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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：43 Percentile：96.93(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.
Kubota, Masato; Nigo, Seisuke*; Kato, Seiichi*; Amemiya, Kenta*
AIP Advances (Internet), 9(9), p.095050_1 - 095050_4, 2019/09
Times Cited Count：1 Percentile：4.41(Nanoscience & Nanotechnology)We measured the X-ray absorption spectra of amorphous alumina with vacancy-type oxygen defects which exhibits the resistance random access memory effect. For the first time, we detected changes in the electronic structure owing to the memory effect. A major difference in spectrum was observed near the O K-absorption edge.
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：259 Percentile：99.73(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.
Horie, Hiroki*; Yukumatsu, Kazuki*; Mishima, Fumihito*; Akiyama, Yoko*; Nishijima, Shigehiro*; Sekiyama, Tomio*; Mitsui, Seiichiro; Kato, Mitsugu
Journal of Physics; Conference Series, 871, p.012102_1 - 012102_7, 2017/07
Times Cited Count：1 Percentile：49.63(Physics, Applied)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：54 Percentile：71.62(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.
Saito, Hiroyuki; Kato, Seiichi*; Katagiri, Masahiko*
Materials Transactions, 55(8), p.1114 - 1116, 2014/08
Times Cited Count：2 Percentile：12.26(Materials Science, Multidisciplinary)Ikusawa, Yoshihisa; Ozawa, Takayuki; Hirooka, Shun; Maeda, Koji; Kato, Masato; Maeda, Seiichiro
Proceedings of 22nd International Conference on Nuclear Engineering (ICONE-22) (DVD-ROM), 6 Pages, 2014/07
In order to develop MA contained MOX (MA-MOX) fuel design method, the analysis models to predict irradiation behavior of MA-MOX fuel have to be developed and the accuracy of irradiation behavior analysis code should be evaluated with the result of post-irradiation examinations (PIEs) for MA-MOX fuels. In this study, we developed the computer module "TRANSIT" to compute thermal properties of MA-MOX fuel. TRANSIT can give thermal conductivity, melting temperature and vapor pressures of MA-MOX. By using this module, we improved the thermal behavior analysis code "DIRAD" and developed DIRAD-TRANSIT code system to compute the irradiation behavior of MA-MOX fuel. This system was verified with the results of PIEs for the conventional MOX fuels and the MA-MOX fuels irradiated in the experimental fast reactor "JOYO". As the result of the verification, it can be mentioned that the DIRAD-TRANSIT system would precisely predict the fuel thermal behavior, i.e. fuel temperature and fuel restructuring, for oxide fuels containing several percent minor actinides.
Yamamoto, Seiichi*; Watabe, Hiroshi*; Kawachi, Naoki; Fujimaki, Shu; Kato, Katsuhiko*; Hatazawa, Jun*
Nuclear Instruments and Methods in Physics Research A, 743, p.124 - 129, 2014/04
Times Cited Count：10 Percentile：57.19(Instruments & Instrumentation)Nigo, Seisuke*; Kubota, Masato; Harada, Yoshitomo*; Hirayama, Taisei*; Kato, Seiichi*; Kitazawa, Hideaki*; Kido, Giyu*
Journal of Applied Physics, 112(3), p.033711_1 - 033711_6, 2012/08
Times Cited Count：61 Percentile：89.42(Physics, Applied)Imaizumi, Tomomi; Miyauchi, Masaru; Ito, Masayasu; Watahiki, Shunsuke; Nagata, Hiroshi; Hanakawa, Hiroki; Naka, Michihiro; Kawamata, Kazuo; Yamaura, Takayuki; Ide, Hiroshi; et al.
JAEA-Technology 2011-031, 123 Pages, 2012/01
JAEA-Technology-2011-031.pdf:16.08MB
The number of research reactors in the world is decreasing because of their aging. However, the planning to introduce the nuclear power plants is increasing in Asian countries. In these Asian countries, the key issue is the human resource development for operation and management of nuclear power plants after constructed them, and also the necessity of research reactor, which is used for lifetime extension of LWRs, progress of the science and technology, expansion of industry use, human resources training and so on, is increasing. From above backgrounds, the Neutron Irradiation and Testing Reactor Center began to discuss basic concept of a multipurpose low-power research reactor for education and training, etc. This design study is expected to contribute not only to design tool improvement and human resources development in the Neutron Irradiation and Testing Reactor Center but also to maintain and upgrade the technology on research reactors in nuclear power-related companies. This report treats the activities of the working group from July 2010 to June 2011 on the multipurpose low-power research reactor in the Neutron Irradiation and Testing Reactor Center and nuclear power-related companies.
