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Journal Articles

Major element and REE compositions of Pliocene sediments in southwest Japan; Implications for paleoweathering and paleoclimate

Hatano, Nozomi*; Yoshida, Koki*; Mori, Saori*; Sasao, Eiji

Sedimentary Geology, 408, p.105751_1 - 105751_13, 2020/10

The history of the East Asian monsoon and the relationship between the development of the monsoon climate, tectonics and global climate are complicated and controversial. The present study clarifies the chemical weathering conditions in southwest Japan based on the concentrations of major elements and rare earth elements (REEs) in lacustrine muddy sediments. Between 3.8 and 3.4 Ma, chemical weathering significantly intensified, as indicated by the high values of the chemical index of alteration as well as the high concentrations of REEs and light REEs against heavy REEs and kaolinite-rich clay mineral compositions. The intense chemical weathering on land in southwest Japan from 3.8 to 3.4 Ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the Kuroshio Current and the intensification of the East Asian summer monsoon.

Journal Articles

Intense chemical weathering in southwest Japan during the Pliocene warm period

Hatano, Nozomi*; Yoshida, Koki*; Adachi, Yoshiko*; Sasao, Eiji

Journal of Asian Earth Sciences, 184, p.103971_1 - 103971_13, 2019/10

 Times Cited Count:1 Percentile:68.98(Geosciences, Multidisciplinary)

Whole rock major and REE geochemistry and mineral compositions of the Pliocene sediments in southwest Japan reveal the effects of source rock compositions and grain sizes, as well as the relationship between sedimentary environments and the degree of chemical weathering in the Pliocene warm period. A wide variation in the degree of chemical weathering, source rock compositions and grain sizes were observed with vertical and spatial changes in the sedimentary environment. Regardless of the wide variety of source rock compositions and grain sizes, REE and kaolinite-rich clay mineral concentrations in sediments, of which CIA values are generally above 90, are indicative of the intense weathering conditions that prevailed in the Pliocene period (3-4 Ma) in southwest Japan.

Journal Articles

Fracture characterization and rock mass behavior induced by blasting and mechanical excavation of shafts in Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Sato, Toshinori; Hayano, Akira

Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.682 - 687, 2019/05

In high-level radioactive disposal projects, it is important to investigate the extent of the excavation damaged zone (EDZ) for safety assessment because EDZ can provide a migration pathway for radionuclides from the facility. To investigate the quantitative differences between EDZs formed because of blasting and mechanical excavation, we studied the characteristics of fractures induced by excavation based on fracture mapping performed during shaft sinking (V- and E-Shafts). As a result, it was found that blasting excavation can lead to the formation of a large number of newly created fractures (EDZ fractures) compared with mechanical excavation. In addition, the seismic velocity (P-wave velocity) measured during blasting excavation (E-Shaft) was lower than that measured during mechanical excavation (V-Shaft). Furthermore, we found that the support pattern that reinforces forward rocks to be appropriate for limiting damage to the shaft wall.

Journal Articles

Effects of grain size on the chemical weathering index; A Case study of Neogene fluvial sediments in southwest Japan

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji

Sedimentary Geology, 386, p.1 - 8, 2019/05

 Times Cited Count:2 Percentile:36.53(Geology)

Grain size variation of sediments generally complicates the assessment of the degree of chemical weathering. Mineralogical and geochemical research was carried out on Miocene and Pliocene fluvial sediments in southwest Japan to evaluate the effects of grain size on the degree of chemical weathering. We indicated that the Al$$_{2}$$O$$_{3}$$/SiO$$_{2}$$ ratio may be suitable as a grain size index. Most of the fine-grained sediments have higher CIA values. In contrast, coarse-grained sediments, display a wide range of CIA values. The CIA values for intermediate grain sized samples reflect distinctive differences in the degree of chemical weathering between Miocene and Pliocene sediments. In the intermediate grain sized samples, the Miocene sediments have higher CIA values than Pliocene sediments. To compare the degree of chemical weathering, it is desirable to evaluate with the Al$$_{2}$$O$$_{3}$$/SiO$$_{2}$$ ratios limited to the intermediate grain size range.

