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Journal Articles

Sintering and microstructural behaviors of mechanically blended Nd/Sm-doped MOX

Hirooka, Shun; Horii, Yuta; Sunaoshi, Takeo*; Uno, Hiroki*; Yamada, Tadahisa*; Vauchy, R.; Hayashizaki, Kohei; Nakamichi, Shinya; Murakami, Tatsutoshi; Kato, Masato

Journal of Nuclear Science and Technology, 60(11), p.1313 - 1323, 2023/11

 Times Cited Count:1 Percentile:96.85(Nuclear Science & Technology)

Additive MOX pellets are fabricated by a conventional dry powder metallurgy method. Nd$$_{2}$$O$$_{3}$$ and Sm$$_{2}$$O$$_{3}$$ are chosen as the additive materials to simulate the corresponding soluble fission products dispersed in MOX. Shrinkage curves of the MOX pellets are obtained by dilatometry, which reveal that the sintering temperature is shifted toward a value higher than that of the respective regular MOX. The additives, however, promote grain growth and densification, which can be explained by the effect of oxidized uranium cations covering to a pentavalent state. Ceramography reveals large agglomerates after sintering, and Electron Probe Micro-Analysis confirms that inhomogeneous elemental distribution, whereas XRD reveals a single face-centered cubic phase. Finally, by grinding and re-sintering the specimens, the cation distribution homogeneity is significantly improved, which can simulate spent nuclear fuels with soluble fission products.

Journal Articles

A Storm-induced flood and associated nearshore dispersal of the river-derived suspended $$^{137}$$Cs

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

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

Uniaxial strain dependence of the critical current of DI-BSCCO tapes

Osamura, Kozo*; Machiya, Shutaro*; Hampshire, D. P.*; Tsuchiya, Yoshinori*; Shobu, Takahisa; Kajiwara, Kentaro*; Osabe, Goro*; Yamazaki, Kohei*; Yamada, Yuichi*; Fujikami, Jun*

Superconductor Science and Technology, 27(8), p.085005_1 - 085005_11, 2014/08

 Times Cited Count:27 Percentile:74.87(Physics, Applied)

Journal Articles

Ion beam analysis of quaternary Heusler alloy Co$$_{2}$$(Mn$$_{1-x}$$Fe$$_{x}$$)Si(111) epitaxially grown on Ge(111)

Kawakubo, Yuki*; Noguchi, Masaya*; Hirata, Tomoaki*; Narumi, Kazumasa; Sakai, Seiji; Yamada, Shinya*; Hamaya, Kohei*; Miyao, Masanobu*; Maeda, Yoshihito

Physica Status Solidi (C), 10(12), p.1828 - 1831, 2013/12

 Times Cited Count:0 Percentile:0.01

Journal Articles

The Role of ${it Deinococcus radiodurans}$ RecFOR proteins in homologous recombination

Sato, Katsuya; Kikuchi, Masahiro; Ishaque, A. M.*; Oba, Hirofumi*; Yamada, Mitsugu; Tejima, Kohei; Onodera, Takefumi; Narumi, Issei

DNA Repair, 11(4), p.410 - 418, 2012/04

 Times Cited Count:23 Percentile:60.06(Genetics & Heredity)

In an effort to gain insights into the role of ${it D. radiodurans}$ RecFOR proteins in homologous recombination, we generated ${it recF}$, ${it recO}$ and ${it recR}$ disruptant strains and characterized the disruption effects. Disruption of ${it recR}$ resulted in severe reduction of the transformation efficiency. On the other hand, the ${it recF}$ disruptant strain was the most sensitive phenotype to $$gamma$$ rays, UV irradiation and mitomycin C among the three disruptants. In the ${it recF}$ disruptant strain, the intracellular level of the LexA1 protein did not decrease following $$gamma$$ irradiation. These results demonstrate that the RecF protein plays a crucial role in the homologous recombination repair process by facilitating RecA activation. Thus, the RecF and RecR proteins are involved in the RecA activation and the stability of incoming DNA, respectively, during RecA-mediated homologous recombination processes that initiated the ESDSA pathway in ${it D. radiodurans}$.

Journal Articles

"Crystal lattice engineering", an approach to engineer protein crystal contacts by creating intermolecular symmetry; Crystallization and structure determination of a mutant human RNase 1 with a hydrophobic interface of leucines

Yamada, Hidenori*; Tamada, Taro; Kosaka, Megumi*; Miyata, Kohei*; Fujiki, Shinya*; Tano, Masaru*; Moriya, Masayuki*; Yamanishi, Mamoru*; Honjo, Eijiro; Tada, Horiko*; et al.

