K. Ashida^a, K. Kanamori^b, K. Ichimura^a, M. Matsuyama^a, K. Watanabe^a

^a Tritium Research Center, Toyama University
^b Department of Chemistry, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930, Japan

K. Ashida, K. Ichimura, K. Watanabe

Abstract

    Hydrogen isotopes implanted into graphite show broad thermal desorption spectra, which comprise three desorption peak denoted as peak Ⅰ. Ⅱ and Ⅲ with increasing peak temperature. This study was devoted to deconvoluted the spectra with the aid of a stepwise detrapping method and to understand their desorption mechanisms. It was found that the peak Ⅰ and Ⅱ obeyed the second order kinetics with respect to the amount of trapped isotope atoms. This indicates that the rate determining steps for desorption are the recombination reactions of the trapped isotope atoms. The kinetic parameters determined are as follows: for peak Ⅰ as

K_Ⅰd(H₂) = (1.5 × 10^-6) exp (-43 × 10³/RT)

K_Ⅰd(D₂) = (4.0 × 10^-7) exp (-44 × 10³/RT)

K_Ⅰd(T₂) = (9.3 × 10^-6) exp (-45 × 10³/RT)

  And for peak Ⅱ as

K_Ⅱd(H₂) = (7.5 × 10^-4) exp (-59 × 10³/RT)

K_Ⅱd(D₂) = (2.4 × 10^-4) exp (-59 × 10³/RT)

K_Ⅱd(T₂) = (1.3 × 10^-3) exp (-59 × 10³/RT)

    Where the frequency factor and activation energy are in [/molec. S] and [cal/mol] units, respectively. The considerably deviated frequency factors for T₂ appeare due to the presence of impurity gases, such as H₂O, CO, CO₂, and so on, in the tritium gas used.

Kenji Ichimura, Masao Matsuyama, Kuniaki Watanabe

Abstract

    Zr-alloy getters have been applied to tritium handling and vacuum conditioning for fusion devices because of remarkably low dissociation pressure of hydride and large pumping speed for hydrogen, oxygen and carbon monoxide. For the application to tritium processing in fusion reactors, however, some of their properties should be improved. As a first step, we have examined the activation process of Zr₂Ni alloy using surface analysis equipments. In addition, absorption and desorption processes of hydrogen isotopes and isotopic waters were examined by thermal desorption spectroscopy. It was observed that the metallic Zr appeared by vacuum has above 400℃. As a consequence, the alloy showed pumping action for various gases. It was revealed that the rate determining step in the absorption process is the dissociation of adsorbed molecules, while the rate determining step in the desorption process is the surface association of adsorbed atoms. The isotopic effects on activation energy for the absorption of hydrogen isotopes and isotopic waters were observed: 0.63 for H₂, 0.86 for D₂, and 0.72 for H₂O and 1.6 kcal/mol for D₂O. Similar isotopic effect was also observed for the desorption of hydrogen isotope molecules. The isotopic effects differed from each other for different alloys.

K. Watanabe, K. Ichimura

Abstract

    To develop getters suitable for tritium processing such as storage, supply, separation, and so on, we examined the alloying effects on the activation processes of Zr and Zr-alloys (Zr-Al, Zr-V-Fe, and Zr-Ni) by means of XPS-SIMS-TDS. It was observed that the formation of metallic Zr surface was the principal process for the activation, by which the getters showed pumping action for various gases. In the activation of Zr-alloys, a considerable alloying effect was observed: the activation temperature varied with alloying element. They were 900℃ for Zr, 800℃ for Zr-Al, 700℃ for Zr-Ni, and 400℃ for Zr-V-Fe. On the basis of surface characterization with XPS-SIMS and of TDS for impurity gases adsorbed on the as-received getter surface, it was concluded that the alloying effects on the activation temperature are determined with the balance between the stability of corresponding oxides and carbides present on the surfaces and the diffusivity of oxygen and carbon from the surface into the bulk.

K. Ichimura, K. Watanabe, M. Matsuyama, T. Takeuchi

Abstract

    Tritium processing such as supply, recovery, storage, and separation are of special importance for blanket technology as well as fuel cycling in fusion reactors. To obtain guiding principles to design suitable getters for each of the unit processes, we have studied the effects of alloying on the getter propertics using Zr-alloys. The activation energy for absorption varied considerably with alloying: it was 0.74 for Zr-Al, 0.01 for Zr-V-Fe, and 0.63 kcal/mol for Zr-Ni, whereas that for Zr has been reported as 19.2 kcal/mol. The heat of absorption also changed with alloying element as 32.0 - 33.4 (Zr-Al). That of hydrogen in Zr is reported as 15.6 - 30.6 kcal/mol. In addition, the ratio of the pumping sped of water vapor to that of hydrogen varied with alloying elements: for example, 1/40 for Zr-V-Fe and 1/4 for Zr-Ni at room temperature. The alloying effects mentioned above are considered due to modification of electronic structure of Zr with the alloying.