Journal Articles

Fracture characterization and rock mass damage induced by different excavation methods in the Horonobe URL of Japan

Tokiwa, Tetsuya*; Tsusaka, Kimikazu*; Aoyagi, Kazuhei

International Journal of Civil Engineering, 16(4), p.371 - 381, 2018/04

 Times Cited Count:1 Percentile:84.11(Engineering, Civil)

Journal Articles

A Study of efficient excavation limiting the extent of an excavation damaged zone in Horonobe URL

Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Fujita, Tomoo

Rock Mechanics and Rock Engineering; From the Past to the Future (EUROCK 2016), p.1023 - 1028, 2016/07

Journal Articles

Excavation damaged zone inferred by geophysical surveys on drift floor of Horonobe URL

Tokiwa, Tetsuya*; Aoyagi, Kazuhei; Fujita, Tomoo

Rock Mechanics and Rock Engineering; From the Past to the Future (EUROCK 2016), p.901 - 906, 2016/07

Journal Articles

A Study on optimum irradiation dose of $$gamma$$-ray and carbon ion beams in grain amaranth

Nemoto, Kazuhiro*; Tsurukawa, Akiko*; Minami, Mineo*; Matsushima, Kenichi*; Hase, Yoshihiro

JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 112, 2015/03

no abstracts in English

Journal Articles

Effect of heavy ion irradiation to the silkworm eggs at before fertilization and at nuclear cleavage stage

Ueda, Daisuke*; Shirai, Koji*; Funayama, Tomoo; Sakashita, Tetsuya; Yokota, Yuichiro; Kobayashi, Yasuhiko

JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 84, 2015/03

In this study, we investigated the effects of irradiation to the silkworm eggs at various developmental stages. First, we tried the irradiation to the unfertilized eggs (at 1.5 hour after oviposition). At this stage, the female pronucleus and the sperm nucleus are observed in the eggs, but not fertilized. After irradiation, the irradiated eggs stopped the development after fertilization. About 2 hours after, the egg restarted the nuclear cleavage. This result indicates the DNA damage on pronuleus cannot prevent the fertilization. We also investigated the effects of irradiation to the egg at the nuclear cleavage stage (at 6 hour after oviposition). The egg also stopped the development after irradiation, but the duration time of the developmental arrest was almost two times longer (about 4 hours) than that of the egg irradiated at fertilization.

Journal Articles

Velocity of entrainments formed by high velocity air jet flow in stagnant water

Akabane, Masaaki*; Koizumi, Yasuo; Uchibori, Akihiro; Kamide, Hideki; Ohshima, Hiroyuki

Proceedings of 22nd International Conference on Nuclear Engineering (ICONE-22) (DVD-ROM), 6 Pages, 2014/07

A liquid droplet entrainment which appears under heat transfer tube failure accident in a steam generator of sodium-cooled fast reactors and causes wastage on an adjacent tube was examined in this study. The visualization experiment on a high-pressure air jet in a liquid pool was carried out. Filament-like ears and wisps pulled out from the wavy gas-liquid interface were observed. The ears and the wisps were broken off and entrained into the air jet. This process seems quite similar to the entrainment process in an annular dispersed flow in a pipe. The velocity of the entrained droplet was estimated from an image processing. The axial velocity of the entrained droplet increased as the air jet velocity increased. The Transversal directional velocity was much slower than the axial directional velocity. The data obtained from this experiment are very useful for the study of the heat transfer tube failure accident.

Journal Articles

Effect of physical properties on gas entrainment rate from free surface by vortex, 2

Koizumi, Yasuo*; Ote, Naosuke*; Kamide, Hideki; Ohno, Shuji; Ito, Kei

Proceedings of 22nd International Conference on Nuclear Engineering (ICONE-22) (DVD-ROM), 7 Pages, 2014/07

Journal Articles

Entrainment into high speed air jet blowing out from a hole to stagnant water

Koizumi, Yasuo*; Nago, Kohei*; Uchibori, Akihiro; Kamide, Hideki; Ohshima, Hiroyuki

Proceedings of ASME 2013 International Mechanical Engineering Congress and Exposition (IMECE 2013) (DVD-ROM), 6 Pages, 2013/11

Flow visualization experiments of an air jet in liquid were performed. The air jet was blown vertically upward into stagnant water or kerosine in the test vessel from a 1 mm width nozzle which was located at the bottom of the test vessel. A flow state of the jet in the liquid was recorded with a high speed video camera. Experimental result showed that the filament-like ears and wisps were pulled out from the wavy interface between liquid and the air jet. The ears and wisps were broken off and entrained into the air jet. As the air jet velocity increased, the number of entrainments created by the air jet increased lineally. The correlation for the entrainment diameter distribution which was developed for the annular dispersed two-phase flow in a pipe predicted well the present results. Measured entrainment rates were considerably lower than the prediction of the correlation for the annular dispersed two-phase flow in a pipe.

