K. Ashida^a, K. Kanamori^b, K. Watanabe^a

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

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

Abstract

    Graphite is the primary candidate for the first wall of magnetically confined fusion devices. For this purpose, it is important to know the surface properties of graphite to understand the plasma-surface interaction as well as vacuum properties of graphite. From this viewpoint, we examined the binding states of carbon atoms, inherent hydrogen content, and crystallinity of the surfaces of isotropic graphites prepared by several Japanese companies as well as anisotropic ones with x-ray photoelectron (XPS), secondary ion mass (SIMS), and Raman (RS) spectroscopies. Although no measurable difference in the binding state of carbon atoms was detected among the isotropic and anisotropic graphites with XPS, RS revealed that their crystallite sizes differed from each other. Namely, the crystallite sized of the isotropic were in the range from 100 to 300 Å, whereas those of the anisotropic graphites were more than 〜 1000Å. In addition, nongraphitized carbon which was not observed for the anisotropic graphites was present in the surface layers of the isotropic ones. SIMS revealed that the inherenthydrogen contents in the isotropic graphites were larger than those in the anisotropic ones. The results indicate that the larger hydrogen contents in the isotropic graphites are due to the presence of nongraphitized carbon which acts as the trapping site of hydrogen atoms.

Kan Ashida, Masao Matsuyama, Kuniaki Watanabe

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

Abstract

    Graphite is the primary candidate for the first wall of magnetically confined fusion devices. For this application, it is important to know the surface properties and trap/release behavior of hydrogen isotopes to understand fuel recycling/inventory in the graphite first wall. The surface analysis of as-received graphite revealed that the inherent hydrogen content is larger in isotropic compared to the anisotropic graphite. This is due to the presence of non-graphitized carbon atoms in the isotropic graphite which act as the trapping sites of hydrogen atoms. Ion bombardment causes the reduction of the crystallite size of graphite (damage modification), leading to amorphous-like structure. The thermal desorption spectra of hydrogen isotopes consisted of three desorption peaks for the modified graphite. The desorption mechanisms and parameters of three peaks are determined. These parameters were used to estimate the fuel inventory in the graphite.

Kenji Ichimura, Masao Matsuyama, Kuniaki Watanabe, Toyosaburo Takeuchi

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

Abstract

    Zr-alloy getters have been applied to tritium handling and vacuum conditioning for fusion devices. Some of their properties, however, should be improved to apply them in future devices. From this viewpoint, we have studied the effects of alloying on the getter properties of Zr alloys. We found that the activation energy of absorption and desorption of hydrogen varied considerably with alloying. The activation energy for hydrogen absorption was 0.74 for Zr₆₁Al₃₉, 0.01 for Zr₅₇V₃₆Fe₇, 0.63 for Zr₆₇Ni₃₃, and 2.8 kcal/mol for Zr₈₅Ni₁₅ , whereas that for Zr was 2.6 kcal/mol. The heat of hydrogen absorption was 27.8 kcal/mol for Zr : it changed with alloying as 32.0-33.4 (Zr₆₁Al₃₉ ), 27.8-28.4 (Zr₅₇V₃₆Fe₇), 29.0 (Zr₆₇Ni₃₃), and 28.0 (Zr₈₅Ni₁₅). In addition, the ratio of the pumping speed of water vapor to that of hydrogen at room temperature varied with alloying element : for example, 1/40 for Zr₅₇V₃₆Fe₇ and 1/4 for Zr₆₇Ni₃₃. The alloying effects mentioned above are considered due to modification of the electronic and/or geometric structure of Zr with alloying.

Kuniaki Watanabe, Kenji Ichimura, Kan Ashida, Masao Matsuyama, Toyosaburo Takeuchi

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

Abstract

    Activation process and absorption/desorption of hydrogen isotopes were studied for Zr-Ni alloys by means of XPS-SIMS thermal desorption spectroscopy. Alloying of Ni to Zr gave rise to considerable modification of the getter properties: it caused the change in the activation temperature, the activation energy for hydrogen absorption, the heat of absorption, selective pumping property, and the kinetic isotope effect. The results indicate that one can develop Zr-Ni getters applicable to the various unit processes in the fuel handling systems of thermonuclear reactors.

Hitoshi Miyake^a, Masao Matsuyama^a, Kuniaki Watanabe^a, Kemetaro Kaneko^b, Yoichi Kobayashi^c

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

^bAccelerator Research Division, Institute for Nuclear Study, University of Tokyo, Midoricho 3-2-1, Tanashi 188, Japan

^c MKS Japan, Inc., Yotsuya 4-28, Shinjuku, Tokyo 160, Japan