Protein Science, 16(7), p.1389 - 1397, 2007/07

 Times Cited Count:39 Percentile:59.73(Biochemistry & Molecular Biology)

In an attempt to control protein incorporation in a crystal lattice, a leucine zipper-like hydrophobic interface (comprising four leucine residues) was introduced into a helical region (helix 2) of the human pancreatic ribonuclease 1 (RNase 1) that was predicted to form a suitable crystallization interface. Although crystallization of wild type RNase 1 has not yet been reported, the RNase 1 mutant having four leucines (4L-RNase 1) was successfully crystallized under several different conditions. The crystal structures were subsequently determined by X-ray crystallography by molecular replacement using the structure of bovine RNase A. The overall structure of 4L-RNase 1 is quite similar to that of the bovine RNase A, and the introduced leucine residues formed the designed crystal interface. To further characterize the role of the introduced leucine residues in crystallization of RNase 1, the number of leucines was reduced to three or two (3L- and 2L-RNase 1, respectively). Both mutants crystallized and a similar hydrophobic interface as in 4L-RNase 1 was observed. A related approach to engineer crystal contacts at helix 3 of RNase 1 (N4L-RNase 1) was also evaluated. N4L-RNase 1 also successfully crystallized, and formed the expected hydrophobic packing interface. These results suggest that appropriate introduction of a leucine zipper-like hydrophobic interface can promote intra molecular symmetry for more efficient protein crystallization in crystal lattice engineering efforts.

Oral presentation

Development of fuel design system for BWR composed of open computer code, 3

Yoshikawa, Takamichi*; Iwasaki, Tomohiko*; Endo, Hideki*; Suyama, Kenya; Shikoda, Keiji*; Yamada, Kohei*; Hamahata, Yoshiki*; Oeda, Shin*

no journal, , 

In order to develop a fuel design system of BWR based on opened calculation codes, a burnup code system SWAT2 using continuous energy Mote Carlo code was revised to include a function of branch calculation. A tool to evaluate lattice constants used in calculation code adopting modern nodal method was also developed and validated by comparison with CASMO.

Oral presentation

An Experimental study of host rock alteration due to hyperalkaline pore water

Yamaguchi, Kohei; Oda, Chie; Nakazawa, Toshiyuki*; Yamada, Norikazu*; Takase, Toshio*

no journal, , 

In this research, the batch immersion experiment and the flow-through column experiment of granite and the artificial highperalkaline pore water were conducted, and the main geochemistry reaction was examined. A change with the lapse of time of the saturation index was calculated by the chemical equilibrium computation based on the batch immersion experiment result. The secondary mineral with the possibility of precipitation in the liquid phase based on the calculation result was extracted, and the combination was examined. In addition, the combination of these secondary minerals was applied to the flow-through column experiment result, and the liquid phase composition after the flow-through and the secondary mineral's spatial distribution were compared with geochemistry calculation (PHREEQC) result. As a result, it has been understood to have to understand the main geochemistry reaction paying attention at the precipitation rate of the secondary mineral in the future.

Oral presentation

For realization of the vibration simulation of the nuclear power plant scale

Nakajima, Norihiro; Yamada, Tomonori; Nakajima, Kohei; Nishida, Akemi; Suzuki, Yoshio; Araya, Fumimasa; Kushida, Noriyuki

no journal, , 

no abstracts in English

Oral presentation

An Experimental study and modeling of host rock alteration due to hyperalkaline pore water

Yamaguchi, Kohei; Oda, Chie; Nakazawa, Toshiyuki*; Yamada, Norikazu*; Takase, Toshio*

no journal, , 

High alkaline pore water runs out from a large amount of cementitious material used for the TRU waste disposal to the host rock, and there is a possibility that the migration characteristic of the nuclide. Here, the applicability of a chemical model in the environment with water flow was evaluated by the viewpoint of the solution composition and the precipitation composition by conducting the experiment that passed high alkaline solution to the column. As a result, a change with the lapse of time of the concentration was able to be reproduced almost for the solution composition. Moreover, the precipitation of Al was not able to be reproduced though Ca and Si were able to be wide in the column. The thermodynamics data of the secondary mineral including Al, the maintenance of the precipitation rate, and the applicability examination to the experiment result etc. are profitable as future tasks.

