Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Cantarel, V.; Lambertin, D.*; Labed, V.*; Yamagishi, Isao
Journal of Nuclear Science and Technology, 58(1), p.62 - 71, 2021/01
Times Cited Count：3 Percentile：44.39(Nuclear Science & Technology)The gas production of wasteforms is a major safety concern for encapsulating active nuclear wastes. For geopolymers and cements, the H
produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the gas composition evolution around geopolymers was monitored on line under 
Co gamma irradiation. Transient evolution of the hydrogen production yield was measured for samples with different formulations. The rate of its evolution and the final values are consistent with the presence of a chemical reaction of the pseudo-first order consuming hydrogen in the samples. The results show this phenomenon can significantly reduce the hydrogen source term of geopolymer wasteform provided their diffusion constant remains low. Lower hydrogen production rates and faster kinetics were observed with geopolymers formulations in which pore water pH was higher. Besides hydrogen production, a steady oxygen consumption was observed for all geopolymers samples. The oxygen consumption rates are proportional to the diffusion constants estimated in the modelization of hydrogen recombination by a pseudo first order reaction.
Hamamoto, Takafumi*; Ishida, Keisuke*; Shibutani, Sanae*; Fujisaki, Kiyoshi*; Tachi, Yukio; Ishiguro, Katsuhiko*; McKinley, I. G.*
Proceedings of 2019 International High-Level Radioactive Waste Management Conference (IHLRWM 2019) (USB Flash Drive), p.77 - 82, 2019/04
Iwai, Yasunori
Fusion Engineering and Design, 98-99, p.1796 - 1799, 2015/10
Times Cited Count：5 Percentile：42.01(Nuclear Science & Technology)Hydrophobic platinum catalysts have been widely applied in the field of nuclear fusion for the exchange reactions of hydrogen isotopes between hydrogen and vapor in the water detritiation system, and for the oxidation of tritium on the atmospheric detritiation system. Hydrophobic platinum catalysts are hardly susceptible to water mist and water vapor. Hydrophobic platinum catalysts are produced by supporting platinum directly on hydrophobic polymer beads. For the hydrophobic polymer, styrene - divinyl benzene (SDB) has been applied in Japan. It can be pointed out that the upgrade in catalytic activity of hydrophobic catalyst is expected to downsize the catalytic reactor based on a hard look at a large increase in flow rate in future. The upgrade in catalytic activity of two types of commercial Pt/SDB catalysts was found when they were irradiated with electron beams. After irradiation with electron beams, the catalytic activity was evaluated by means of overall reaction rate constant for the oxidation of tritium. The overall reaction rate constant increased as increase in dose. The constant showed the peak value in the dose between 500 to 1000 kGy. After the peak, the constant decreased as increase in dose. The overall reaction rate constant at the peak was 6 times larger than that evaluated with unirradiated. The mechanical strength of irradiated Pt/SDB kept sound until 1500 kGy. The irradiation is a promising method to the upgrading in catalytic activity of Pt/SDB catalyst.
Nakahira, Masataka; Takeda, Nobukazu
Hozengaku, 4(4), p.47 - 52, 2006/01
The technical structural standard for ITER (International Thermonuclear Experimental Fusion Reactor) should be innovative because of their quite different features of safety and mechanical components from nuclear fission reactors, and the necessity of introducing several new fabrication and examination technologies. Recognizing the international importance of Fusion Standard, Japan and ASME has started the cooperation development of the Fusion Standard. This paper shows the special features of ITER from view points of safety, design and fabrication, and proposes approach for development of the fusion standard.
Nakahira, Masataka
JAERI-Research 2005-030, 182 Pages, 2005/09
JAERI-Research-2005-030.pdf:12.57MB
It is difficult for Vacuum Vessel (VV) of ITER to apply a non-destructive in-service inspection (ISI) and then new safety concept is needed. Present fabrication standards are not applicable to the VV, because the access is limited to the backside of closure weld of double wall. Fabrication tolerance of VV is 
5mm even the structure is huge as high as 10m. This accuracy requires a rational method on the estimation of welding deformation. In this report, an inherent safety feature of the tokamak is proved closing up a special characteristic of termination of fusion reaction due to tiny water leak. A rational concept not to require ISI without sacrificing safety is shown based on this result. A partial penetration T-welded joint is proposed to establish a rational fabrication method of double wall. Strength and susceptibility to crevice corrosion is evaluated for this joint and feasibility is confirmed. A rational method of estimation of welding deformation for large and complex structure is proposed and the efficiency is shown by comparing analysis experimental results of full-scale test.
Nakahira, Masataka; Shibui, Masanao*
Nihon Kikai Gakkai Dai-9-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, No.04-2, p.267 - 272, 2004/06
A small water leak can cause a plasma disruption in a tokamak-type fusion machine. This plasma disruption will induce electromagnetic (EM) force acting in the vacuum vessel that is a physical barrier of tritium and activated dust. If the VV can sustain an unstable fracture by the EM force, the structural safety will be assured and the inherent safety will be demonstrated. Therefore, a new analytical model to evaluate the through crack and leak rate of cooling water is proposed, with verification by experimental leak measurements. Based on the analysis, the critical crack length to terminate plasma in ITER is evaluated as about 2 mm. On the other hand, the critical crack length for unstable fracture is obtained as about 400 mm. It is concluded that EM forces induced by the small leak to terminate plasma will not cause unstable fracture of the VV; thus the inherent safety is demonstrated.
