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Ogura, Koya*; Hosoda, Masahiro*; Tamakuma, Yuki*; Suzuki, Takahito*; Yamada, Ryohei; Negemi, Ryoju*; Tsujiguchi, Takakiyo*; Yamaguchi, Masaru*; Shiroma, Yoshitaka*; Iwaoka, Kazuki*; et al.
International Journal of Environmental Research and Public Health, 18(3), p.978_1 - 978_16, 2021/02
Times Cited Count：7 Percentile：68.83(Environmental Sciences)Nagae, Daisuke*; Abe, Yasushi*; Okada, Shunsuke*; Omika, Shuichiro*; Wakayama, Kiyoshi*; Hosoi, Shun*; Suzuki, Shinji*; Moriguchi, Tetsuro*; Amano, Masamichi*; Kamioka, Daiki*; et al.
Nuclear Instruments and Methods in Physics Research A, 986, p.164713_1 - 164713_7, 2021/01
Times Cited Count：5 Percentile：65.59(Instruments & Instrumentation)Heged
s, M.*; Shiroma, Yoshitaka*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Suzuki, Takahito*; Tamakuma, Yuki*; Yamada, Ryohei; Tsujiguchi, Takakiyo*; Yamaguchi, Masaru*; Ogura, Koya*; et al.
Journal of Radioanalytical and Nuclear Chemistry, 323(1), p.197 - 204, 2020/01
Times Cited Count：3 Percentile：31.89(Chemistry, Analytical)The radioactivity of cesium in the water and sediments of two major rivers was measured along with airborne radioactivity in Namie Town, after the recent partial lift on the evacuation order in 2017. The observed concentrations were up to 384 
11 mBq/L for 
Cs in unfiltered water and 1.28 0.09 mBq/m
for Cs in air, while the sediment had a maximum of 44900 23.4 Bq/kg for Cs. The 
Cs/Cs ratios indicate the main origin of the cesium in the sediment to be Unit 1 in good agreement with previous reports on the accident.
Kotake, Shoji*; Chikazawa, Yoshitaka; Takaya, Shigeru; Otaka, Masahiko; Kubo, Shigenobu; Arai, Masanobu; Kunogi, Kosuke; Ito, Takaya*; Yamaguchi, Akira*
Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04
A maintenance management required to prototype nuclear power reactors is proposed. Monitoring and control of sodium impurity and thermal transient are extremely important for sodium boundary maintenance for sodium-cooled fast reactors. At the fast stage of the prototype reactor Monju operation, degradation mechanism on the piping should be demonstrated based on operation experiences. Therefore inspection on a representative position for crack indication and pipe thickness is proposed. Due to less experience of SFR plants, early detection of boundary failure is considered. For a matured operation stage, when degradation mechanism is well demonstrated based on inspection data, inspection cycle could be extended. And for commercial reactors, maintenance without inspection will be established based on accumulated operation experiences including those of the prototype reactor Monju.
Arai, Masanobu; Kunogi, Kosuke; Aizawa, Kosuke; Chikazawa, Yoshitaka; Takaya, Shigeru; Kubo, Shigenobu; Kotake, Shoji*; Ito, Takaya*; Yamaguchi, Akira*
Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04
Applications for maintenance program on piping support of prototype fast breeder reactor Monju are studied. Based on degradation mechanism, snubbers in Monju primary cooling system showed lifetime more than the plant lifetime of 30 years by experiments conservatively. For the first step during construction, visual inspection on accessible all supports could be available. In that visual inspection, mounting conditions and damages of all accessible supports could be monitored. One of major features of the Monju primary piping system is large thermal expansion due to large temperature difference between maintenance and operation conditions. Thanks to that large thermal expansion, integrity of the piping support could be monitored by measuring piping displacement. When technologies of piping displacement monitoring are matured in Monju, visual inspection on piping support could be shifted to piping displacement monitoring. At that stage, the visual inspection could be limited only on representative supports.
Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Yamaguchi, Yoshihito; Onizawa, Kunio; et al.