Journal Articles

Effect of physical properties on gas entrainment rate from free surface by vortex

Ote, Naosuke*; Koizumi, Yasuo*; Kamide, Hideki; Ohno, Shuji; Ito, Kei

Proceedings of 21st International Conference on Nuclear Engineering (ICONE-21) (DVD-ROM), 7 Pages, 2013/07

A sodium-cooled fast breeder reactor is now at the developing stage in Japan. One concern for safety is cover gas entrainment into the sodium coolant. The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Liquid flowed into a cylindrical vessel from a wall tangentially. Swirl flow was formed in the vessel, and then liquid drained from the bottom outlet of the vessel. A hollow vortex was formed on the free surface in the test vessel. Air was entrained under the free surface of the vortex and carried away from the bottom of the vessel. The flow state of the gas entrainment was visually observed by using a high speed video camera. The gas entrainment rate into liquid was measured. In the previous study, test fluid was water. Kerosene and 20 cSt silicone oil were newly introduced as the test fluid to examine the effect of the physical properties on the gas entrainment phenomena.

Journal Articles

Gas entrainment rate from free surface by vortex

Koizumi, Yasuo*; Ote, Naosuke*; Kamide, Hideki; Ohno, Shuji; Ito, Kei

Proceedings of 6th Japanese-European Two-Phase Flow Group Meeting (USB Flash Drive), 6 Pages, 2012/09

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Water, 20 cSt silicone oil and kerosene were used as test fluid in the experiments. When the liquid flow rate was low, small air bubbles were torn off from the vortex tip. The torn-off bubble flow rate was small. The gas entrainment increased drastically with the increase of the liquid flow rate. When the liquid level height in the vessel was low, only the latter type of the gas entrainment was observed. As the liquid level was increased, the former type was observed first and then the entrainment turned to the latter type. The physical properties of the viscosity and the surface tension had some effect on gas entrainment phenomena such as the gas entrainment rate and the initiation of the gas entrainment. The Kelvin-Helmholtz instability seemed to explain the inception of the bubble type and also the vortex type entrainment.

Journal Articles

Visualization of entrainment and surface behavior of high speed air jet blowing out from a hole to stagnant water

Nago, Kohei*; Koizumi, Yasuo*; Uchibori, Akihiro; Ohshima, Hiroyuki

Proceedings of 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference (ICONE-20 & POWER 2012) (DVD-ROM), 6 Pages, 2012/07

The experiment on a two dimensional air jet in a thin vessel filled with water was carried out to investigate the behavior of the jet interface and liquid droplet entrainment. The air jet in the water was recorded with a high speed video camera. The recorded photos showed that the filament-like ears and wisps were pulled out from the wavy water surface and the droplets were entrained. Droplet diameters and entrainment rate were obtained from the recorded photos. As the air velocity increased, the number of droplets increased lineally and the smaller droplets increased. The correlation for the droplet diameter distribution developed for the annular dispersed two-phase flow in a pipe predicted well the present experimental results. The correlations for the gas jet in the liquid pool underestimated the experimental results.

Journal Articles

Measurement of gas entrainment rate from free surface by vortex

Koizumi, Yasuo*; Ote, Naosuke*; Kamide, Hideki; Ohno, Shuji; Ito, Kei

Proceedings of 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference (ICONE-20 & POWER 2012) (DVD-ROM), 5 Pages, 2012/07

A sodium-cooled fast breeder reactor is now at the developing stage in Japan. One concern for safety is cover gas entrainment into the sodium coolant. The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. In the present experiments, test fluid was changed from water in the previous experiments to 20 cSt silicone oil. The liquid level in the test vessel was 25 mm in the present experiments. Only the vortex-type gas-entrainment was observed as in the previous experiments since the liquid level was low. The flow state observed at the flow visualization section of the outlet pipe was only a semi-annular flow. The initiation of the gas entrainment was delayed in the case of silicone oil compared with the case of water. The increasing rate of the gas entrainment to the liquid velocity is milder in the case of silicone oil than in the case of water.