Kuniaki Watanabe, Kenji Ichimura, Naoya Inoue

Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    The hydrogen evolution rate in photoassisted decomposition of water by Pt/TiO₂ was significantly enhanced in the presence of tritium (90 - 180 mCi/ml). The extent of the enhancement was proportional to the tritium concentration. This effect is attributed to the synergism of β-rays from tritium and photons on this decomposition reaction.

Kuniaki Watanabe, Kenji Ichimura, Naoya Inoue, Ikuya Matsuura

Tritium Research Center and Faculty of Science, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    We measured first the hydrogen separation factor for the H₂O-HTO system in the photoassisted catalytic decomposition along with that for the H₂O-D₂O system. It was 15.4±0.2 for H₂O-HTO at the initial stage of the reaction. For H₂O-D₂O, it was 5.1±0.05 over a wide mixing ratio. These values are equivalent with those from electrolysis, indicating that the photoassisted decomposition proceeds with the same mechanism as the electrolysis. These results also confirmed that the catalytic process is the rate-determining step. The separation factors, however, decreased with reaction time to 6.2±0.05 (H₂O-HTO), 3.6±0.05 (H₂O-HDO), and 3.05±0.05 (D₂O-HDO) due to the gas-liquid equilibration reaction.

T. Miki^a, M. Ikeya^a, M. Matsuyama^b, K. Watanabe^b

^a Technical College, Yamaguchi University, Tokiwadai 2557, Ube 755, Japan

^b Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    The decrease of the electret charge by exposure to gaseous tritium was studied in order to develop an electret personnel dosemeter for tritium. The electret charge decreases in proportion to the product of the tritium activity and the exposure time, corresponding to the theoretical response of electret dosemeters in the ionization chamber mode. The sensitivity is high enough to be of practical use. Several outstanding problems, especially the compensation of the contribution from atmospheric radon to the electret charge reduction, are discussed. A hybrid type electret dosemeter is proposed to compensate for the contribution of atmospheric radon and background gamma rays.

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Masao Matsuyama^a, Kan Ashida^a, Osamu Takayasu^b, Toyosaburo Takeuchi^a

^aTritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

^b Faculty of Science, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    The surface compositions of three kinds of powdered alloys with different structures, Cu-Ni (fcc-fcc), Fe-Ni (bcc-fcc), and Co-Ni (hcp-fcc), were determined by the penetration of β-rays of ⁶³Ni mixed previously in the alloy, then the effect of the respective alloy structure both of the surface and of the bulk on the catalytic hydrogenation of ethylene was studied. The surfaces of these alloys were found to be Ni-poor for the wide range of alloy composition. The catalytic activity expressed by each surface composition was difficult to explain by the physicochemical properties of the surface. The activity expressed by the bulk composition of Cu-Ni of fcc structure was high in the region of unfilled d-band, and so were that of Fe-Ni and that of Co-Ni in the region of fcc structure. The activity of Fe-Ni for the dimerization of ¹⁴C-ethylene was studied, of whose activity the similar tendency was observed as found in the hydrogenation reaction. These could be interpreted as the results of the positive contribution of the dissolved hydrogen in bulk to the catalytic reactions.

松山政夫, 芦田 完, 竹内豊三郎

富山大学トリチウム科学センター　930　富山市五福3190

Abstract

    Fe-Niの酸化物から水素還元により粉体合金が生成する機作を知る目的で、還元途上 における表層のNiの濃度変化を、予め混入してある⁶³Niのβ線の自己吸収から知り、更にX線回折に よる構造変化をも調べた。表層の⁶³Niの量は還元終了近くで急激に減少した。またX線回折の結果、 Fe-Ni合金とFe又はNiが常に共存していること、合金の組成は平均組成よりも常にNi-richであること及び酸化鉄は その割合が小さくても還元の終了近くまで残ることなどが知られた。これらから、Fe-Ni酸化物中の酸化Niが先に 還元され、そのNiクラスターへ還元されたFe原子が拡散するために表面がFe-richになると結論した。
    [討論したい事項]　①表面がFe-richになる理由、②NiO中のFe₃O₄ の還元機作、③⁶³Ni法の適用性

Kuniaki Watanabe

Tritium Research Center, Toyama Univ.