Journal of Nuclear Materials, 452(1-3), p.235 - 240, 2014/09
Times Cited Count：40 Percentile：95.16(Materials Science, Multidisciplinary)Microstructures and hardness of stainless steel weld overlay cladding of reactor pressure vessels subjected to the thermal aging at 400 
C for 100-10,000 h were investigated using atom probe tomography and nanoindentation technique. The Cr concentration fluctuation in the 
-ferrite phase caused by spinodal decomposition rapidly progressed by the 100 h aging while NiSiMn clusters increased in number density at 2,000 h and coarsened at 10,000 h. The hardness of the -ferrite phase also rapidly increased at the short aging time. The Cr concentration fluctuation and the hardness were in good correlation with the degree of the Cr concentration fluctuation rather than the formation of the NiSiMn clusters. These results strongly suggested that the dominant factor of the hardening of the -ferrite phase by the thermal aging was Cr spinodal decomposition.
Cs discharge rates after the Fukushima Dai-ichi Nuclear Power Plant accident from two distinct watershed simulation modelsKitamura, Akihiro; Imaizumi, Yoshitaka*; Yamaguchi, Masaaki; Yui, Mikazu; Suzuki, Noriyuki*; Hayashi, Seiji*
Kankyo Hoshano Josen Gakkai-Shi, 2(3), p.185 - 192, 2014/09
Annual discharge rates of radioactive cesium through selected rivers due to the Fukushima Dai-ichi Nuclear Power Plant accident were simulated by two different watershed models. One is the Soil and Cesium Transport, SACT, model which was developed by Japan Atomic Energy Agency and the other one is the Grid-Catchment Integrated Modeling System, G-CIEMS, which was developed by National Institute of Environmental Studies. We choose the Abukuma, the Ukedo, and the Niida rivers for the present study. Comparative results showed that while components and assumptions adopted in two models differ, both methods predicted the same order of magnitude estimates.
Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Yamaguchi, Yoshihito; Onizawa, Kunio
Journal of Nuclear Materials, 449(1-3), p.273 - 276, 2014/06
Times Cited Count：19 Percentile：81.57(Materials Science, Multidisciplinary)Microstructural changes and hardness of stainless steel weld overlay cladding of reactor pressure vessels subjected to the neutron irradiation with a dose of 7.2 
10
n cm
(E 
1 MeV) and a flux of 1.1 10
n cm s
at 290C were investigated by atom probe tomography and with nanoindentation technique. In order to isolate the effect of the irradiation, we compared the results of the measurements of the irradiated sample with that of the aged one at 300C for the time equivalent to the irradiation. The Cr concentration fluctuation was enhanced in the -ferrite phase of the irradiated sample. In addition, the enhancement of the concentration fluctuation of Si, which was not observed in the aged sample, was observed. The hardening at the -ferrite phase was occurred by both the irradiation and the aging. However, the former was more than that expected from the Cr concentration fluctuation, which suggested that the Si concentration fluctuation and irradiation-induced defects were possible origins of the additional hardening.
113 of the 113th elementMorita, Kosuke*; Morimoto, Koji*; Kaji, Daiya*; Haba, Hiromitsu*; Ozeki, Kazutaka*; Kudo, Yuki*; Sumita, Takayuki*; Wakabayashi, Yasuo*; Yoneda, Akira*; Tanaka, Kengo*; et al.
Journal of the Physical Society of Japan, 81(10), p.103201_1 - 103201_4, 2012/10
Times Cited Count：167 Percentile：97.27(Physics, Multidisciplinary)An isotope of the 113th element, 113, was produced in a nuclear reaction with a 
Zn beam on a 
Bi target. We observed six consecutive 
decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector, in extremely low background condition. The fifth and sixth decays are fully consistent with the sequential decays of 
Db and 
Lr both in decay energies and decay times. This indicates that the present decay chain consisted of 113, 
Rg (Z = 111), 
Mt (Z = 109), 
Bh (Z = 107), Db (Z = 105), and Lr (Z = 103) with firm connections. This result, together with previously reported results from 2004 and 2007, conclusively leads the unambiguous production and identification of the isotope 113, of the 113th element.
