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Journal Articles

Roles of excess minority carrier recombination and chemisorbed O$$_{2}$$ species at SiO$$_{2}$$/Si interfaces in Si dry oxidation; Comparison between p-Si(001) and n-Si(001) surfaces

Tsuda, Yasutaka; Yoshigoe, Akitaka; Ogawa, Shuichi*; Sakamoto, Tetsuya*; Yamamoto, Yoshiki*; Yamamoto, Yukio*; Takakuwa, Yuji*

Journal of Chemical Physics, 157(23), p.234705_1 - 234705_21, 2022/12

 Times Cited Count:0 Percentile:0.01(Chemistry, Physical)

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

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.

Journal Articles

Orbital magnetic moment and coercivity of SiO$$_2$$-coated FePt nanoparticles studied by X-ray magnetic circular dichroism

Takahashi, Yukio*; Kadono, Toshiharu*; Yamamoto, Shimpei*; Singh, V. R.*; Verma, V.*; Ishigami, Keisuke*; Shibata, Goro*; Harano, Takayuki*; Takeda, Yukiharu; Okane, Tetsuo; et al.

Physical Review B, 90(2), p.024423_1 - 024423_5, 2014/07

AA2015-0417.pdf:0.45MB

 Times Cited Count:10 Percentile:44.74(Materials Science, Multidisciplinary)

Journal Articles

Effect of water radiolysis on surface oxide film formed on SUS316L in $$gamma$$-ray irradiated high temperature water

Yamamoto, Masahiro; Kato, Chiaki; Sato, Tomonori; Nakahara, Yukio; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2013) (CD-ROM), 5 Pages, 2013/09

Major corrosion problems of light water reactor (LWR) which are represented by stress corrosion cracking are affected by dissolved oxygen (DO) concentration in feed water. Many corrosion tests were conducted with the parameter of DO values. Oxygen source of an actual LWR is radiolysis of cooling water and also H$$_{2}$$O$$_{2}$$ is generated. The effect of these species created by water radiolysis to corrosion of structural material was not sufficiently examined. $$gamma$$-ray irradiated experiments were conducted in high temperature water condition using type 316L stainless steels with crevice. The calculation of radiolysis products was not estimated by the effect of radiolysis products. From these results, much complicated reaction seemed to occur at the $$gamma$$-ray irradiated crevice portion.

Journal Articles

Interior textures, chemical compositions, and noble gas signatures of Antarctic cosmic spherules; Possible sources of spherules with long exposure ages

Osawa, Takahito; Yamamoto, Yukio*; Noguchi, Takaaki*; Iose, Akari*; Nagao, Keisuke*

Meteoritics & Planetary Science, 45(8), p.1320 - 1339, 2010/08

 Times Cited Count:12 Percentile:35.63(Geochemistry & Geophysics)

The interior texture and chemical and noble gas composition of 99 cosmic spherules collected from the meteorite ice field around the Yamato Mountains in Antarctica were investigated. Their textures were used to classify the spherules into six different types reflecting the degree of heating. An enigmatic spherule, labeled M240410, had an extremely high concentration of cosmogenic nuclides. Assuming 4$$pi$$ exposure to galactic and solar cosmic rays as a micrometeoroid and no exposure on the parent body, the cosmic-ray exposure (CRE) age of 393 Myr could be computed using cosmogenic $$^{21}$$Ne. Under these model assumptions, the inferred age suggests that the particle might have been an Edgeworth-Kuiper Belt object. Alternatively, if exposure near the surface of its parent body was dominant, the CRE age of 382 Myr can be estimated from the cosmogenic $$^{38}$$Ar using the production rate of the 2$$pi$$ exposure geometry, and implies that the particle may have originated in the mature regolith of an asteroid.

