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Kumagai, Yuta; Nagaishi, Ryuji; Kimura, Atsushi*; Taguchi, Mitsumasa*; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.37 - 45, 2021/10
Zeolite adsorbents are to be used for decontamination of radioactive water in Fukushima Dai-ichi Nuclear Power Station. Evaluation of hydrogen production by water radiolysis during decontamination is important for safe operation. Thus hydrogen production from the mixture of zeolite adsorbents and seawater was studied because seawater was urgently used as a coolant for the fuels. The hydrogen yield from the mixture decreased at a high weight fraction of zeolites. However, the measured yield was higher than the yield expected from the direct radiolysis of seawater in the mixture, which would decrease proportional to the weight fraction of seawater. The result suggests that the radiation energy deposited to zeolites was involved in the hydrogen formation. From the results, the hydrogen production rate was evaluated to be 3.6 mL/h per ton of radioactive water before decontamination. After the process, it was evaluated to be 1.5 L/h per ton of waste adsorbents due to the high dose rate.
Nagaishi, Ryuji; Morita, Keisuke; Yamagishi, Isao; Hino, Ryutaro; Ogawa, Toru
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
Two years after Three Mile Island Unit 2 (TMI-2) loss-of-coolant accident, radioactive contaminated water has been processed by Submerged Demineralizer System (SDS) with two types of zeolite adsorbents to remove radioactive nuclides. During and after the process, adsorption amount and distribution of nuclides on the zeolites, residual water content and thermal conductivity in the SDS vessels have been measured or estimated for verification of safety in the process, subsequent transportation and disposal. Hydrogen generation has been also evaluated mainly by direct monitoring in the large-scale of vessel after the process. In this work, the revaluation of hydrogen generation was demonstrated on the basis of the open information of vessel, and the latest experimental data obtained in adsorption and radiolysis occurring in small-scale of zeolite-water mixtures. As a result, the evaluated data was found to be comparable with the reported data obtained in the large-scale of real vessel.
Suzuki, Kenji*; Yamagishi, Aoi*; Nishikawa, Satoru*; Shobu, Takahisa
Hozengaku, 11(2), p.91 - 98, 2012/07
In this study, a residual stress distribution in a dissimilar plate butt-welded joint was simulated by a thermo-elastic finite element method. The base metal was the austenitic stainless steel SUS316L. The other base metal was nickel super-alloy NCF600, and the weld metal was the alloy 82 (YNiCr-3). The dimensions of the plate butt-welded joint were a width of 200 mm, a length of 250 mm and a thickness of 25 mm. The welding joint was fabricated by TIG welding with 22 passes. For comparison, the residual stress distribution for the similar butt-welded joint of SUS316L was simulated as well as the dissimilar welded joint. According to the simulated results, there was not the difference in the thermal field between the similar and the dissimilar welded joints. The residual stress distribution in the similar welded joint became symmetrical to the welding center after removal of the weld bead. For the dissimilar welded joint, the peak of the residual stresses moved to the NCF600 side a little. The residual stress level of the dissimilar welded joint was large compared with the similar welded joint. The residual stress of the welding direction was larger than that of the transverse direction.
Kumagai, Yuta; Nagaishi, Ryuji; Kimura, Atsushi; Taguchi, Mitsumasa; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
Nihon Genshiryoku Gakkai Wabun Rombunshi, 10(4), p.235 - 239, 2011/12
Zeolite adsorbents are to be used for decontamination of radioactive water in Fukushima Dai-ichi Nuclear Power Station. Evaluation of hydrogen production by water radiolysis during decontamination is important for safe operation. Thus hydrogen production from the mixture of zeolite adsorbents and seawater was studied because seawater was urgently used as a coolant for the fuels. The hydrogen yield from the mixture decreased at a high weight fraction of zeolites. However, the measured yield was higher than the yield expected from the direct radiolysis of seawater in the mixture, which would decrease proportional to the weight fraction of seawater. The result suggests that the radiation energy deposited to zeolite is involved in the hydrogen formation. From the results, the hydrogen production rate was evaluated to be 3.6 mL/h per ton of radioactive water before decontamination. After the process, it was evaluated to be 1.5 L/h per ton of waste adsorbents due to the high dose rate.