Journal Articles

Bubble-type gas entrainment into liquid from free surface by vortex

Ikoma, Yusuke*; Koizumi, Yasuo*; Ito, Kei; Ohshima, Hiroyuki

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 8 Pages, 2011/10

A gas entrainment rate into liquid by a vortex formed on the free surface was examined experimentally. When the flow velocity was low, a single bubble was periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. An increase in the flow velocity resulted in the transition from the bubble-type gas entrainment to the vortex-type gas entrainment and the gas entrainment rate considerably increased with the flow velocity. After the vortex tip penetrated into the outlet pipe, the rotation speed of the vortex decayed. As a result of it, the Kelvin-Helmholtz instability wave length got long and the size of the generated bubble became large. Then, the outlet pipe was filled with the large bubbles and the flow state in the outlet pipe turned to the slug/churn flow and a large amount of gas began to be carried out form the test vessel.

Journal Articles

Application of high-precision numerical simulation method to quantitative evaluation of gas entrainment phenomena

Ito, Kei; Koizumi, Yasuo*; Ohshima, Hiroyuki; Kawamura, Takumi*

Dai-16-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, p.219 - 222, 2011/06

Gas entrainment (GE) phenomena in fast reactors have to be evaluated in terms of their occurrences because entrained bubbles in the primary cooling system may cause disturbances in reactor power. In fast reactors, a small amount of entrained gas may be allowed because there are always small deposition bubbles in the primary cooling system. In this case, not only the GE occurrences but also the amount of the entrained gas should be evaluated accurately. Therefore, the authors are studying the amount of the entrained gas by utilizing simple an experiment and a numerical simulation. In this paper, parametric simulations of the simple experiment are performed with a high-precision volume-of-fluid algorithm which simulate interfacial dynamic deformations directly. As a result, the simulation results gives larger entrained gas flow rate than the experimental data but the dependency of the entrained gas flow rate on the liquid flow rate is reproduced qualitatively.

Journal Articles

Quantitative evaluation of gas entrainment by numerical simulation with accurate physics model

Ito, Kei; Koizumi, Yasuo*; Ohshima, Hiroyuki; Kawamura, Takumi*

Proceedings of 2011 International Congress on Advances in Nuclear Power Plants (ICAPP '11) (CD-ROM), p.2085 - 2092, 2011/05

In the design study on a large-scale sodium-cooled fast reactor, the reactor vessel is compactified. However, such a reactor vessel induces higher coolant flows in the vessel and causes several thermal-hydraulics issues, e.g. gas entrainment (GE) phenomenon. To clarify the negative influences of the GE on the JSFR, not only the onset condition of the GE but also the entrained gas (bubble) flow rate has to be evaluated. In this study, the authors performs numerical simulations to investigate the entrained gas amount in a hollow vortex experiment. To simulate interfacial deformations accurately, a high-precision numerical simulation algorithm for gas-liquid two-phase flows is employed. As a result, the numerical simulation gives somewhat larger entrained gas flow rate than the experiment. However, both the numerical simulation and experiment show the entrained gas flow rates which are proportional to the outlet water velocity.

Journal Articles

Study on gas entrainment rate into liquid from free surface by vortex

Koizumi, Yasuo*; Ito, Kei; Ohshima, Hiroyuki; Otake, Hiroyasu*

Proceedings of 2010 ASME International Mechanical Engineering Congress & Exposition (IMECE 2010) (DVD-ROM), 6 Pages, 2010/11

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. The flow state of the entrainment was visually observed by using a high speed video camera. The gas entrainment rate into water was measured. A stable vortex was formed in the test vessel. Whether the bottom of the vortex reached the bottom outlet of the vessel was dependent on the velocity at the bottom outlet. Before the vortex tip reached the bottom of the vessel, bubbles were periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. After the bottom of the vortex reached the bottom of the vessel, the gas entrainment turned to the vortex-type gas entrainment. When the gas entrainment turned to the vortex-type gas entrainment, the flow state in the outlet pipe changed from the bubbly flow to the churn flow. After the gas entrainment varied from the bubble-type to the vortex-type, the gas entrainment rate increased drastically.

76 (Records 1-20 displayed on this page)