Hamada, Kazuya; Kawano, Katsumi; Ebisawa, Noboru; Nakajima, Hideo; Yano, Yoshitaka*; Yamaguchi, Takanori*
Proceedings of 24th International Cryogenic Engineering Conference (ICEC 24) and International Cryogenic Materials Conference 2012 (ICMC 2012) (CD-ROM), p.559 - 562, 2012/05
The Japan Atomic Energy Agency (JAEA) has the responsibility to procure 25% of the ITER Toroidal Field Coil conductors and 100% of Central Solenoid Conductor as the Japanese Domestic Agency (JADA) in the ITER project. The TF conductor is composed of 900 Nb
Sn superconducting strands and 522 Cu strands protected by a circular sheath tube (jacket) with an outer diameter of 43.7 mm. The TF conductor has a central spiral cooling tube and a coolant flows into the cable space and the central channel in parallel. JAEA has measured a pressure drop characteristic of more than 20 TF conductors having different length using nitrogen gas at room temperature as a part of acceptance test. The measurement results are normalized to friction factor as a function of Reynolds number to check the difference of each other. The results show the normalized pressure drop characteristic is same among conductors. This is one of evidences that TF conductor is manufactured uniformly.
Kamei, Gento; Honda, Akira; Mihara, Morihiro; Oda, Chie; Ichige, Satoru; Kurimoto, Yoshitaka; Hoshino, Seiichi; Akagi, Yosuke; Sato, Nobuyuki; Murakami, Hiroshi*; et al.
JAEA-Research 2011-002, 82 Pages, 2011/03
JAEA-Research-2011-002.pdf:5.64MB
Based on Japanese governmental policy and general scheme, research and development of geological disposal technology for TRU waste has been proceeding to improve reliability of the safety assessment of the co-locational disposal of TRU waste and of HLW, to expand the basement of generic safety assessment, and to develop the alternative technology to cope with the broad geologic environment of Japan. Japan Atomic Energy Agency is dealing with the assignments in the governmental generic scheme. We report here the progress of the studies at the end of H20 (2008) Japanese fiscal year, which are (1) evaluation of long-term mechanical stability in the near-field including development of a creep mode of rock and analyses of mechanical behavior of TRU waste repository, (2) performance assessment of the disposal system including data acquisition and preparation on radionuclides migration, cementitious material alteration, bentonite and hostrock alteration with alkaline solution and nitrate effect, and (3) alternative technology development including decomposition of nitrate.
Bh and Db produced in the 
Cm + 
Na reactionMorita, Kosuke*; Morimoto, Koji*; Kaji, Daiya*; Haba, Hiromitsu*; Ozeki, Kazutaka*; Kudo, Yuki*; Sato, Nozomi*; Sumita, Takayuki*; Yoneda, Akira*; Ichikawa, Takatoshi*; et al.
Journal of the Physical Society of Japan, 78(6), p.064201_1 - 064201_6, 2009/06
Times Cited Count：30 Percentile：78.34(Physics, Multidisciplinary)Decay properties of an isotope Bh and its daughter nucleus Db produced by the Cm(Na,5
) reaction were studied by using a gas-filled recoil separator coupled with a position-sensitive semiconductor detector. Bh was clearly identified from the correlation of the known nuclide, Db. The obtained decay properties of Bh and Db are consistent with those observed in the 113 chain, which provided further confirmation of the discovery of 113.
Matsushita, Yoshitaka*; Izumi, Fujio*; Kobayashi, Kiyoshi*; Igawa, Naoki; Kitazawa, Hideaki*; Oyama, Yukiko*; Miyoshi, Shogo*; Yamaguchi, Shu*
Nuclear Instruments and Methods in Physics Research A, 600(1), p.319 - 321, 2009/02
Times Cited Count：22 Percentile：80.43(Instruments & Instrumentation)The neutron powder diffraction data of the apatite-type La-silicate La
Si
O
was measured at 10 K and the Rietveld refinement on the basis of hexagonal P6/m was successfully carried out. The obtained cell parameters were 
=0.971297(7) nm, and 
= 0.717950(6) nm. On the Rietveld refinement supported by maximum entropy method, the interstitial oxygen positions show randomly distribution around La2 site, and they may give the driving-force of high ionic conductivity to the main ionic conduction site O4.
Kobayashi, Kiyoshi*; Matsushita, Yoshitaka*; Igawa, Naoki; Izumi, Fujio*; Nishimura, Chikashi*; Miyoshi, Shogo*; Oyama, Yukiko*; Yamaguchi, Shu*
Solid State Ionics, 179(38), p.2209 - 2215, 2008/11
Times Cited Count：24 Percentile：67.78(Chemistry, Physical)A novel synthesis method of lanthanum silicate apatite was developed by a sol-gel method using an aqueous solution system. The processes of apatite phase formation were investigated by XRD and TG-DTA. Lanthanum dioxide carbonate was found in the sample below 873 K and lanthanum silicate apatite was formed above 1073 K. It was founded that the profiles of powder XRD and neutron diffraction could be refined by the oxy-apatite structure with the space group 
6/
.
