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Katsumi, Toshiyuki*; Zemba, Atsushi*; Kogishi, Makoto*; Iwanaga, Kohei*; Abe, Satoshi; Di
vart, P.*; Chaumeix, N.*; Kadowaki, Satoshi*
Journal of Thermal Science and Technology (Internet), 20(1), p.25-00103_1 - 25-00103_13, 2025/06
Times Cited Count：0 Percentile：0.00(Thermodynamics)In the serious accident at Fukushima Daiichi Nuclear Power Station, the presence of steam together with flammable organic compounds affected the hydrogen explosion. To investigate the effects of addition of inert gas, i.e. steam or nitrogen, on the explosion characteristics, we conducted the experiments of spherically expanding hydrogen-methane-air premixed flames in closed combustion vessels. Two types of vessels were used, and expanding flames were caught by Schlieren method. The flame propagation velocity depending on the flame radius was obtained by analyzing Schlieren images. When the flame radius was sufficiently small, smooth surface was found. The addition of inert gas to hydrogen-methane-air premixtures caused the decrease of propagation velocity of unstretched flame. When the flame radius was large, on the other hand, cellular surface generated by intrinsic instability was found. In this range, the flame acceleration was confirmed, which was induced by the evolution of cellular surface. We obtained the parameters of flame acceleration model and predicted the flame propagation velocity depending on the flame radius. The increment coefficient normalized by the propagation velocity of unstretched flame became larger at low equivalence ratios, which was due to stronger diffusive-thermal instability. Under the same equivalence ratio, the inert gas addition caused the increase of normalized increment coefficient. This denoted that the inert gas addition promoted the instability of premixed flames, which was due to the reduction of the effective Lewis number. The maximum pressure in a combustion vessel became lower in the case of inert gas addition. Moreover, the maximum pressure of experiments was lower than that of calculations under the adiabatic conditions, because of heat loss during premixed combustion. The obtained results were valuable knowledge to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station.
Watanabe, Kazuhiro; Yamanaka, Haruhiko; Maejima, Tetsuya; Inoue, Takashi; Hanada, Masaya; Tanaka, Shigeru*; Kadowaki, Makoto*
no journal, ,
A DC -1 MV insulation transformer is required for ITER NBI power supply. However such insulation transformer has not been developed. Demonstration of the DC ultra high voltage insulation is essential to realize such insulation transformer. To demonstrate the insulation transformer, a transformer model has been designed and fabricated under the ITER research and development task. The high voltage test with the model has been successfully performed and it ensures that the real insulation transformer can be fabricated.
Tobari, Hiroyuki; Hanada, Masaya; Watanabe, Kazuhiro; Kashiwagi, Mieko; Kojima, Atsushi; Dairaku, Masayuki; Seki, Norikatsu; Abe, Hiroyuki; Umeda, Naotaka; Yamanaka, Haruhiko; et al.
no journal, ,
Progress on technical development on ITER and JT-60SA neutral beam injector (NBI) were reported. In development of a 1 MV insulating transformer for ITER NB power supply, a bushing extracting 1 MV required a huge insulator that was impossible to manufacture. To solve this issue, a composite bushing with FRP tube and a small condenser bushing with insulation gas was newly developed. In development the HV bushing as an insulating feed through, voltage holding in large cylindrical electrodes inside the HV bushing was investigated. The scaling for vacuum insulation design of large cylindrical electrodes was obtained. Toward long pulse production and acceleration of negative ion beam, active control system of plasma grid temperature and a new extractor consisting of the extraction grid with high water cooling capability and aperture offset were developed. As a result, 15 negative ion beam has been achieved for 100 s. Also beam energy density has been increased two orders of magnitude.
Watanabe, Kazuhiro; Yamanaka, Haruhiko; Yamaguchi, Kohei*; Kadowaki, Makoto*; Ichimura, Satoshi*
no journal, ,
An insulation transformer for ITER Project is required to supply AC power source for ion source and extractor power supplies located on DC -1 MV insulated deck. A mockup model for the insulation transformer has been developed to verify the insulation capability of DC -1 MV and assembling procedure. It has been successfully demonstrated for sufficient insulation of higher than DC -1 MV through dielectric tests.