Tatsumoto, Hideki; Aso, Tomokazu; Otsu, Kiichi; Uehara, Toshiaki; Sakurayama, Hisashi; Kawakami, Yoshihiko; Kato, Takashi; Futakawa, Masatoshi; Yoshinaga, Seiichiro*
Proceedings of International Cryogenic Engineering Conference 23 (ICEC-23) and International Cryogenic Materials Conference 2010 (ICMC 2010), p.377 - 382, 2010/07
A dynamic gas bearing centrifugal pump that circulated supercritical hydrogen with a large flow rate of more than 0.16 kg/s was developed to minimize the hydrogen density change at the moderator. The two pumps were simultaneously operated in parallel for redundancy. The performance test results indicated that the dimensionless characteristics for the single and the parallel operations existed on an identical curve. An outstanding peak adiabatic efficiency exited at the flow coefficient of 0.046, independently of the revolution. It was verified that the developed hydrogen pump satisfied the design requirement.
Yang, J.*; Kondo, Takafumi*; Norizawa, Kimihiro*; Nagaishi, Ryuji; Taguchi, Mitsumasa; Takahashi, Kenji*; Kato, Ryuji*; Anishchik, S. V.*; Yoshida, Yoichi*; Tagawa, Seiichi*
Radiation Physics and Chemistry, 77(10-12), p.1233 - 1238, 2008/10
Times Cited Count：25 Percentile：82.53(Chemistry, Physical)First observation of picosecond dynamics in ionic liquid of DEMMA-TFSI in radiation chemistry was reported. It is found that the electron produced by ionization is solvated to full solvation in ionic liquid with a rate constant of 3.9
10
s
. The yield of solvated electrons in picosecond time region is 1.210
mol J. The dry electron in ionic liquid reacts rapidly with biphenyl and pyrene with a rate constant of 3.8 to 7.910
L mol s. The geminate ion recombination in n-dodecane and n-hexane was also observed by monitoring the transient absorptions at 523 nm.
Kato, Yuko; Umebayashi, Eiji; Okimoto, Yutaka; Okuda, Eiichi; Takayama, Koichi; Ozawa, Takayuki; Maeda, Seiichiro; Matsuzaki, Masaaki; Yoshida, Eiichi; Maeda, Koji; et al.
JAEA-Research 2007-019, 56 Pages, 2007/03
JAEA-Research-2007-019.pdf:6.79MB
In order to resume the System Startup Test (SST) of Monju, replacement fuel have to be loaded in exchange for some of initial fuel now loaded in the core to compensate core reactivity lost by decay of Pu-241 in them. The replacement fuel were being stored either in sodium in an ex-vessel storage tank or in air in a storage rack for about 10 years since their fabrication. The initial fuel were irradiated during the SST which was suspended in the end of 1995 and then stayed being loaded in the sodium-circulated core. As this long-term storage and loading may deteriorate mechanical integrity of the assemblies, a study has been made thoroughly on its thermal-hydraulic, structural and material effects on them that might be caused by irradiation in the core, sodium and mechanical environment. The study has shown that the mechanical integrity of them is well maintained even with this long-term storage and loading.
Ioka, Seiichiro; Iwatsuki, Teruki; Kato, Osamu*; Imakita, Tsuyoshi*
Bunseki Kagaku, 55(10), p.793 - 797, 2006/10
Times Cited Count：1 Percentile：4.65(Chemistry, Analytical)Performance test for redox potential measurement of solution was conducted using continuous polished and untreated Platinum working electrodes in under inert condition. The redox potential measured by polished electrode immediately shows steady value, and approximately coincides with the equilibrium value of redox reaction between HS
and S
. Then the redox potentials would be controlled by the equilibrium of the redox reaction. On the other hand, redox potential measured by untreated electrode was +0.2V higher than that measured by continuous polished electrode. The redox potential measured implies that the SO is dominant species in solution. Disagreement of redox potentials measured by polished and untreated electrodes may be caused by deactivation of platinum electrode of adsorption of sulfuric acid anions.