Fujii, Tadashi; Chikazawa, Yoshitaka; Konomura, Mamoru; Yamaguchi, Akira
Saikuru Kiko Giho, (26), 0 Pages, 2005/00
The conceptual design study of sodium cooled reactor is in progress in the Feasibility Study on Commercialized Fast Reactor Cycle Systems. The cooling system is composed of two loops in order to reduce plant construction cost. With loop number reduction, large diameter pipings are adopted and mean velocity in the piping also increases in comparison with former design. As for these piping systems, knowledge concerning hydraulic behaviors around the elbow and vibration phenomenon which is caused by the turbulence of fluid was insufficient. Therefore, flow-induced vibration tests have been started using water test facility, which simulates a hot leg piping of primary cooling system of large-scale reactor at the 1/3 reduced scale. Until now, flow visualization was conducted using acryl model and hydraulic behaviors such as velocity distributions in the piping were clarified. Further, as for the pressure fluctuations of the fluid which become vibration sources to the piping, it confirmed that the pressure fluctuations in the piping could be divided into four sections according to the degree of the turbulence caused at flow separation in the elbow.
Konomura, Mamoru; Ogawa, Takashi; Okano, Yasushi; Yamaguchi, Hiroyuki; Murakami, Tsutomu; Takaki, Naoyuki; Nishiguchi, Youhei; Sugino, Kazuteru; Naganuma, Masayuki; Hishida, Masahiko; et al.
JNC TN9400 2004-035, 2071 Pages, 2004/06
JNC-TN9400-2004-035.pdf:76.42MB
The attractive concepts for Sodium-, lead-bismuth-, helium- and water-cooled FBRs have been created through using typical plant features and employing advanced technologies. Efforts on evaluating technological prospects of feasibility have been paid for these concepts. Also, it was comfirmed if these concepts satisfy design requierments of capability and performance presumed in the feasibilty study on commertialization of Fast Breeder Reactor Systems. As results, it was concluded that the selection of sodium-cooled reactor was most rational for practical use of FBR technologies in 2015.
Imanaka, Masayo*; Nagao, Seiya; Nakaguchi, Yuzuru*; Yamaguchi, Yoshitaka*; Suzuki, Yasuhiro*; Murakami, Masahiro*; Hiraki, Keizo*
Proceedings of International Conference on the Biogeochemistry of Trace Elements (ICOBTE2001), P. 662, 2001/00
no abstracts in English
Takata, Takashi*; Kohara, Yoshitaka*; Yamaguchi, Akira*; Ohshima, Hiroyuki
no journal, ,
no abstracts in English
Kohara, Yoshitaka*; Yamaguchi, Akira*; Takata, Takashi*; Ohshima, Hiroyuki
no journal, ,
We have a plan to perform a fundamental experiment to investigate the mechanism of sodium-water chemical reaction. For help in setting the experimental conditions, a numerical simulation was performed for clarifying the effect of ambient gas pressure and water vapor concentration on the position and the region of the counterflow diffusion flame of sodium and water vapor. The result shows that the area of the diffusion flame is enlarged as the gas pressure is reduced and therefore low pressure condition is recommended to keep high accuracy of measurement.
Kobayashi, Kiyoshi*; Yoshida, Akira*; Matsushita, Yoshitaka*; Nishimura, Chikashi*; Oyama, Yukiko*; Miyoshi, Shogo*; Izumi, Fujio*; Igawa, Naoki; Yamaguchi, Shu*
no journal, ,
Conduction properties of oxide ions and crystal structure refinement of La
(SiO
)O
have been made by A.C.-impedance, electro-motive force of oxygen concentration cell, X-ray and neutron diffraction methods using the sample fabricated by the sol-gel method. The crystal structure of the sample can be refined by structural model with 6/ space group. Oxide ion conductivity is found to be predominant in wide oxygen partial pressure and temperature range based on the conductivity and electro-motive force measurements.