Oral presentation

Importance of RecFOR in homologous recombination mechanism in ${it Deinococcus radiodurans}$

Sato, Katsuya; Kikuchi, Masahiro; Oba, Hirofumi*; Yamada, Mitsugu; Tejima, Kohei; Onodera, Takefumi; Narumi, Issei

no journal, , 

In an effort to gain an insight into the role of the RecFOR in DNA repair through homologous recombination in ${it Deinococcus radiodurans}$, we generated a RecFOR disruptant strains and characterized the disruption effects. The RecF disruptant strain exhibited sensitivity to DNA-damaging agents, suggesting that RecF has a crucial role in DNA repair. This result indicates that RecF takes an important role in the RecA activation in the homologous recombination process with DNA damage. While, the recombination assay revealed that RecR is essential for the process of homologous intermolecular recombination, suggesting that RecR is important factor in the homologous recombination process without DNA damage. The importance of RecF and RecR in the homologous recombination processes is reversed due to the existence of DNA damage. Therefore, ${it D. radiodurans}$ will use the different homologous recombination processes through the RecFOR or RecOR, respectively.

Oral presentation

Spectral characteristics of asteroid (162173) Ryugu with Hayabusa2 NIRS3

Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.

no journal, , 

JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.

Oral presentation

Manufacturing and property measurements of homogeneous simulated FP (Nd/Sm/Gd/Zr)-doped MOX

Horii, Yuta; Hirooka, Shun; Vauchy, R.; Hayashizaki, Kohei; Uno, Hiroki*; Tamura, Tetsuya*; Sunaoshi, Takeo*; Ohwada, Hideaki*; Yamada, Tadahisa*; Murakami, Tatsutoshi

no journal, , 

Fission products (FPs), which are generated and stored in fuel matrix by irradiating nuclear fuels, affect thermo-physical fuel properties. To improve accuracy of computer simulation of irradiation behaviors, studies on the fuel properties containing FPs are needed. However, only a limited number of studies on the irradiated fuel properties, especially MOX fuels, have been reported in the world due to difficulties in handling of the irradiated fuels. Moreover, the effect of individual FP cannot be evaluated because many kinds of FPs are stored in the irradiated fuels. Thus, an alternative method should be suggested to easily study the effects of FPs on the fuel properties. In this study, fuel properties were measured to evaluate the effects of FPs by using simulated FP-doped MOX specimens instead of a real irradiated fuel. For the measurement, the homogeneity of FP in a specimen is also important, as well as uranium and plutonium. To obtain homogeneous specimens, re-grinding and re-sintering processes were repeated and the improvement was confirmed by EPMA and XRD at each set of the process. A specimen with suitable homogeneity for measurement was prepared by repeating the series of processes three times. Sm$$_{2}$$O$$_{3}$$, Gd$$_{2}$$O$$_{3}$$ and ZrO$$_{2}$$, which are major and soluble FPs in irradiated MOX fuels, were selected as simulated FPs. The effect of individual FP on the properties, such as thermal conductivity and thermal expansion, was evaluated on the specimens. In addition, Nd$$_{2}$$O$$_{3}$$, Sm$$_{2}$$O$$_{3}$$ and Gd$$_{2}$$O$$_{3}$$ co-doped MOX was also prepared to compare the influence of containing multiple lanthanides.

Oral presentation

Manufacturing of homogeneous simulated FPs (Nd$$_{2}$$O$$_{3}$$/Sm$$_{2}$$O$$_{3}$$/Gd$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$)-doped MOX for studies on MOX fuel properties

Horii, Yuta; Hirooka, Shun; Vauchy, R.; Hayashizaki, Kohei; Uno, Hiroki*; Tamura, Tetsuya*; Sunaoshi, Takeo*; Ohwada, Hideaki*; Yamada, Tadahisa*; Murakami, Tatsutoshi

no journal, , 

Fission products (FPs), which are generated and stored in the fuel matrix by irradiating MOX fuels, affect the fuel properties. In previous studies, many properties of unirradiated MOX were reported. On the other hand, the number of studies on irradiated MOX properties are limited. Studying properties of irradiated materials has difficulties in handling, therefore, using simulated FP-doped (U,Pu)O$$_{2}$$ is an alternative method in studying irradiated fuel properties. In order to evaluate the effect of simulated FPs, the homogeneity is one of the important factors. In this study, two dry-processing methods, namely melting and grinding-mixing methods, respectively, are employed and evaluated the aptitude as methods to prepare the homogeneous simulated FP-doped (U,Pu)O$$_{2}$$.

Oral presentation

Differences in extraction mechanisms between fluorous and organic extraction systems; Structuring extractants at the interface and in the bulk extracting phase

Ueda, Yuki; Micheau, C.; Motokawa, Ryuhei; Tokunaga, Kohei; Akutsu, Kazuhiro*; Yamada, Norifumi*

no journal, , 

no abstracts in English

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