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spectrometry of terrestrial gamma rays using portable germanium detectors in area of 80 km radius around the Fukushima Daiichi Nuclear Power PlantMikami, Satoshi; Tanaka, Hiroyuki*; Okuda, Naotoshi*; Sakamoto, Ryuichi*; Ochi, Kotaro; Uno, Kiichiro*; Matsuda, Norihiro; Saito, Kimiaki
Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(4), p.159 - 178, 2021/12
In order to know the background radiation level where the area affected by the Fukushima Daiichi Nuclear Power Plant accident in 2011, terrestrial gamma rays had been measured by using portable germanium detectors repeatedly from 2013 through 2019, at 370 locations within 80 km radius area centered on the Fukushima Daiichi Nuclear Power Plant. Radioactive concentrations of Uranium 238, Thorium 232, Potassium 40 and kerma rates in air due to terrestrial gamma rays were obtained at those locations based on the method of ICRU report 53. Averaged concentrations of 
U, 
Th and 
K were 18.8, 22.7, 428 Bq/kg, respectively, and kerma rate in air over the area was found to be 0.0402 
Gy/h. The obtained kerma rates in air were compared to those reported in literatures. It was confirmed that the data were correlated with each other, and were agreed within the range of their uncertainty. This is because the kerma rate in air due to terrestrial gamma rays is depend on geology. The similar trend to previous findings was observed that the kerma rate in air at locations geologically classified as Mesozoic era, Granite and Rhyolite were statistically significantly higher than the others.
Mikami, Satoshi; Tanaka, Hiroyuki*; Matsuda, Hideo*; Sato, Shoji*; Hoshide, Yoshifumi*; Okuda, Naotoshi*; Suzuki, Takeo*; Sakamoto, Ryuichi*; Ando, Masaki; Saito, Kimiaki
Journal of Environmental Radioactivity, 210, p.105941_1 - 105941_12, 2019/12
Times Cited Count：24 Percentile：64.35(Environmental Sciences)The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of 
Cs with a half-life of 2.06y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of Cs and 
Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge.
Sano, Hiroyuki*; Fujisawa, Toshiharu*; Kimura, Akihiko*; Inoue, Masaki; Ukai, Shigeharu*; Onuki, Somei*; Okuda, Takanari*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9308_1 - 9308_5, 2009/05
Corrosion of structural materials is one of the serious problems when lead-bismuth eutectic alloy (LBE) is used as a coolant material in next generation nuclear systems. In this study, dissolution experiments of synthetic Fe-Cr-Al alloys and developed super ODS steel candidates into LBE under several partial pressures of oxygen were conducted. Dissolution behaviors of major components in such steels into LBE were investigated. Interfacial behavior between LBE and steels was also observed. In addition, partial potential diagrams of the Fe-Cr-Al-O system at several conditions were established as basic data. From the potential diagrams, the partial pressure range of oxygen was estimated for the stable protective oxide layer formation at the interface. At lower oxygen partial pressure than the pressure that is enough for the formation of the stable oxide layer, a rough oxide layer was formed at the interface in all samples, and the alloy elements dissolved into LBE through it. On the other hand, at the oxygen partial pressure to form stable oxide layer, a dense and very thin oxide layer was formed especially on the higher aluminum content steel, preventing the alloy dissolution into LBE. From the results, aluminum and chromium content in steel were very important for preventing the corrosion by LBE.
Yoshida, Mitsunori*; Tanaka, Nobuyuki; Okuda, Hiroyuki; Onuki, Kaoru
International Journal of Hydrogen Energy, 33(23), p.6913 - 6920, 2008/12
Times Cited Count：35 Percentile：62.91(Chemistry, Physical)The electro-electrodialysis (EED) for enhancing HI molality in HIx solution (HI-I
-HO mixture) of quasi-azeotropic composition was examined at 90 
C using Nafion 117 and graphite electrodes. The initial current efficiency of HI molality increase in catholyte varied in the range of 25-80% depending on the operation condition such that the higher iodine molality and the higher weight ratio of anolyte solution to catholyte solution resulted in the higher efficiency. With the progress of EED, the increase rate of the HI molality decreased and, in some cases, concentration limits were observed. Electric conductivity of the HIx solution, overvoltage of the electrode reaction, and voltage drop due to the membrane were measured in the temperature range of 25-120 C, which indicated that the EED cell voltage was governed by the voltage drop due to membrane.
