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Uchiyama, Yusuke*; Tokunaga, Natsuki*; Azuma, Kohei*; Kamidaira, Yuki; Tsumune, Daisuke*; Iwasaki, Toshiki*; Yamada, Masatoshi*; Tateda, Yutaka*; Ishimaru, Takashi*; Ito, Yukari*; et al.
Science of the Total Environment, 816, p.151573_1 - 151573_13, 2022/04
Times Cited Count:5 Percentile:71.31(Environmental Sciences)no abstracts in English
Sugawara, Takanori; Watanabe, Nao; Ono, Ayako; Nishihara, Kenji; Ichihara, Kyoko*; Hanzawa, Kohei*
Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 10 Pages, 2022/03
Japan Atomic Energy Agency (JAEA) has investigated an accelerator-driven system (ADS) to transmute minor actinides (MAs) included in high level wastes discharged from nuclear power plants. The ADS is a lead-bismuth cooled tank-type reactor with 800 MW thermal power. It is supposed that the ADS is safer than conventional critical reactors because it is operated in a subcritical state. The previous study performed the transient analyses for the typical ADS accidents such as unprotected loss of flow or beam overpower. It was shown that all calculation cases except loss of heat sink (LOHS) satisfied the no-damage criteria. To avoid the damage by LOHS, the ADS equips Direct Reactor Auxiliary Cooling System (DRACS) to remove the decay heat. The most important points of a DRACS operation are its reliability and to ensure the flowrate in a natural circulation state. This study aims to perform the CFD analysis of the natural circulation to clarify the flowrate in the ADS reactor vessel.
Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.
Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12
Times Cited Count:6 Percentile:52.8(Geosciences, Multidisciplinary)The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Otaka, Toshiki*; Sato, Tatsumi*; Ono, Shimpei; Nagoshi, Kohei; Abe, Ryoji*; Arai, Tsuyoshi*; Watanabe, So; Sano, Yuichi; Takeuchi, Masayuki; Nakatani, Kiyoharu*
Analytical Sciences, 35(10), p.1129 - 1133, 2019/10
Times Cited Count:7 Percentile:41.13(Chemistry, Analytical)Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count:233 Percentile:99.74(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Sano, Yuichi; Watanabe, So; Matsuura, Haruaki*; Nagoshi, Kohei*; Arai, Tsuyoshi*
Journal of Nuclear Science and Technology, 54(10), p.1058 - 1064, 2017/10
Times Cited Count:4 Percentile:37.32(Nuclear Science & Technology)For effective recovery of radioactive elements by adsorbents using polymer-immobilized silica (SiO-P) supports, the microstructure of SiO-P particles impregnated with CMPO as extractants and their change with the crosslinking degree of polymer (CDP) were investigated using STXM and EXAFS analyses; further, their relation with adsorption/elution behavior was discussed. The adsorption/elution tests using adsorbents with a different CDP demonstrated that a higher CDP inhibited the elution of adsorbed metal ions from the adsorbent. The results of STXM and EXAFS analyses suggested that adsorption by CMPO proceeds through the entire area in the adsorbent and the local structure around adsorbed metal ions is similar irrespective of the CDP. Conversely, STXM analyses implied the capture of eluents such as HO by polymers with high CDP, which suppresses the prompt elution of adsorbed metal ions from the adsorbent.
Tada, Kohei; Kitawaki, Shinichi; Watanabe, So; Aihara, Haruka; Shibata, Atsuhiro; Nomura, Kazunori
Proceedings of International Nuclear Fuel Cycle Conference (GLOBAL 2017) (USB Flash Drive), 3 Pages, 2017/09
Radioactive liquid waste containing chloride ion (Cl) is generated by chemical analysis for process control of pyroprocessing. To realize discharging this liquid waste to the sea, it's necessary to carry out the process in order to separate Cl and recover U, Pu. This study carried out a combination of the AgCl precipitation method and extraction chromatography method to separate Cl and recover U, Pu. The result of precipitation test showed that U and Pu didn't occur the co-precipitation after the test. The result of solid phase extraction test showed that 95% of Pu was successfully recovered from the liquid waste. It was difficult to analyze radioactivity about U because the concentration of U is not enough. These results showed that these process has the feasibility of the discharging the liquid waste to the sea.
Abe, Ryoji*; Nagoshi, Kohei*; Arai, Tsuyoshi*; Watanabe, So; Sano, Yuichi; Matsuura, Haruaki*; Takagi, Hideaki*; Shimizu, Nobutaka*; Koka, Masashi*; Sato, Takahiro*
Nuclear Instruments and Methods in Physics Research B, 404, p.173 - 178, 2017/08
Times Cited Count:5 Percentile:44.94(Instruments & Instrumentation)Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Otake, Makiko*; Arai, Takehiko*; Arai, Tomoko*; Hirata, Naru*; Hiroi, Takahiro*; Honda, Chikatoshi*; Imae, Naoya*; et al.
Space Science Reviews, 208(1-4), p.317 - 337, 2017/07
Times Cited Count:49 Percentile:72.49(Astronomy & Astrophysics)NIRS3: The Near Infrared Spectrometer is installed on the Hayabusa2 spacecraft to observe the target C-type asteroid 162173 Ryugu at near infrared wavelengths of 1.8 to 3.2 micrometer. It aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 micrometer-band. We adopted a linear-image sensor with indium arsenide (InAs) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 K, which enables to retaining sufficient sensitivity and noise level in the 3 micrometer wavelength region. We conducted ground performance tests for the NIRS3 flight model (FM) to confirm its baseline specifications. The results imply that the properties such as the signal-to-noise ratio (SNR) conform to scientific requirements to determine the degree of aqueous alteration, such as CM or CI chondrite, and the stage of thermal metamorphism on the asteroid surface.
