irradiation temperature was increased to more than 300C, indicating adsorption of tritium on the bare surface graphite.

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研究報告20-7
データ

　Recently, lithium titanate (Li₂TiO₃) has attracted the attention of many researchers. Small pebble-like shapes of Li₂TiO₃ have been selected as the most suitable for the design of a fusion blanket. As the fabrication method of Li₂TiO₃ pebbles, the wet process is most advantageous from the view point of various factors such as mass production. However, the grain size oh Li₂TiO₃ pebbles fabricated by the wet process was larger than that of Li₂TiO₃ pebbles fabricated by the rotating granulation method. Therefore, materials such as TiO₂-doped Li₂TiO₃ that have improved properties such as microcrystal and moisture absorption properties have been developed.
  In this report, the thermal properties of TiO₂-doped Li₂TiO₃ pellets are evaluated.