N. Azuma^a, T. Miyazaki^a, K. Fueki^a, K. Ashida^b, K. Watanabe^b, K. Furukawa^c, S. Ohno^c

^a Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Chikusa-ku, Nagoya 464, Japan

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

^c Department of Chemistry, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-11, Japan

Abstract

    When silica is irradiated by 80-keV D⁺ ions or RF plasma of D₂ gas, deuterium is trapped in the silica forming Si-OD bonds. The deuterium, trapped as OD bonds, is desorbed from the silica upon heating to form some release products. The thermal detrapping process corresponds to decrease of OD bonds and was studied by measurement of infrared Fourier transform spectroscopy (FTIR). The release products HDO, D₂O, HD, and D₂ were measured by quadrupole mass spectroscopy (QMS). The detrapping and release processes of trapped deuterium were studied by simultaneous measurement of FTIR and QMS. Since the release spectra of HDO, D₂O, HD, and/or D₂ correspond to the decrease spectra of OD bonds, these release products are formed by thermal decomposition of OD bonds. The formation of water (HDO, D₂O) and hydrogen (HD, D₂) depends upon concentration of pre-existing OH bonds and deuterium injection methods (80-keV D⁺ implantation or RFD₂ plasma irradiation).

Keywords: D⁺ implantation; D₂ plasma; silica; thermal release

Kuniaki Watanabe, Masao Matsuyama, Kan Ashida, Hitoshi Miyake

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

Abstract

    Getter materials are promising for the research and development of thermonuclear fusion reactors from a viewpoint of tritium handling as well as fuel and impurity control in tokamaks. Some guiding rules are indispensable in developing a getter material having suitable properties for a given process in tritium handling. In analogy to the relation between the heat of oxide formation and electronegativities of elements, we studied the change in the heat of hydride formation with metals and alloys from this viewpoint: the electronegativities of getter materials and hydrogen. We found a simple relation between them in a form of (-△H_abs) = 23s (χ_M - 2.20)² + 3.72s - 3.72, where χ_M and 2.20 are the electronegativities of getter material and hydrogen, and s is the stoichiometric number of hydrogen in hydride. The standard deviation from the observed values was 〜5 kcal/mol(hydride) and/or 35%. This equation was found to be valid for 70 systems which appear to form metallic hydride. An advantage of this equation can be seen in the fact that it consists of only the electronegativities of getter materials and hydrogen, and the stoichiometric number of hydrogen, both of which can be found in literature or estimated with simple assumptions. Consequently, it will be quite useful as a guiding rule to design a getter material with a given heat of hydride (tritide) formation for metals/alloys and/or heat of hydrogen (tritium) absorption.

H. Miyake^a, K. Ichimura^a, M. Matsuyama^a, K. Ashida^a, K. Watanabe^a, S. Nakamura^b, T.Hayashi^b

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

^b ULVAC Co 2500 Hagisono, Chigasaki, Kanagawa 253, Japan

    Tritium exposure gives rise to a considerable in the noise of a mass spectrometer. To avoid this impairment and apply the mass spectrometer to D-T burning fusion devices, we developed a tritium compatible quadrupole mass spectrometer with tritium decontamination devices.
    It was observed that the noise level and width increased with tritium exposure: namely, the noise level increased to 100times of the initial one owing to cumulative tritium exposure of 0.1 Torr s. The increase in the noise width, on the other hand, was about 30 times. It was confirmed that the increase in the noises is due to the tritium adsorbed on the surfaces of the inner walls of the vacuum system, quadrupole, and detector itself: the tritium in the gas phase played only a minor role. The noise level and width could not be effectively reduced by simple evacuation at room temperature. On the other hand, it was revealed that photon irradiation by halogen lamp caused both the noise level and width to reduce. Photon irradiation by mercury lamp acted similarly. The decontamination (i.e. removal of the adsorbed tritium) is not due to a thermal effect but to photon-induced desorption. These results indicate that the tritium contamination of the mass spectrometer can be removed in-situ by photon irradiation, although an improvement of the pumping system and photon irradiation device should be required.

