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Journal Articles

Deuterium permeation behavior for damaged tungsten by ion implantation

Oya, Yasuhisa*; Li, X.*; Sato, Misaki*; Yuyama, Kenta*; Oyaizu, Makoto; Hayashi, Takumi; Yamanishi, Toshihiko; Okuno, Kenji*

Journal of Nuclear Science and Technology, 53(3), p.402 - 405, 2016/03

 Times Cited Count:10 Percentile:78.98(Nuclear Science & Technology)

The deuterium (D) permeation behaviors for ion damaged tungsten (W) by 3 keV D$$_{2}$$$$^{+}$$ and 10 keV C$$^{+}$$ were studied. The D permeability was obtained for un-damaged W at various temperatures. For both D$$_{2}$$$$^{+}$$ and C$$^{+}$$ implanted W, the permeability was clearly reduced. But, for the D$$_{2}$$$$^{+}$$ implanted W, the permeability was recovered by heating at 1173 K and it was almost consistent with that for un-damaged W. In the case of C$$^{+}$$ implanted W, the permeability was not recovered even if the sample was heated at 1173 K, indicating that the existence of carbon would prevent the recovery of permeation path in W. In addition, TEM observation showed the voids were grown by heating at 1173 K and not removed, showing the existence of damages would not largely influence on the hydrogen permeation behavior in W in the present study.

Journal Articles

Effect of neutron energy and fluence on deuterium retention behaviour in neutron irradiated tungsten

Fujita, Hiroe*; Yuyama, Kenta*; Li, X.*; Hatano, Yuji*; Toyama, Takeshi*; Ota, Masayuki; Ochiai, Kentaro; Yoshida, Naoaki*; Chikada, Takumi*; Oya, Yasuhisa*

Physica Scripta, 2016(T167), p.014068_1 - 014068_5, 2016/02

 Times Cited Count:25 Percentile:83.87(Physics, Multidisciplinary)

The irradiation defects were introduced by Fe$$^{2+}$$ irradiation, fission neutron irradiation and D-T neutron irradiation. After the irradiation, the deuterium ions (D$$_{2}^{+}$$) implantation was performed and the D retention behavior was evaluated by thermal desorption spectroscopy. The experimental results indicated that dense vacancies and voids within the shallow region near the surface were introduced by Fe$$^{2+}$$ irradiation. The trapping state of D by vacancies and void were clearly controlled by the damage concentration and the voids would become the most stable D trapping site. For fission neutron irradiated W, most of the D was adsorbed on the surface and/or trapped by dislocation loops and no vacancies and voids for D trapping due to its lower damage concentration. D trapping by vacancies were found in the bulk of D-T neutron irradiated W, indicating that the neutron energy distribution could make a large impact on irradiation defect formation and the D retention behavior.

Journal Articles

Hydrogen isotope behavior on a water-metal boundary with simultaneous transfer from and to the metal surface

Hayashi, Takumi; Isobe, Kanetsugu; Nakamura, Hirofumi; Kobayashi, Kazuhiro; Oya, Yasuhisa*; Okuno, Kenji*; Oyaizu, Makoto; Edao, Yuki; Yamanishi, Toshihiko

Fusion Engineering and Design, 89(7-8), p.1520 - 1523, 2014/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Tritium confinement is the most important safety issue in the fusion reactor. Tritium behavior on the water metal boundary is very important to design tritium plant with breading blanket system using cooling water. A series of tritium permeation experiment into pressurized water or water vapor jacket with He or Ar have been performed through pure iron piping with/without 7 micro-meter gold plating, which contained about 1 kPa of pure tritium gas at 423 K, with monitoring the chemical forms of tritium. Also, deuterium permeation experiments from heavy water vessel through various metal piping, such as pure iron (Fe), nickel (Ni), stainless steel (SS304), and pure iron with 10 micro-meter gold plating, were performed at 573 K and at 15 MPa. Recently, using the above heavy water system, we have succeeded to detect simultaneous hydrogen isotopes transfer from and to the metal surface by introducing H$$_{2}$$ gas to the metal piping after stabilized deuterium permeation was detected.

