Kuniaki WATANABE
Hydrogen Isotope Research Center, Toyama University,Gofuku 3190, Toyama 930-8555, JAPAN
(Received February 19, 1999; accepted March 15, 1999)

Abstract
　Research and development at the Hydrogen Isotope Research Center of Toyama University in the last nine years are briefly reviewed by focusing attention on technological developments and topics of fundamental research. This paper describes technological developments in tritium measurement by bremsstrahlung counting, tritium gettering by Zr-based alloys, gas chromatographic hydrogen isotope separation and hydrogen energy conversion by Ni-hydride battery. The topics of fundamental research are material interactions taking place on the first wall of tokamaks, isotope effects on hydrogen absorption by Pd-Pt alloys, radiochemical effects of β-rays on tritium oxidation in gas phase and internal hydride formation of Mg-Ⅲa alloys. It is pointed out that hydrogen-material interactions must be understood in more detail so as to develop new energy systems using hydrogen isotopes as fuel by nuclear fusion and chemical reactions.

Yoshiaki FUTAMURA^*, Kunihiko TSUCHIYA, Yoshiharu NAGAO, Junnya FUJITA, Hiroshi KAWAMURA
^*Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930, JAPAN
Oarai Research Establishment, Japan Atomic Energy Research Institute
3670 Shinbori, Narita-cho, Oarai-machi, Higashi-ibaraki-gun, Ibaraki-ken 311-1394, JAPAN
(Received December 15, 1998; accepted March 15, 1999)

Abstract
　To develop a tritium breeding blanket for a fusion reactor, irradiation tests in fission reactors must be conducted to obtain data on tritium production / release / recovery performance of the blanket.
  In-situ various irradiation tests have been carried out in Japan (JMTR) and Europe (HFR) to investigate tritium release characteristics from ultra-small Li₂TiO₃ pebble (1 mm dia) bed. Tritium performance irradiation tests presently focus on Li₂TiO₃ ceramic considered promising as a new strong candidate for breeding material. This report shown the present status if in-situ irradiation tests carried out throughout the world. An in-situ irradiation test program on tritium release for partial breeding blanket module is presented.

Masanori HARA, Masao MATSUYAMA, Kan ASHIDA, Yuji HATANO, W. M. SHU, Kuniaki WATANABE
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received January 22, 1999; accepted March 15, 1999)

Abstract
　A tritium experimental system for 100Ci/run was established at the Hydrogen Isotope Research Center, Toyama University. This system consisted of two distinct experimental chambers for tritium experiments and backup components such as tritium storage-supply, gas purification, isotope separation and exhaust-gas detritiation. To confirm the reliability of the detritiation device, which is an important factor of the system, the basic performance of the detritiation device was assessed using a small amount of tritium. Two different methods were examined: one is based on conventional oxidation-adsorption (wet method) and the other gettering (dry method). The wet method is advantageous if exhaust gases include large amounts of impurities such as oxygen, water, hydrocarbon and so on. The dry method is applicable for processing exhaust gases which mainly include elemental tritium with a small amount of impurities. The wet method showed excellent performance for tritium removal from exhaust gases with impurity oxygen, the initial tritium concentration was reduced below 1/10 within 20 min. Similar performance was also obtained by dry method. In addition, the absorption bed loaded with molecular sieves could be regenerated by applying the dry method. Accordingly, it was concluded that the performance of the detritiation device satisfies requirement for performing tritium experiments.

Wataru NISHIDA, Kan ASHIDA, Kuniaki WATANABE
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received January 29, 1999; accepted March 15, 1999)

Abstract
　Pd-coating of Zr-based alloys is effective for avoiding surface poisoning by impurity gases such as N2, CO2 and so on. The effectiveness of electroless Pd-coating layers over ZrNi was investigated from view points of ab/desorption kinetics of deuterium and durability toward impurity gases in Ar. The rate determining steps of deuterium absorption and desorption were not altered by Pd-coating. The absorption obeyed first order and desorption second order kinetics. Regarding the durability toward impurity gases, the Pd-coating ZrNi (Pd/ZrNi) showed much higher affinity to deuterium carried by Ar flow than bare ZrNi. The former was particularly more capable at 573K of avoiding surface poisoning. Surface modification of Zr-based alloys by Pd-coating is thus effective against impurity gases and a packed column of Pd/ZrNi is applicable to the processing of hydrogen isotopes containing impurity gases.

Tomoyasu HOSOKAWA, Masanori HARA, Kuniaki WATANABE
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received February 1, 1999; accepted March 15, 1999)

Abstract
　The recovery of hydrogen from methane by catalytic oxidation was studied over Pd/Al₂O₃ catalyst at 673 to 873K and loading concentration ratio from [O₂]/[CH₄] 0.5 to 2.0. Complete oxidation, CH₄+2O₂⇔CO₂+H₂O, took place for reactant mixtures having [O₂]/[CH₄]=1.0, irrespective of reaction temperature. Hydrogen production through partial oxidation, CH₄+1/2O₂⇔CO+2H₂, predominate throughout complete oxidation for reactant gas mixtures having [O₂]/[CH₄]≦1.0. Adsorbed species such as H_(a), O_(a), CO_(a) and OH_(a) were shown essential as reaction intermediates for both the complete and partial oxidation.