Masao Matsuyama^a, Hideo Nakatani^b, Kuniaki Watanabe^a

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

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

Abstract

    To measure tritium pressure in fuel processing system in D-T burning fusion devices, the applicability of a bremsstrahlung counting method was examined by using an apparatus for supply and recovery of highly concentrated tritium gas. For the measurement of bremsstrahlung, a newly designed proportional counter showed a considerably high sensitivity to the measurement of bremsstrahlung. In addition, the bremsstrahlung counting rate showed excellent linearity to tritium partial pressure when the total pressure was below 100 Torr. Above this upper pressure limit, the counting rate deviated downward from the linear relation. The deviation, however, could be represented quite well by a simple exponential function of pressure. It was shown that the tritium partial pressure in the hydrogen isotope gases could be determined in the range from 5×10^-2 to 760 Torr. Consequently, the present methods is quite useful for in-situ and non-destructive measurements of tritium partial pressure in the fuel processing systems of thermo-nuclear fusion devices.

Hitoshi Miyake, Masao Matsuyama, Kuniaki Watanabe

Abstract

    The feasibility of conventional mass spectrometers is seriously impaired by tritium ad/absorbed on/in the component materials (contamination) owing to β-rays from the contaminant. We developed a quadrupole mass spectrometer coupled with tritium decontamination devices consisting of mercury and deuterium lamps. In addition, their relevant parts were coated with gold. By using this apparatus, we measured the increase in the noise level and fluctuation of the base line (noise width) of the mass spectrometer owing to tritium exposure and decontamination efficiency of photon irradiation. It was observed that the rate of increase in the noise level and width with exposure to tritiated water considerably faster than that to the same amount of tritium gas, indicating tritiated water being absorbed more readily than tritium gas on the surfaces of gold coated component materials. The extent of the contamination, however, was considerably smaller than conventional mass spectrometers without gold coating. In addition, the decontamination by photon irradiation was considerably effective. The results indicate that the newly developed mass spectrometer is useful for large scale tritium handling systems such as thermonuclear fusion devices as well as laboratory experiments.

K. Ashida, H. Miyake, M. Matsuyama, K. Watanabe

Abstract

    The leak tightness, which is of serious concern with the safe handing of a large amount of tritium, of three vacuum joints (ICF-70, V24 and 1/2”-Swagelok) was examined with a newly designed equipment using tritium as probe gas. The equipment was a system made of stainless steel tubes (1/2” in diameter) connected to a vacuum system. Other ends of the tubes were connected to the test joints, the counter sides of which were put on the lid with respective coupler joints. Each test joint was enclosed with an container made of stainless steel. Tritium leaked from the seals to respective containers was measured with an ionization chamber. The detection limit of this method depends on the pressure or concentration of loaded tritium, sensitivity of the ionization chamber and time of accumulation of leaked tritium. For example, it was evaluated as 2.5×10^-12 and 1.0×10^-14 Torr. l(HT)/s for the accumulation times of 10 min and 40 hrs, respectively, at a pressure (P_HT) of 0.33 Torr. The leak rates from the ICF-70 and Swagelok were below 10^-14 Torr. l(HT)/s at room temperature. On the other hand, the leak from V24 was considerably fast: the leak rate constant was 1.44×10^-11 l/s. It was due to the permeation through the viton-0-ring. The apparent diffusion constant (D), permeation constant (KD) and solubility (K) at room temperature were evaluated as 2.2×10^-6 cm²/s, 3.0×10^-9 cm²/s, and 1.4×10^-3, respectively.

Isao Kanesaka^a, Hideyuki Takahashi^a, Hiroyuki Nishimura^a, Kiyoyasu Kawai^a, Kuniaki Watanabe^b

^aFaculty of Science, Toyama University, Gofuku, Toyama 930

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

Abstract

    β-radiolysis in a methanol-T₂O system in a gaseous state was studied by means of infrared spectroscopy over a period of 10 months. Slow formation of CH₂TOH was found. The main product was CO, with small amounts of CH₄, HCO₂CH₃, CH₂(OCH₃)₂ and (CH₃)₂O; ethylene glycol and H₂CO were not found. This result, which is quite different from that or γ-radiolysis, is explained in terms of surface reactions on stainless steel.

Keywords: IR; methanol/Radiolysis; methanol/Tritium; methanol/G value; methanol by T/Kinetics; decomposition of methanol/Methanol; radiolysis by T