Journal Articles

Hydrogen isotope permeation from cooling water through various metal piping

Hayashi, Takumi; Nakamura, Hirofumi; Isobe, Kanetsugu; Kobayashi, Kazuhiro; Oyaizu, Makoto; Yamanishi, Toshihiko; Oya, Yasuhisa*; Okuno, Kenji*

Fusion Engineering and Design, 87(7-8), p.1333 - 1337, 2012/08

 Times Cited Count:7 Percentile:53.66(Nuclear Science & Technology)

In order to investigate the behavior of hydrogen isotope on the water-metal boundary, deuterium permeation experiments from heavy water vessel through various metal piping, such as pure iron (Fe), nickel (Ni), stainless steel (SS304), and pure iron with 10 $$mu$$m gold plating, were performed at 573 K and at 15 MPa. During the experiment, surfaces of metal piping except gold plating one were oxidized at the heavy water boundary and then deuterium would generate by the oxidation reactions. This deuterium could be detected by mass spectrometer, which monitored the inside gases of the piping under vacuum. The result showed clearly that the deuterium permeated through Fe, Ni, and SS304 piping was detected as deuterium gas (D$$_{2}$$) under vacuum, though that through gold plating one could not be detected effectively. The D$$_{2}$$ permeation rate through Fe, Ni, and SS304 piping reached some stabilized value. This paper summarizes the above experimental results and discusses the mechanism of deuterium behavior on the water metal boundary.

Journal Articles

Hydrogen isotope behavior transferring through water metal boundary

Hayashi, Takumi; Nakamura, Hirofumi; Isobe, Kanetsugu; Kobayashi, Kazuhiro; Oyaizu, Makoto; Oya, Yasuhisa*; Okuno, Kenji*; Yamanishi, Toshihiko

Fusion Science and Technology, 60(1), p.369 - 372, 2011/07

 Times Cited Count:2 Percentile:20.43(Nuclear Science & Technology)

Journal Articles

Dynamic behaviors of deuterium retained in SS-316 oxidized at various temperatures

Kobayashi, Makoto*; Wang, W.*; Kurata, Rie; Matsuyama, Masao*; Hayashi, Takumi; Yamanishi, Toshihiko; Asakura, Yamato*; Oya, Yasuhisa*; Okuno, Kenji*

Fusion Science and Technology, 60(1), p.403 - 406, 2011/07

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The trapping and release mechanisms of hydrogen isotopes for the stainless steel (SS) oxidized at various temperatures were investigated. The oxide layer was mainly consisted of iron oxides (Fe$$_{x}$$O$$_{y}$$) and its decomposition temperature was almost consistent with the release temperature of deuterium, where major chemical form was a molecular deuterium (D$$_{2}$$). The deuterium retention was increased as the oxidation temperature increased. It was considered that the thickness of oxide layer would make a large influence on the retention of hydrogen isotopes. On the other hand, the amount of released deuterium as heavy water (D$$_{2}$$O) was independent with oxidation temperature. It was considered that the formation of hydrogen isotope as water form was depended on the amount of Fe$$_{x}$$O$$_{y}$$ on the top most surface layer of SS.

Journal Articles

Function of water molecule for tritium behavior on the water-metal boundary

Hayashi, Takumi; Nakamura, Hirofumi; Isobe, Kanetsugu; Kobayashi, Kazuhiro; Oyaizu, Makoto; Yamanishi, Toshihiko; Ishikawa, Hirotada*; Oya, Yasuhisa*; Okuno, Kenji*

Fusion Science and Technology, 56(2), p.836 - 840, 2009/08

 Times Cited Count:11 Percentile:63.13(Nuclear Science & Technology)

Journal Articles

Hydrogen retention and carbon deposition in plasma facing components and the shadowed area of JT-60U

Masaki, Kei; Tanabe, Tetsuo*; Hirohata, Yuko*; Oya, Yasuhisa*; Shibahara, Takahiro*; Hayashi, Takao; Sugiyama, Kazuyoshi*; Arai, Takashi; Okuno, Kenji*; Miya, Naoyuki

Nuclear Fusion, 47(11), p.1577 - 1582, 2007/11

 Times Cited Count:14 Percentile:48.36(Physics, Fluids & Plasmas)

In JT-60U, erosion/deposition analyses for the plasma facing wall have shown that deposition was dominant at the inner-middle first wall and the inner divertor, whereas erosion dominant at the upper first wall and the outer divertor. Assuming toroidal symmetry in the erosion and deposition patterns, the net carbon erosion and deposition in the divertor area were estimated to be 0.34 kg and 0.55 kg, respectively. In a whole, the increment of carbon in the divertor region was 0.21 kg, which should be originated from the first wall. The hydrogen concentration in the thick deposition layer of the inner divertor was 0.02 in (H+D)/C. In the plasma-shadowed area underneath the divertor region at around 420 K, re-deposited layers of 2 $$mu$$m-thick were found with high hydrogen concentration of 0.8 in (H+D)/C. The carbon deposition rate in the plasma-shadowed area, however, was 8$$times$$10$$^{19}$$ atoms/s, which was one order smaller than that (6$$times$$10$$^{20}$$ atoms/s) on the wall surface.