Tanaka, Kazuya; Tanaka, Masato*; Watanabe, Naoko*; Tokunaga, Kohei*; Takahashi, Yoshio*
Chemical Geology, 460, p.130 - 137, 2017/06
Times Cited Count:7 Percentile:34.63(Geochemistry & Geophysics)Pd is highly accumulated in ferromanganese nodules and crusts relative to its concentration in seawater but the mechanism by which Pd(II) is incorporated remains poorly understood. We investigated the local coordination structure of Pd(II) adsorbed on -MnO, using X-ray absorption fine structure spectroscopy. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicated that Pd was adsorbed on -MnO through ligand exchange, from Cl coordination to O coordination. Furthermore, curve fitting of EXAFS spectra demonstrated the formation of two different inner-sphere complexes, bidentate-mononuclear and bidentate-binuclear complexes, and this finding was supported by density functional theory calculations. The formation of inner-sphere complexes is reasonable given the relatively large distribution coefficients obtained from adsorption experiments.
Nagoshi, Kohei*; Arai, Tsuyoshi*; Watanabe, So; Sano, Yuichi; Takeuchi, Masayuki; Sato, Mutsumi*; Oikawa, Hiroshi*
Nihon Ion Kokan Gakkai-Shi, 28(1), p.11 - 18, 2017/01
no abstracts in English
Yamasaki, Atsushi*; Fujiwara, Hidenori*; Tachibana, Shoichi*; Iwasaki, Daisuke*; Higashino, Yuji*; Yoshimi, Chiaki*; Nakagawa, Koya*; Nakatani, Yasuhiro*; Yamagami, Kohei*; Aratani, Hidekazu*; et al.
Physical Review B, 94(11), p.115103_1 - 115103_10, 2016/11
Times Cited Count:17 Percentile:61.47(Materials Science, Multidisciplinary)In this study, we systematically investigate three-dimensional(3D) momentum-resolved electronic structures of Ruddlesden-Popper-type iridium oxides SrIrO using soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO-plane structure. This transition occurs when the spin-orbit-coupled = 1/2 band changes its behavior in the dispersion relation and moves across the Fermi energy. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO and -dependent oscillations of photoelectron intensity in SrIrO. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole Brillouin zone and provides a panoramic view of electronic structures.
Adare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Armendariz, R.*; et al.
Physical Review C, 83(6), p.064903_1 - 064903_29, 2011/06
Times Cited Count:176 Percentile:99.41(Physics, Nuclear)Transverse momentum distributions and yields for , and in collisions at = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the RHIC. We present the inverse slope parameter, mean transverse momentum, and yield per unit rapidity at each energy, and compare them to other measurements at different collisions. We also present the scaling properties such as and scaling and discuss the mechanism of the particle production in collisions. The measured spectra are compared to next-to-leading order perturbative QCD calculations.
Adare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Aramaki, Y.*; et al.
Physical Review C, 83(4), p.044912_1 - 044912_16, 2011/04
Times Cited Count:7 Percentile:49.81(Physics, Nuclear)Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled collisions. Here we extend these studies to two particle correlations where one particle is an electron from the decay of a heavy flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interaction between heavy quarks and the quark-gluon matter. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to collisions.
Ara, Hiroshige*; Fukumitsu, Kenji*; Iizuka, Yunosuke*; Ishii, Takashi*; Izumiya, Yasushi*; Imazu, Masanori*; Utsugida, Yoshizo*; Hasegawa, Makoto*; Maeda, Masaya*; Yabe, Yukio*; et al.
PNC TJ199 84-04VOL1, 20 Pages, 1984/03
None
Kagei, Yusuke*; Kosono, Kohei*; Kutsuki, Katsuhiro*; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*
no journal, ,
Impact of high-density plasma nitridation of 4H-SiC(0001) surface on thermally grown SiO/SiC interface structure was investigated using synchrotron radiation X-ray photoemission spectroscopy. Surface nitridation was confirmed from Si2p and N1s spectra. Both Si sub-oxide and Si sub-nitride states at SiO/SiC interface was evaluated through deconvolution of Si2p spectra. We found that the amount of Si sub-oxide states increased with the oxidation time. However, the formation of Si sub-oxides was effectively suppressed by the surface nitridation treatment prior to oxidation. Since an interface state density of Al/SiO/SiC MOS capacitor was approximately halved by the surface nitridation treatment, a generation of interface defects was considered to be caused by the Si sub-oxides formation.
Watanabe, Heiji*; Kagei, Yusuke*; Kosono, Kohei*; Kirino, Takashi*; Watanabe, Yu*; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Yoshigoe, Akitaka; Teraoka, Yuden; et al.
no journal, ,
SiC-MOSFET's are expected for normally-off-type high performance power devices. Electrical defects due to residual inpurities such as carbon are in the interface of thermally-oxidized SiC-MOS's so that channel mobility is degraded preferentially. Although upgrade of reliability of a gate insulator is necessary for practical use, insulator degradation mechanisms have not well known yet. We are studying high quality MOS interface made by plasma nitridation techniques, upgrade of reliability and insulation by a stuck structure of a high-k insulator (AlON) layer and an SiO underlayer. Recent research results on those subjects are reported in this talk.
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.
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.