Odaka, Susumu; Kato, Shoichi; Yoshida, Eiichi; Kawakami, Tomohiro*; Suzuki, Takaichi*; Kawashima, Seiichi*; Ishigami, Katsuo*
JNC TN9450 2005-001, 196 Pages, 2005/03
Material test of 316FR steel, which was used for structure material of fast breeder reactor (FBR) has been preformed in New Technology Development Group. In this report, the result of test obtained up to this time was collected. Many valuable data that long time test more than 40000 hours including sodium environment test data in this report will be use for material examination of FBR in the future.Contents of the data sheet are as follows; (1) Material: 316FR Steel, (2) Test environment: In air,in sodium, (3) Test emperature: Room temperature to 800, (4) Test method: According to JIS and FBR metallic materials test manual (Revised edition), (5) Number of data:Tensile tests 234, Creep tests 408, Fatigue tests 201, Creep-fatigue tests 47, Relaxation tests 6,Total 896 This report consists of the printouts fromthe structural material data processing system, SMAT.
Takeda, Seiichiro; ; ; ; Kato, Toshihiro*; *; Fujisaku, Kazuhiko*
JNC TN8400 2002-007, 135 Pages, 2001/12
JNC-TN8400-2002-007.pdf:9.39MB
Corrosion performance of materials used for nuclear fuel reprocessing plant was studied for the extension of their lifetime during in-service period. Research was performed focusing on characteristics of reprocessing solution which is very important corrosion factor on environmental side. In the first stage, fundamental corrosion behavior of several kinds of candidate materials such as 304ULC, 310Nb, Ti, Ti-5Ta and Zr was investigated in pure nitric acid solution. Then corrosion performance of such materials in reprocessing environment was made cleared by means of so-called hot test which is used actual reprocessing solution under radioactive conditions. The results are summarized as follows. (1) With regards to the effects of uranium and plutonium on corrosion, high valence plutonium (Pu(Ⅵ)) accelerated the corrosion of stainless steels in nitric acid, but uranium did not affect on them. It is caused by trans-passive dissolution based on the shift of corrosion potential to the noble position. It is thought that the potential shift is caused by increase of the cathodic current on the stainless steel surface due to the reduction of Pu(Ⅵ) to Pu(IV). (2) In fission product (FP) elements, ruthenium accelerated the corrosion of stainless steel in nitric acid when its concentration was comparatively high. Other FP's did not affect on them. The corrosion potential of stainless steel shifts toward noble region by adding ruthenium in nitric acid where high corrosion rates are exhibited. It is thought that the potential shift is caused by the enhancement of cathodic reactions on metal surface due to co-existence of ruthenium in nitric acid. (3) Ti, Ti-5Ta and Zr showed excellent corrosion resistance in nitric acid with and without Plutonium and ruthenium. Especially, Ti and Ti-5Ta showed the improvement of corrosion resistance by co-existing Plutonium or ruthenium. It was explained by chemical stability of surface oxide film due to plutonium or ruthenium oxidant.
Wakai, Eiichi; Hishinuma, Akimichi; Usami, Koji; Kato, Yasushi*; Takaki, Seiichi*; Abiko, Kenji*
Materials Transactions, JIM, 41(9), p.1180 - 1183, 2000/09
no abstracts in English
Kato, Toshihiro*; ; ; ; Ishibashi, Yuzo; Takeda, Seiichiro
PNC TN8410 98-070, 31 Pages, 1998/02
None
Wakai, Eiichi; Hishinuma, Akimichi; Sawai, Tomotsugu; Kato, Yasushi*; Isozaki, Seiichi*; Takaki, Seiichi*; Abiko, Kenji*
Physica Status Solidi (A), 160(2), p.441 - 448, 1997/00
Times Cited Count：15 Percentile：66.71(Materials Science, Multidisciplinary)no abstracts in English
Wada, Yusaku; ; Kato, Shoichi; Seki, Seiichi
Residual Stresses - III, Vol.2, p.1519 - 1524, 1992/00
None