Journal Articles

Study for the behavior of tritiated water vapor on organic materials

Kobayashi, Kazuhiro; Hayashi, Takumi; Nakamura, Hirofumi; Yamanishi, Toshihiko; Oya, Yasuhisa*; Okuno, Kenji*

Fusion Science and Technology, 52(3), p.696 - 700, 2007/10

 Times Cited Count:1 Percentile:11.92(Nuclear Science & Technology)

In a fusion reactor of high safety and acceptability, safe confinement of tritium is one of key issues for the fusion reactor. Tritium should be well-controlled and not excessively released to the environment and to prevent workers from excess exposure. Especially, the hot cell and tritium facilities of ITER will use various construction materials. For tritium decontamination processes, so-called soaking effect is important. This effect is based on sorption of tritiated water vapor on the materials and subsequent desorption from them. Therefore, in order to develop for the optimal decontamination technique, the decontamination experiment was carried out as a function of water vapor concentration in the purging gas for epoxy paint, acrylic resin and butyl rubber. As the result, about 70% of the adsorbed tritium on the epoxy paint was removed by adding water vapor in purging gas for 12 hrs. The effect of adding water vapor was found on the decontamination for epoxy paint.

Journal Articles

Hydrogen isotope retentions and erosion/deposition profiles in the first wall of JT-60U

Oya, Yasuhisa*; Hirohata, Yuko*; Nakahata, Toshihiko*; Suda, Taichi*; Yoshida, Masashi*; Arai, Takashi; Masaki, Kei; Okuno, Kenji*; Tanabe, Tetsuo*

Fusion Science and Technology, 52(3), p.554 - 558, 2007/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

To investigate retention characteristics of hydrogen isotopes in the first wall tiles of JT-60U, surface morphology, erosion/deposition profiles and hydrogen isotope retentions were examined by SEM, XPS, TDS and SIMS. It was found that poloidal deuterium retention profile was rather uniform, while the thermal desorption behavior of deuterium was quite different depending on the locations of the tiles. Deuterium retained in the upper first wall, where was covered by thick boron layers with high concentration of B, was desorbed at lower temperature than that in the lower area covered by carbon layers with much less B content. D/H ratio in the first wall tiles was appreciably higher than that observed in the divertor tiles, suggesting the injection of high energy deuteron originating from NBI into the first wall. In addition, the lower temperature of the first wall compared to that of the divertor tiles would prohibit desorption of the implanted deuterium and/or its replacement by subsequent D or H impingement.

Journal Articles

Dynamics of deuterium implanted in boron coating film for wall conditioning

Nakahata, Toshihiko*; Yoshikawa, Akira*; Oyaizu, Makoto*; Oya, Yasuhisa*; Ishimoto, Yuki*; Kizu, Kaname; Yagyu, Junichi; Ashikawa, Naoko*; Nishimura, Kiyohiko*; Miya, Naoyuki; et al.

Journal of Nuclear Materials, 367-370(2), p.1170 - 1174, 2007/08

 Times Cited Count:2 Percentile:19.85(Materials Science, Multidisciplinary)

Retention and desorption behavior of deuterium implanted into pure boron films has been studied by means of the secondary ion mass spectroscopy. It was found that the factor dominating deuterium desorption was the sample temperature. At stage 1, below 573 K, the desorption of deuterium from B-D-B bond dominated and diffusion was the rate-determining process in this stage. Above 573 K, deuterium was mainly desorbed from B-D bonds, and recombination was the rate-determining process in this stage. The effective molecular recombination rate constant of deuterium trapped as B-D bond was determined by an isothermal annealing experiment.

Journal Articles

Hydrogen isotopes retention in JT-60U

Hirohata, Yuko*; Tanabe, Tetsuo*; Oya, Yasuhisa*; Okuno, Kenji*; Masaki, Kei; Miya, Naoyuki; JT-60U Team

Journal of Nuclear Materials, 363-365, p.854 - 861, 2007/06

 Times Cited Count:11 Percentile:63.76(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Comparison of boronized wall in LHD and JT-60U

Ashikawa, Naoko*; Kizu, Kaname; Yagyu, Junichi; Nakahata, Toshihiko*; Nobuta, Yuji; Nishimura, Kiyohiko*; Yoshikawa, Akira*; Ishimoto, Yuki*; Oya, Yasuhisa*; Okuno, Kenji*; et al.

Journal of Nuclear Materials, 363-365, p.1352 - 1357, 2007/06

 Times Cited Count:9 Percentile:57.83(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Hydrogen retention and carbon deposition in plasma facing wall and shadowed area of JT-60U

Masaki, Kei; Tanabe, Tetsuo*; Hirohata, Yuko*; Oya, Yasuhisa*; Shibahara, Takahiro*; Hayashi, Takao; Sugiyama, Kazuyoshi*; Arai, Takashi; Okuno, Kenji*; Miya, Naoyuki