Nakamura, Tatsuya; Tanaka, Hiroki; Yamagishi, Hideshi; Soyama, Kazuhiko; Aizawa, Kazuya; Ochi, Atsuhiko*; Tanimori, Toru*
Nuclear Instruments and Methods in Physics Research A, 573(1-2), p.187 - 190, 2007/04
Times Cited Count：9 Percentile：56.38(Instruments & Instrumentation)We have been developing a neutron imaging gas detector with a high spatial resolution and with a high temporal response for the neutron scattering instruments at the pulsed neutron source in the Japan proton accelerator research complex. The gas detector system with individual read-outs was developed to meet the requirements for the instruments for neutron reflectometry or for small angle neutron scattering. The performances of the prototype detector using a multi-wire (MW) or micro-strip (MS) detector head were evaluated using a collimated neutron beam, and we confirmed the MS detector exhibiting a spatial resolution of 1.5 mm and a pulse-pair resolution of about 100 ns with a gas pressure of 6 atm helium with a mixture of 30% CF
. The performances for the MS detector were also evaluated up to the total gas pressure of 8 atm.
Hirata, Mafumi*; Miyake, Yasuhiro*; Chujo, T.*; Kohagura, Junko*; Numakura, Tomoharu*; Shimizu, Kiyoaki*; Ito, Marie*; Kiminami, Serina*; Morimoto, Naomichi*; Hirai, Katsuaki*; et al.
Review of Scientific Instruments, 77(10), p.10E719_1 - 10E719_3, 2006/10
Times Cited Count：0 Percentile：0.01(Instruments & Instrumentation)no abstracts in English
Tanaka, Hiroki; Nakamura, Tatsuya; Yamagishi, Hideshi; Soyama, Kazuhiko; Aizawa, Kazuya; Ochi, Atsuhiko*; Tanimori, Toru*
no journal, ,
no abstracts in English
Yamagishi, Hideshi; Nakamura, Tatsuya; Tanaka, Hiroki; Soyama, Kazuhiko; Aizawa, Kazuya; Ochi, Atsuhiko*; Tanimori, Toru*
no journal, ,
no abstracts in English
Yamagishi, Hideshi; Nakamura, Tatsuya; Soyama, Kazuhiko; Aizawa, Kazuya; Tanaka, Hiroki*; Tanimori, Toru*
no journal, ,
no abstracts in English
To, Kentaro; Yamagishi, Hideshi; Soyama, Kazuhiko; Ochi, Atsuhiko*; Tanimori, Toru*
no journal, ,
Neutron scattering experiment using high intensity pulsed neutrons will be carried out in Materials and Life Science Facility at J-PARC. Several features are desired for neutron detectors in the experiments. The detectors require features such as a good spatial resolution, high detection efficiency, and fast response. In view of these requirements, we have developed a 2D position sensitive neutron detector system consist of micro-pattern detector array as detection device. In this presentation, characteristics of the 2D micro-pixel gas chamber (MPGC) under Cf-252 neutron irradiation are reported. The irradiation experiments were carried out using a mixture gas of helium and carbon tetrafluoride with total pressures of 4 and 5 atm. Signal pulse peak of neutrons can be identified and be discriminated easily from background noise generated in lower channels. Here, degradation of gas gain arisen from a charge up effect was not observed in our MPGC system.
To, Kentaro; Yamagishi, Hideshi; Soyama, Kazuhiko; Ochi, Atsuhiko*; Tanimori, Toru*
no journal, ,
Neutron scattering experiments using high intensity pulsed neutrons will be carried out in Materials and Life Science Facility at J-PARC. Detectors using in the facility require features such as a good spatial resolution, high detection efficiency, fast response, etc. We have developed a 2D position sensitive neutron detector system consist of micro-pattern detector array such as microstrip and miltiwire detector array. In this presentation, characteristics of the 2D micro-pixel gas chamber system under Cf-252 neutron irradiation are reported. Detection area used in this experiment is 50
50 mm
and pitches of both axes, anodes and cathodes, are 0.4 mm. Irradiation were carried out with a mixture gas of helium-3 and carbon tetrafluoride. It can be seen that signal pulse peaks of neutrons can be identified and these pulse peaks is discriminated easily from background noises. Here, degradation of gas gain arisen from a charge up effect was not observed in our system.
To, Kentaro; Yamagishi, Hideshi*; Sakasai, Kaoru; Nakamura, Tatsuya; Soyama, Kazuhiko; Ochi, Atsuhiko*; Tanimori, Toru*
no journal, ,
Neutron scattering experiments involving high-intensity and wide-energy pulsed neutrons are expected to be conducted at the MLF in the J-PARC. These experiments require neutron detectors with features such as a two-dimensional detection area, good spatial resolution, high detection efficiency, and a fast response time. In this study, a gas-based neutron detection system with individual readout method and consisting of a micro-pixel detector head was developed, and preliminary experiments were conducted under neutrons irradiation. To examine the operation of the detector system, the total projection ranges of the secondary particles emitted by the nuclear reaction between neutrons and 
He nuclei are measured and compared with the values obtained from a Monte Carlo simulation. Since the measured projection ranges of the secondary particles agree with the ranges obtained from the Monte Carlo simulation, it is concluded that the operation of the developed system is satisfactory.