Journal Articles

Effects of $$gamma$$-ray irradiation and crevice-like shape on the corrosion of type 316L stainless steel in high-temperature water

Nakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Watanabe, Atsushi*; Fuse, Motomasa*

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2009 (CD-ROM), p.226 - 231, 2009/10

The irradiation effect to high-temperature water in nuclear power plant has been regarded as one of important issues for preventing corrosion and stress corrosion cracking of plant materials. However, the effects of surface reaction and configurations of material on irradiated high-temperature water chemistry have been studied little because of the difficulty of measuring the environment. In this work, we have done a series of corrosion tests of Type 316L stainless steel in high-temperature water in order to estimate the effects of $$gamma$$-ray irradiation and crevice-like shape on the water chemistry. Test specimens immersed in high-temperature water of 288 $$^{circ}$$C were $$gamma$$-ray irradiated for 500 hours. The absorbed dose rate of $$gamma$$-ray irradiation was estimated to be 30 kGy h$$^{-1}$$. The dimensions of the disk-like specimens were 16 mm in diameter by 0.5 mm in thickness. The surfaces of the specimens were mechanically finished with #800 emery paper. Sets of two specimens attached closely in order to simulate a crevice-like environment were also immersed. The surfaces of the specimens were analyzed using SEM, TEM, and laser Raman spectrometer. The results of surface analyses indicated that $$gamma$$-ray irradiation enhanced the precipitation of iron oxide on the surface and the thickness of inner oxide layer became thicker by $$gamma$$-ray irradiation. $$gamma$$-ray irradiation also changed the morphology of oxide on the surface faced to the crevice-like environment.

Journal Articles

Effects of $$gamma$$-ray irradiation on the high temperature oxidation of austenitic stainless steel in supercritical water

Nakahara, Yukio; Yamamoto, Masahiro; Karasawa, Hidetoshi*; Kiuchi, Kiyoshi; Katsumura, Yosuke*

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

Three types of commercial-grade austenitic stainless steel, Type 304L, Type 316L, and Type 310S, were immersed in deaerated supercritical water (SCW) of 25 MPa, 550 $$^{circ}$$C with $$gamma$$-ray irradiation for 1000 hours in total. Absorbed dose rates in SCW are estimated at 5-15 kGy h$$^{-1}$$. High temperature oxidation experiments resulted in the formation of two-layer oxide film in which the outer layer is porous iron oxide and the inner layer is dense iron-chromium-nickel oxide. Rate constants of parabolic rate law in net weight gains of Type 304L SS and Type 310S SS are decreased as the $$gamma$$-ray exposure rate is increased. The net weight gain of $$gamma$$-ray irradiated Type 316L SS is sharply fluctuating and decreasing, because the flaking of the outer layer occurred. Hematite is formed in the outer layer on all irradiated samples of examined alloys. The concentration of chromium on the surface is increased by $$gamma$$-ray irradiation. A chromium-rich part in the inner layer accompanying a nickel-rich part in the metal is formed along to the oxide/metal interface of $$gamma$$-ray irradiated Type 304L SS, non-irradiated and $$gamma$$-ray irradiated Type 316L SS.

Journal Articles

Effects of radiation-induced stress relaxation on radiation hardening and IASCC Susceptibility in type 316L stainless steel in BWR condition

Miwa, Yukio; Kaji, Yoshiyuki; Tsukada, Takashi; Yamamoto, Toshio; Kato, Yoshiaki; Yonekawa, Minoru; Matsui, Yoshinori

Proceedings of 15th International Conference on Nuclear Engineering (ICONE-15) (CD-ROM), 6 Pages, 2007/04

Radiation-induced stress relaxation (RISR) test under uniaxial loading condition for tensile type specimens was carried out for type 316L stainless steel (SS). The specimens were irradiated in the Japan Materials Testing Reactor at 561 K to three dose levels (0.1-3 dpa) under four displacement constrained condition (prestrain range; 0.06-0.75%) in order to apply residual stress. Radiation hardening behavior and IASCC susceptibility of the RISR-tested 316L SS were examined by slow strain rate testing (SSRT) in oxygenated high temperature water. It was concluded from the SSRT results that the RISR had little influence on the radiation hardening behavior and IASCC susceptibility in the 316L SS. In all specimens, the residual stress rapidly decreased with increasing dose, and the residual stress level after irradiation was much lower than the stress level to initiate IASCC.