Onuki, Kaoru; Kubo, Shinji; Terada, Atsuhiko; Iwatsuki, Jin; Takegami, Hiroaki; Okuda, Hiroyuki; Kasahara, Seiji; Tanaka, Nobuyuki; Imai, Yoshiyuki
Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10
Japan Atomic Energy Agency has been conducting R&D on thermochemical water-splitting Iodine-Sulfur (IS) process for hydrogen production. Closed-cycle operation of the process was demonstrated for one week with hydrogen production rate of about 30NL/h. Components in HSO
section were designed featuring a heat exchanger made of silicon carbide. Flowsheet process analysis is now in progress. For higher thermal efficiency, a Bunsen reactor and an EED cell are investigated. Vapor-liquid equilibrium of HI-HO-I for high pressure is measured.
O system and the HI+HO+I systemHodotsuka, Masatoshi; Yang, X.*; Okuda, Hiroyuki; Onuki, Kaoru
Journal of Chemical and Engineering Data, 53(8), p.1683 - 1687, 2008/07
Times Cited Count：29 Percentile：69.14(Thermodynamics)The isobaric Vapor Liquid Equilibrium(VLE) data in the pressure range of 0.11-0.58MPa where no experimental data had existed was measured for the purpose of increasing VLE data of hydriodic acid which is important physical properties which influence greatly the heat balance and mass balance in the thermochemical IS Cycle. Bubbling point and VLE data of hydriodic acid, which is prepared as adding iodine to almost azeotrope (57%) in the I/HI molar ratio from 0 to 4, were acquired at atmospheric pressure using a glass-made Othemer still. It was confirmed that the ratio of HI/HO of pseudo azeotrope increased as adding iodine. Furthermore, bubbling point and VLE data near the azeotrope in the high pressure range using a tantalum and Hastelloy made Gillespie still. The results quantitatively showed decrese of HI/HO molar ratio of azeotrope as increasing pressure, which used to be estimated by the result of measuring total pressure of hydriodic acid.
Kubo, Shinji; Nakajima, Hayato; Imai, Yoshiyuki; Kasahara, Seiji; Tanaka, Nobuyuki; Okuda, Hiroyuki; Miyashita, Reiko*; Onuki, Kaoru
Proceedings of 17th World Hydrogen Energy Conference (WHEC 2008) (CD-ROM), 4 Pages, 2008/06
A new technique was developed to estimate compositions of Bunsen reaction solution in liquid-liquid phase separation which was targeted on the two solutions in phase equilibrium. In this technique, just two densities measured in the two solution are employed to estimate compositions of two solutions consisting of HI, HSO, I, HO. The fundamental equations underlying this estimation is relations between densities and compositions. To formulate the relations, densities of simulated Bunsen reaction solutions were measured and regression expressions were formulated. Moreover, relational equations for both phases were set up from measured values by the regression procedure. Through estimations of both compositions from both densities, the calculated values are approximately consistent with titrated values. Because of easily and simply execution, this technique is useful for practical use, especially for plant operation and equipment design.
Sakaba, Nariaki; Tachibana, Yukio; Shimakawa, Satoshi; Ohashi, Hirofumi; Sato, Hiroyuki; Yan, X.; Murakami, Tomoyuki; Ohashi, Kazutaka; Nakagawa, Shigeaki; Goto, Minoru; et al.
JAEA-Technology 2008-019, 57 Pages, 2008/03
JAEA-Technology-2008-019.pdf:8.59MB
The small-sized and safe cogeneration High Temperature Gas-cooled Reactor (HTGR) that can be used not only for electric power generation but also for hydrogen production and district heating is considered one of the most promising nuclear reactors for developing countries where sufficient infrastructure such as power grids is not provided. Thus, the small-sized cogeneration HTGR, named High Temperature Reactor 50-Cogeneration (HTR50C), was studied assuming that it should be constructed in developing countries. Specification, equipment configuration, etc. of the HTR50C were determined, and economical evaluation was made. As a result, it was shown that the HTR50C is economically competitive with small-sized light water reactors.
Kubo, Shinji; Imai, Yoshiyuki; Ohashi, Hirofumi; Kasahara, Seiji; Tanaka, Nobuyuki; Okuda, Hiroyuki; Onuki, Kaoru
Proceedings of 2007 AIChE Annual Meeting (CD-ROM), 5 Pages, 2007/11
no abstracts in English
Tanaka, Nobuyuki; Yoshida, Mitsunori; Okuda, Hiroyuki; Sato, Hiroyuki; Kubo, Shinji; Onuki, Kaoru
Proceedings of International Conference on Advanced Nuclear Fuel Cycles and Systems (Global 2007) (CD-ROM), p.833 - 836, 2007/09
Breakdown of the cell voltage in the electro-electrodialysis process for concentrating HIx solution (HI-HO-I mixture) was preliminarily examined in an effort to clarify the optimal operation condition as well as to optimize the cell design for the application to the thermochemical water-splitting IS process for large-scale hydrogen production. Basic data such as electric resistance of HIx solution, overvoltage of the iodine-iodide ion redox reaction at graphite electrode, and the membrane voltage drop, were measured using HIx solution with composition of interest. Also, a methodology for estimating the cell voltage was discussed. The calculated cell voltage agreed well with the experimental one indicating the validity of the procedure adopted.