Kumagai, Yuta; Nagaishi, Ryuji; Kimura, Atsushi; Taguchi, Mitsumasa; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
no journal, ,
For decontamination of radioactive water, zeolite is a suitable adsorbent for radioactive Cs. The management of hydrogen produced by water radiolysis is an important issue of safety. Thus hydrogen production from the mixture of mordenite-type zeolite and water was studied. In particular, we focused on the influence of the incorporation of seawater into the mixture. The hydrogen yield from the mixture decreased monotonically as the weight fraction of seawater was decreased. However, the measured yield was higher than the yield expected from the direct radiolysis of water in the mixture. Moreover the hydrogen yield was not so effectively decreased by the dilution of seawater in the mixture as in seawater alone. Therefore the additional formation of hydrogen should be considered in the evaluation of hydrogen production from radiolysis of the mixture of mordnite and water.
Nagaishi, Ryuji; Kumagai, Yuta; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
no journal, ,
no abstracts in English
Nagaishi, Ryuji; Kumagai, Yuta; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
no journal, ,
Radioactive water has been emitted following incidents at the Fukushima Dai-ichi Nuclear Power Station, and needed to be quickly decontaminated by the adsorption and/or the coagulation sedimentation of radioactive nuclides, where hydrogen molecules are produced by water radiolysis. The decontamination process with zeolites as absorbents of radioactive cesium was assumed, the observed yields of hydrogen production determined in mixtures of seawater and zeolite, and then the production rates estimated for the safety operation of process before the operation started.
Kumagai, Yuta; Nagaishi, Ryuji; Yamada, Reiji; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
no journal, ,
The amount of hydrogen produced in 
-radiolysis of mixture of seawater and mordenite was studied. The measured yield was decreased with decrease in the weight fraction of seawater. However, the yield was not simply proportional to the weight fraction of seawater and the influence of the mordenite was observed as additional production of hydrogen. At a weight fraction of seawater more than 0.2, the measured amount of hydrogen could be explained by an empirical equation given by a liner combination of two hydrogen production terms representing hydrogen production due to the energy deposition to seawater and that to mordenite. Each of the terms was expressed as a product of the absorbed energy and a yield given as the proportionality coefficient, and each of the yields could be a constant independent of the mixture ratio. The result imply an instinctive explanation of hydrogen production from the mixture of solid and liquid using the two respective yields.
Kumagai, Yuta; Nagaishi, Ryuji; Kimura, Atsushi; Taguchi, Mitsumasa; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru
no journal, ,
In the Fukushima Daiichi Nuclear Power Station, zeolite is used for decontamination of radioactive water as an adsorbent for radioactive Cs. During the process and the storage of the waste zeolite after the process, the management of hydrogen produced by water radiolysis is an important issue of safety. Thus hydrogen production from the mixture of zeolite and seawater was studied because the radioactive water contains salts from seawater. The hydrogen production from the mixture was decreased monotonically with decreasing weight fraction of seawater. However, the measured yield of hydrogen was higher than the yield expected from the direct radiolysis of water in the mixture. This result shows an additional production of hydrogen as an influence of zeolite. Moreover, dilution of seawater became less effective on the inhibition of hydrogen production with increasing weight fraction of zeolite, although it effectively decreased the hydrogen production in the absence of zeolite.
Yamagishi, Akihiko*; Yokobori, Shinichi*; Hashimoto, Hirofumi*; Yano, Hajime*; Imai, Eiichi*; Okudaira, Kyoko*; Kawai, Hideyuki*; Kobayashi, Kensei*; Tabata, Makoto*; Nakagawa, Kazumichi*; et al.
no journal, ,
no abstracts in English
Nagaishi, Ryuji; Inoue, Masao; Matsumura, Taichi; Yamagishi, Isao; Hino, Ryutaro; Ogawa, Toru
no journal, ,
Hydrogen gas generation in radiolysis of pure water or seawater coexisting with zeolite adsorbents has been investigated by using Co-60 -ray for hydrogen safety in decontamination of radioactive water after Fukushima Daiichi NPS accident. In this work, two types of void volumes present in the zeolite bed were paid attention microscopically, and the difference in water radiolysis between the volumes was considered. The oxygen generated by decomposition of hydrogen peroxide, as the counterpart of hydrogen molecule, contacting with the zeolites were also discussed.