Journal Articles

Crystal and magnetic structures and their temperature dependence of Co$$_{2}$$Z-type hexaferrite (Ba, Sr)$$_{3}$$Co$$_{2}$$Fe$$_{24}$$O$$_{41}$$ by high-temperature neutron diffraction

Takada, Yukio*; Nakagawa, Takashi*; Tokunaga, Masatoshi*; Fukuta, Yasunari*; Tanaka, Takayoshi*; Yamamoto, Takao*; Tachibana, Takeshi*; Kawano, Shinji*; Ishii, Yoshinobu; Igawa, Naoki

Journal of Applied Physics, 100(4), p.043904_1 - 043904_7, 2006/08

 Times Cited Count:69 Percentile:89.28(Physics, Applied)

no abstracts in English

Journal Articles

Temperature dependence of magnetic moment orientation in Co$$_{2}$$Z-type hexaferrite estimated by high-temperature neutron diffraction

Takada, Yukio*; Nakagawa, Takashi*; Fukuta, Yasunari*; Tokunaga, Masatoshi*; Yamamoto, Takao*; Tachibana, Takeshi*; Kawano, Shinji*; Igawa, Naoki; Ishii, Yoshinobu

Japanese Journal of Applied Physics, 44(5A), p.3151 - 3156, 2005/05

 Times Cited Count:3 Percentile:13.72(Physics, Applied)

We investigated the correlation between the thremomagnetic curve of Co$$_{2}$$Z-Type hexagonal barium ferrite, Ba$$_{3}$$Co$$_{1.8}$$Fe$$_{24.2}$$O$$_{41}$$ and its magnetic moment direction. The thermomagnetic curve shows two significant magnetization slumps at 540K and 680K. High-temperature neutron diffraction experiment and Rietveld analyses indicate that temperature rise from 523 to 573K makes the magnetic moments turn to the c-axis from a direction parallel to the c-plane most significantly.The change in average orientation of the magnetic moments must be induced by the disappearence of the contribution of cobalt to magnetism in this temperature.

Journal Articles

Electron acceleration by a nonlinear wakefield generated by ultrashort (23-fs) high-peak-power laser pulses in plasma

Kando, Masaki; Masuda, Shinichi; Zhidkov, A.*; Yamazaki, Atsushi; Kotaki, Hideyuki; Kondo, Shuji; Homma, Takayuki*; Kanazawa, Shuhei; Nakajima, Kazuhisa; Hayashi, Yukio; et al.

Physical Review E, 71(1), p.015403_1 - 015403_4, 2005/01

 Times Cited Count:33 Percentile:77.43(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Improvement of critical heat flux correlation for research reactors using plate-type fuel

Kaminaga, Masanori; Yamamoto, Kazuyoshi; Sudo, Yukio

Journal of Nuclear Science and Technology, 35(12), p.943 - 951, 1998/12

 Times Cited Count:21 Percentile:83.26(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Irradiation effects on plasma diagnostic components

Nishitani, Takeo; *; Ikeda, Yujiro; Ishitsuka, Etsuo; Kakuta, Tsunemi; Kasai, Satoshi; Kawamura, Hiroshi; Morita, Yosuke; Nagashima, Akira; Nakamichi, Masaru; et al.

JAERI-Research 98-053, 105 Pages, 1998/10

JAERI-Research-98-053.pdf:4.78MB

no abstracts in English

Journal Articles

Improvement of CHF correlations for research reactors using plate-type fuels

Kaminaga, Masanori; Yamamoto, Kazuyoshi; Sudo, Yukio

Proceedings of 8th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-8), Vo.3, p.1815 - 1822, 1997/00

In research reactors, plate-type fuel elements are generally adopted so as to produce high power densities and are cooled by a downward flow. A core flow reversal from a steady-state forced downward flow to an upward flow due to natural convection should occur during operational transients such as "Loss of the primary coolant flow". Therefore, in the thermal hydraulic design of research reactors, critical heat flux (CHF) under a counter-current flow limitation (CCFL) or a flooding condition are important to determine safety margins of fuel against CHF during a core flow reversal. The authors have proposed a CHF correlation scheme for the thermal hydraulic design of research reactors, based on CHF experiments for both upward and downward flows including CCFL condition. When the CHF correlation scheme was proposed, a subcooling effect for CHF correlation under CCFL condition had not been considered because of a conservative evaluation and a lack of enough CHF data to determine the subcooling effect on CHF. A too conservative evaluation is not appropriate for the design of research reactors because of construction costs etc. Also, conservativeness of the design must be determined precisely. In this study, therefore, the subcooling effect on CHF under the CCFL conditions in vertical rectangular channels heated from both sides were investigated quantitatively based on CHF experimental results obtained under uniform and nonuniform heat flux condition. As a result, it was made clear that CHF in this region increase linearly with an increase of the channel inlet subcooling and a new CHF correlation including the effect of channel inlet subcooling was proposed.