Masao MATSUYAMA, Satoshi UEDA, Takumi OGAWA, Tatsuhiko UDA^*, Kuniaki WATANABE
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
^*National Institute for Fusion Science
Oroshi 322-6, Toki 509-5292, JAPAN
(Received October 23, 1998; accepted March 15, 1999)

Abstract
　　To conduct in-situ and real-time measurements of contamination due to tritium adsorption/desorption on the surfaces and in sub-surface layers of materials, a new measuring method was established. The method is principally based on measurement of X-rays induced by β-rays from tritium. To assess the applicability of the present method, a graphite sample in which was implanted a given amount of tritium was used as a model. After tritium implantation, measurement was carried out using an ultra-low energy Ge detector under air or argon atmosphere. In the latter atmosphere, a sharp and strong characteristic X-ray peak attributed to K-transition of Ar appeared at 2.96 keV along with a broad bremsstrahlung X-ray spectrum, indicating X-rays more penetrating thanβ-rays to be effectively generated by substitution of argon and contamination to be easily evaluated by conventional X-ray detectors without special detectors for β-ray counting. Accordingly, it was revealed that the present method is valuable for in-situ and real-time measurements of surface contamination due to tritium exposure owing to high durability and reliability, simple construction and ease of maintenance.

Takuyou YASUMATSU, Masao MATSUYAMA, Kuniaki WATANAB
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received January 20, 1999; accepted March 15, 1999)

Abstract
　To obtain better working materials for recently developed gas chromatography for hydrogen isotope separation, pressure-composition-temperature relationships of hydrogen isotopes were examined for Pd-Pt and Pd-Ni alloys from 273K to 1073K at concentrations from 2x10^-4 to 0.65 in [H]/[M] ratio.
  The heat of hydride formation for the alloys decreased with increasing Pt or Ni content. The isotope effect defined as the equilibrium pressure ratio, P_D2/P_H2, did not change much with alloy composition. The equilibrium constant at infinite dilution showed strong temperature and isotope dependence. Analysis indicated the ground state of D to be 1/√2 less than that of H for respective alloys. The thermodynamic properties of hydride phase were evaluated for all the alloys and hydrogen isotopes including tritium.

Ryo HAYAKAWA, Masanori HARA^*, Toshio OKABE, Kuniaki WATANABE^*
Faculty of Science, Toyama Universit
^*Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received January 20, 1999; accepted March 15, 1999)

Abstract
　Hydrogen induced disproportionation and reproportionation of the metallic compounds, Zr₂Fe, Zr₂Co, Zr₂Ni and Zr₂Cu, were studied at 25 to 900℃ by X-ray diffraction. Zr₂Fe, Zr₂Co and Zr_2vCu formed Zr-deficient compounds and ZrHx through disproportionation reactions at room temperatures as follows

Zr₂Fe : 9Zr₂Fe + 18.5H₂ → 5Zr₃FeH₇ + 2ZrFe₂ + ZrH₂

Zr₂Co : Zr₂Co + 2.5H₂ → ZrCoH₃ + ZrH₂

Zr₂Cu : Zr₂Cu + H₂ → ZrCu + ZrH₂

           Zr₂Cu + 2.5H₂ → CuH + 2ZrH₂

Zr₂Ni formed only its hydride through

Zr₂Ni : Zr₂Ni + 2.5H₂ → Zr₂NiH₅

and did not disproportionate under the experimental conditions.
 The disproportionated Zr₂Fe and Zr₂Co reproportionated in hydrogen atmosphere at 550℃. The disproportionated Zr₂Fe and Zr₂Co did not reproportionate in hydrogen atmosphere: but only reproportionated in vacuum above 800℃.
  Differences in disproportionateon and reproportionation are considered due to relative stability of hydride and Zr-deficient intermetallic phase of the respective Zr-M systems.

Yuji HATANO, Koji KOBAYASHI^*, Katsunori MORI^*, Kuniaki WATANABE, Shotaro MOROZUMI
Hydrogen Isotope Research Center, Toyama University
^*Material Systems Engineering and Life Science, Faculty of Engineering, Toyama University
Gofuku 3190, Toyama 930-8555, JAPAN
(Received January 19, 1999; accepted March 15, 1999)

Abstract
　The influence of pre-oxidation on charge/discharge characteristics of sintered Mg₂Ni electrodes was examined with an open electrochemical cell. Mg₂Ni powder was first oxidized slightly in air at 473 K for 5-360 min and then sintered in argon atmosphere at 823 K. The cyclic stability of discharge capacity was improved markedly by pre-oxidation. Maximum cycle life was obtained using 20 min pre-oxidation. The mechanism by which pre-oxidation influences cyclic stability was examined via density measurement and surface analysis. The sintering rate had a maximum value for 20 min pre-oxidation. An MgO layer was formed on the surface of Mg₂Ni during sintering and growth rate of the MgO layer decreased with pre-oxidation. Improvement of cyclic stability with pre-oxidation was attributed to the firm aggregation between Mg₂Ni powder particles due to reduction in the thickness of MgO layer.