Terada, Atsuhiko; Iwatsuki, Jin; Ishikura, Shuichi; Noguchi, Hiroki; Kubo, Shinji; Okuda, Hiroyuki; Kasahara, Seiji; Tanaka, Nobuyuki; Ota, Hiroyuki*; Onuki, Kaoru; et al.
Journal of Nuclear Science and Technology, 44(3), p.477 - 482, 2007/03
Times Cited Count：46 Percentile：92.93(Nuclear Science & Technology)Japan Atomic Energy Agency (JAEA) has been conducting study on thermochemical IS process for hydrogen production. A pilot test of IS process is under planning that covers four R&D subjects: (1) construction of a pilot test plant made of industrial materials and completion of hydrogen production test using electrically-heated helium gas as the process heat supplier, (2) development of analytical code system, (3) component tests to assist the hydrogen production test and also to improve the process performance for the commercial plant, (4) design of HTTR-IS system. Development of innovative chemical reactors is in progress, which are equipped with ceramic heat exchanger. In design of the IS plant, it is important to establish the system for "design by analysis". Therefore, we have developed a multi-phase flow analysis code that can analyze systems in which chemical reactions occur
Okuda, Hiroyuki; Yamaki, Tetsuya; Kubo, Shinji
Proceedings of AIChE 2006 Spring National Meeting (CD-ROM), 6 Pages, 2006/00
no abstracts in English
Nomura, Mikihiro*; Okuda, Hiroyuki; Kasahara, Seiji; Nakao, Shinichi*
Chemical Engineering Science, 60(24), p.7160 - 7167, 2005/12
Times Cited Count：29 Percentile：65.11(Engineering, Chemical)The Bunsen reaction (SO+I+2HO=HSO+2HI) in the water-splitting IS process was examined using an electrochemical cell with a cation exchange membrane. The optimal molalities of anolyte and catholyte were evaluated by total thermal efficiency. The I/HI ratio had little effect on the required total voltage; the I/HI ratio can be reduced to 0.5 without decreasing the efficiency. HI and HSO molality greatly affected the efficiency. Membrane resistances are very important parameters affecting the efficiency. The total thermal efficiency increased by 3.0% by increasing the operating temperature from 313K to 363K.
Kubo, Shinji; Kasahara, Seiji; Okuda, Hiroyuki; Terada, Atsuhiko; Tanaka, Nobuyuki; Inaba, Yoshitomo; Ohashi, Hirofumi; Inagaki, Yoshiyuki; Onuki, Kaoru; Hino, Ryutaro
Nuclear Engineering and Design, 233(1-3), p.355 - 362, 2004/10
Times Cited Count：62 Percentile：95.48(Nuclear Science & Technology)no abstracts in English
Hodotsuka, Masatoshi; Yang, X.*; Okuda, Hiroyuki
no journal, ,
The VLE data of Hydriodic acid have been measured.
Yoshida, Mitsunori; Tanaka, Nobuyuki; Okuda, Hiroyuki; Kubo, Shinji; Onuki, Kaoru; Hino, Ryutaro
no journal, ,
no abstracts in English
Hodotsuka, Masatoshi; Yang, X.*; Okuda, Hiroyuki; Kubo, Shinji; Onuki, Kaoru; Hino, Ryutaro
no journal, ,
no abstracts in English
Hodotsuka, Masatoshi; Okuda, Hiroyuki; Yoshida, Mitsunori; Kubo, Shinji; Onuki, Kaoru; Hino, Ryutaro
no journal, ,
no abstracts in English
Ijichi, Masanori; Yoshida, Mitsunori; Isaka, Kazuyoshi; Tanaka, Nobuyuki; Kasahara, Seiji; Okuda, Hiroyuki; Hodotsuka, Masatoshi; Kanagawa, Akihiro; Imai, Yoshiyuki; Noguchi, Hiroki; et al.
no journal, ,
no abstracts in English
Yoshida, Mitsunori; Okuda, Hiroyuki; Hodotsuka, Masatoshi; Kubo, Shinji; Onuki, Kaoru; Hino, Ryutaro
no journal, ,
no abstracts in English