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Evaluation of fuel inventory and its retention process are critical issues for a next-step fusion device, especially with carbon-based wall. In order to resolve the issues, the hydrogen retention and carbon deposition analyses for the plasma facing surfaces and plasma-shadowed area of JT-60U have been performed. In JT-60U, erosion/deposition analyses for the plasma facing wall have shown that deposition was dominant at the inner-middle first wall and the inner divertor, whereas erosion dominant at the upper first wall and the outer divertor. Assuming toroidal symmetry in the erosion and deposition patterns, the net carbon erosion and deposition in the divertor area were estimated to be 0.34 kg and 0.55 kg, respectively. In a whole, the increment of carbon in the divertor region was 0.21 kg, which should be originated from the first wall. The hydrogen concentration in the thick deposition layer of the inner divertor was $$sim$$0.02 in (H+D)/C. In the plasma-shadowed area underneath the divertor region at around 420 K, re-deposited layers of $$sim$$2$$mu$$m-thick were found with high hydrogen concentration of $$sim$$0.8 in (H+D)/C. The carbon deposition rate in the plasma-shadowed area, however, was 8$$times$$10$$^{19}$$ atoms/s, which was one order smaller than that (6$$times$$10$$^{20}$$ atoms/s) on the wall surface.

Journal Articles

Hydrogen isotope retention of JT-60U W-shaped divertor tiles exposed to DD discharges

Shibahara, Takahiro*; Tanabe, Tetsuo*; Hirohata, Yuko*; Oya, Yasuhisa*; Oyaizu, Makoto*; Yoshikawa, Akira*; Onishi, Yoshihiro*; Arai, Takashi; Masaki, Kei; Okuno, Kenji*; et al.

Journal of Nuclear Materials, 357(1-3), p.115 - 125, 2006/10

 Times Cited Count:20 Percentile:81.23(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Hydrogen retention of JT-60 open divertor tiles exposed to HH discharges

Shibahara, Takahiro*; Tanabe, Tetsuo*; Hirohata, Yuko*; Oya, Yasuhisa*; Oyaizu, Makoto*; Yoshikawa, Akira*; Onishi, Yoshihiro*; Arai, Takashi; Masaki, Kei; Okuno, Kenji*; et al.

Nuclear Fusion, 46(10), p.841 - 847, 2006/10

 Times Cited Count:17 Percentile:53.06(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Sorption and desorption of tritiated water on four kinds of materials for ITER

Kobayashi, Kazuhiro; Hayashi, Takumi; Nishi, Masataka; Oya, Yasuhisa*; Okuno, Kenji*

Fusion Engineering and Design, 81(8-14), p.1379 - 1384, 2006/02

 Times Cited Count:5 Percentile:38.34(Nuclear Science & Technology)

In facilities of ITER, various construction materials are possibly exposed by tritium during periodical maintenances and an accident. It is required to establish the effective surface decontamination methods for the above construction materials of ITER. In tritium decontaminating, so-called "soaking" effect is important. This effect is based on sorption of tritiated water on the materials and subsequent desorption from them. In order to obtain and summarize data on the amount of tritium adsorption on the various materials, a series of tritiated water vapor exposure experiments have been carried out as a function of time. The amounts of tritium adsorption on the materials saturated almost within the period from several weeks to 1 month. The adsorption rate of the epoxy was found to be the largest. In the exposure time less than 2 hrs, the adsorption coefficients for the examined materials were found to be in the same order as those reported by F.Ono. It will be also discussed from viewpoint of kinetics for adsorption and desorption.

Journal Articles

Behavior on Li$$_{2}$$TiO$$_{3}$$ under varied surface condition

Olivares, R.*; Oda, Takuji*; Oya, Yasuhisa*; Tanaka, Satoru*; Tsuchiya, Kunihiko

Fusion Engineering and Design, 75-79, p.765 - 768, 2005/11

 Times Cited Count:9 Percentile:51.68(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Hydrogen isotope distributions and retentions in the inner divertor tile of JT-60U

Oya, Yasuhisa*; Hirohata, Yuko*; Tanabe, Tetsuo*; Shibahara, Takahiro*; Kimura, Hiromi*; Oyaizu, Makoto*; Arai, Takashi; Masaki, Kei; Goto, Yoshitaka*; Okuno, Kenji*; et al.

Fusion Engineering and Design, 75-79, p.945 - 949, 2005/11

 Times Cited Count:9 Percentile:55.58(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Retention of hydrogen isotopes in divertor tiles used in JT-60U

Hirohata, Yuko*; Shibahara, Takahiro*; Tanabe, Tetsuo*; Oya, Yasuhisa*; Arai, Takashi; Goto, Yoshitaka*; Masaki, Kei; Yagyu, Junichi; Oyaizu, Makoto*; Okuno, Kenji*; et al.

Fusion Science and Technology, 48(1), p.557 - 560, 2005/07

 Times Cited Count:3 Percentile:25.79(Nuclear Science & Technology)

no abstracts in English

60 (Records 1-20 displayed on this page)