JAEA Reports

Evaluation of FP behavior and O/M ratio in FBR fuel irradiated to high burnup

Sato, Isamu; Yamamoto, Kazuya; Kajitani, Yukio

PNC TN9410 96-251, 82 Pages, 1996/06

PNC-TN9410-96-251.pdf:8.28MB

The O/M ratio of fuel is related with most of fuel properties, especially it is important to evaluate radial O/M ratio distribution of fuel irradiated to high burnup in order to predict change of the properties. In this work, the radial O/M ratio distribution of irradiated FBR fuels was measured and evaluated. The fuels are irradiated in "JOYO", which were irradiated to the highest burnup(ca. 13at%). In this study, an indirect method, REDOX of Mo was used to obtain radial O/M ratio distribution, in which oxygen potential in fuel was determined by measuring oxidation and reduction states of Mo existing as a fission product (FP) in fuel. Oxygen potential distribution in fuel was determined from temperature profile and measured Mo distribution in fuel. O/M ratio distribution in fuel was evaluated from the oxygen potential, based on Catlow theory. The obtained O/M ratio distribution in fuel was compared with one calculated using Aitken model, which explains oxygen migration in fuel. Consequently, it was shown that the oxygen migration mechanism in high burnup fuel might differ from one suggested by Aitken and it might be necessary to take into consideration the effect of burnup on heat oftransport in oxygen thermal diffusion.

JAEA Reports

None

Wada, Yukio; Funasaka, Hideyuki; Myochin, Munetaka; Yamamoto, Kazunori; Harada, Hideo; ;

PNC TN8100 96-005, 16 Pages, 1996/01

PNC-TN8100-96-005.pdf:1.6MB

no abstracts in English

Journal Articles

Design of the ITER central solenoid scalable model coil

Yamamoto, Keiichi*; Yoshida, Kiyoshi; Yasukawa, Yukio*; Tsukamoto, Hideo*; Sasaki, Takashi*; Okuno, Kiyoshi; Nishi, Masataka; Koizumi, Norikiyo; Isono, Takaaki; Sugimoto, Makoto; et al.

Proc. of the 17th Symp. on Fusion Technology, 0, p.971 - 975, 1993/00

no abstracts in English

JAEA Reports

None

Kato, Masato; Sakurai, Koji*; Kano, Yoshiharu*; Funasaka, Hideyuki; Yamamoto, Kazunori; *; Wada, Yukio

PNC TN8410 92-060, 7 Pages, 1992/03

PNC-TN8410-92-060.pdf:0.24MB

None

JAEA Reports

Design of operation and maintenance management support system for JOYO

Sato, Masuo*; Fukawa, Naohiro*; Tamaoki, Tetsuo*; Takahashi, Hideji*; Ito, Atsushi*; Yoshida, Megumi*; Sonoda, Yukio*; Yamamoto, Kazuhiko*; Maruyama, Fumi*

PNC TJ9164 89-003, 200 Pages, 1989/03

PNC-TJ9164-89-003.pdf:5.83MB

In nuclear power plant, we need to realize the computerization for the management of the plant operation and maintenance. Especially, in a periodic inspection, lots of works are concentrated. A great deal of man power is required for examining the permission of works, publishing the component isolation tags and making or revising the documents to control the schedules. Recently, in Light Water Reactor, a lot or computerization systems are developed. We design the plant management system in consideration of the characteristics of a Fast Breeder Reactor. We embody the softwear methods and hardwear systems widely to systematize the plant management technology that is accumulated at the experimental reactor JOYO. We can expect an economization and an inprovment of realiability and efficiency of the plant management.

48 (Records 1-20 displayed on this page)