Nishitani, Takeo; Ochiai, Kentaro; Yoshida, Shigeo*; Tanaka, Ryohei*; Wakisaka, Masashi*; Nakao, Makoto*; Sato, Satoshi; Yamauchi, Michinori*; Hori, Junichi; Wada, Masayuki*; et al.
Journal of Nuclear Science and Technology, 41(Suppl.4), p.58 - 61, 2004/03
no abstracts in English
Nakahira, Masataka
Journal of Nuclear Science and Technology, 41(2), p.226 - 234, 2004/02
Times Cited Count：1 Percentile：10.2(Nuclear Science & Technology)A tokamak-type fusion machine is said to have inherent safety associated with plasma shutdown. A small leak of water can terminate the plasma safely and can cause a plasma disruption which will induce electromagnetic(EM) forces in the vacuum vessel (VV). From a radiological safety view point, the VV forms the physical barrier that encloses tritium and activated dust. If the VV can sustain an unstable fracture by EM forces from a through crack to cause the leak, the structural safety will be assured and the inherent safety will be demonstrated. Therefore, a systematic approach to assure the structural safety is developed. A new analytical model to evaluate the through crack and leak is proposed, with verification by experiment. Based on the analyses, the critical crack length to terminate plasma is evaluated as about 2 mm, and the critical crack length for unstable fracture is obtained as about 400 mm. It is therefore concluded that EM forces induced by small leak to terminate plasma will not cause the unstable fracture of VV, and then the inherent safety is demonstrated.
Nakahira, Masataka
JAERI-Tech 2003-087, 28 Pages, 2003/12
JAERI-Tech-2003-087.pdf:1.74MB
A tokamak-type fusion machine has been characterized as having inherent plasma shutdown safety. An extremely small leakage of cooling water will cause a plasma disruption. This plasma disruption will induce electromagnetic forces (EM forces) acting in the vacuum vessel (VV) which forms the physical barrier enclosing tritium and activated dust. If the VV has the possibility of sustaining an unstable fracture from a penetrating crack caused by EM forces, the structural safety will be assured and the inherent safety will be demonstrated. This paper analytically assures the Leak-Before-Break (LBB) concept as applied to the VV and is based on experimental leak rate data of a through crack having a very small opening. Based on the analysis, the critical crack length to terminate plasma is evaluated as about 2 mm. On the other hand, the critical crack length for unstable fracture is obtained as about 400 mm. It is therefore concluded that EM forces induced by small leak to terminate plasma will not cause the unstable fracture of VV, and then the inherent safety is demonstrated.
Tada, Eisuke; Hada, Kazuhiko; Maruo, Takeshi; Safety Design/Evaluation Group
Purazuma, Kaku Yugo Gakkai-Shi, 78(11), p.1145 - 1156, 2002/11
no abstracts in English
Nishi, Masataka; Hayashi, Takumi; Shu, Wataru; Nakamura, Hirofumi; Kawamura, Yoshinori; Yamada, Masayuki; Suzuki, Takumi; Iwai, Yasunori; Kobayashi, Kazuhiro; Isobe, Kanetsugu; et al.
Materialovedenie (Russian Science of Materials) No.2, p.42 - 45, 2002/00
no abstracts in English
Gulden, W.*; Cook, I.*; Marbach, G.*; Raeder, J.*; Petti, D.*; Seki, Yasushi
Fusion Engineering and Design, 51-52(Part.B), p.419 - 427, 2000/11
Times Cited Count：5 Percentile：37.97(Nuclear Science & Technology)no abstracts in English
Maekawa, Fujio; Ikeda, Yujiro
Fusion Engineering and Design, 47(4), p.377 - 388, 2000/01
Times Cited Count：12 Percentile：60.3(Nuclear Science & Technology)no abstracts in English
N.P.Taylor*; Ikeda, Yujiro; Bartels, H.-W.*; G.Cambi*; D.G.Ceprage*; E.T.Cheng*; R.A.Forrest*; H.Iida*; H.Y.Khater*; Maekawa, Fujio; et al.
Fusion Engineering and Design, 45(1), p.75 - 88, 1999/00
Times Cited Count：8 Percentile：54.16(Nuclear Science & Technology)no abstracts in English
Seki, Yasushi; Kurihara, Ryoichi; Nishio, Satoshi; Ueda, Shuzo; Aoki, Isao; Ajima, Toshio*; Kunugi, Tomoaki; Takase, Kazuyuki; Shibata, Mitsuhiko
Fusion Engineering and Design, 42(1-4), p.37 - 44, 1998/09
Times Cited Count：1 Percentile：15.16(Nuclear Science & Technology)no abstracts in English
Seki, Yasushi
Purazuma, Kaku Yugo Gakkai-Shi, 74(9), p.939 - 943, 1998/09
no abstracts in English
Seki, Yasushi
Purazuma, Kaku Yugo Gakkai-Shi, 74(8), p.795 - 801, 1998/08
no abstracts in English
Inabe, Teruo; Seki, Masahiro; Tsunematsu, Toshihide
Fusion Engineering and Design, 42, p.7 - 12, 1998/00
Times Cited Count：4 Percentile：39.02(Nuclear Science & Technology)no abstracts in English
Takase, Kazuyuki; Kunugi, Tomoaki
Purazuma, Kaku Yugo Gakkai-Shi, 73(8), p.781 - 785, 1997/08
no abstracts in English
Kunugi, Tomoaki; Takase, Kazuyuki; Ogawa, Masuro; Seki, Yasushi
16th IEEE/NPSS Symp. on Fusion Engineering (SOFE '95), 1, p.313 - 316, 1996/00
no abstracts in English
