Refine your search:     
Report No.
 - 
Search Results: Records 1-20 displayed on this page of 98

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Development of regional downscaling capability in STEAMER ocean prediction system based on multi-nested ROMS model

Kamidaira, Yuki; Kawamura, Hideyuki; Kobayashi, Takuya; Uchiyama, Yusuke*

Journal of Nuclear Science and Technology, 56(8), p.752 - 763, 2019/08

Oceanic regional downscaling capability was implemented into Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) developed by Japan Atomic Energy Agency to enable us to predict more realistically the oceanic dispersion of radionuclides at higher spatiotemporal resolutions for broader applications. The system consisted of a double-nested oceanic downscaling circulation model with tidal forcing and an oceanic radionuclide dispersion model. This system was used to comparatively examine downscaling and tidal effects on the dispersion of radionuclides hypothetically released from the Fukushima Daiichi Nuclear Power Plant in the colder season. The simulated dissolved $$^{137}$$Cs distribution was different from that obtained using coarser-resolution models because downscaling enhanced both horizontal and vertical mixing. The suppression of horizontal mixing and the promotion of vertical mixing by tidal forcing synergistically reduced offshore $$^{137}$$Cs transport. In addition, the submesoscale effects strengthened the three-dimensional $$^{137}$$Cs fluctuations by $$<$$10 times, while the tidal effects promoted slightly increased the intensity of three-dimensional $$^{137}$$Cs fluctuations by approximately 3%. This indicated that the submesoscale effects substantially surpassed tidal forcing in oceanic mixing in the coastal margin off Fukushima in the colder season.

Journal Articles

Penetration of $$^{129}$$I released from Fukushima Daiichi Nuclear Power Plant accident in the western North Pacific Ocean

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

JAEA-Conf 2018-002, p.103 - 106, 2019/02

To investigate the dynamics of radionuclides in the ocean released by the accident at Fukushima Daiichi Nuclear Power Plant (1F), vertical distributions of $$^{129}$$ I at three stations in the western North Pacific was revealed. The 1F accident-derived $$^{129}$$ I existed within the mixed layer at 3 stations. The maximum layer of the 1F accident-derived $$^{129}$$ I existed at the depth of 370 m - 470 m at the most southern station. Considering the dissolved oxygen concentration and the current velocity arround the station, the maximum layer of the 1F accident-derived $$^{129}$$ I would be fromed that $$^{129}$$I which existed in the surface seawater at other area of observation point was carried to the depth of 370 m - 470 m by the fast downward flow.

Journal Articles

Vertical distribution of $$^{129}$$I released from the Fukushima Daiichi Nuclear Power Plant in the Kuroshio and Oyashio current areas

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

Marine Chemistry, 204, p.163 - 171, 2018/08

 Percentile:100(Chemistry, Multidisciplinary)

To investigate the penetration of radionuclides released from Fukushima Daiichi Nuclear Power Plant (FDNPP), depth profiles were revealed at Kuroshio current, transition, and Oyashio current areas. The FDNPP-derived $$^{129}$$I was found in surface layer at Oyashio current and transition areas and in sub-surface layer at Kuroshio current area. Moreover, it was found that the FDNPP-derived $$^{129}$$I/$$^{134}$$Cs ratios in the Oyashio current and transition areas were higher than that in the FDNPP reactor. The higher FDNPP-derived $$^{129}$$I/$$^{134}$$Cs ratios suggest three potential mechanisms for the migration of radionuclides in the environment: (1) radioiodine was released more easily than radiocesium by the FDNPP accident, (2) $$^{129}$$I was supplied from the atmosphere by re-emitted $$^{129}$$I from contaminated areas around Fukushima, (3) leaked water that removed radiocesium reached the sampling stations. The FDNPP-derived $$^{129}$$I in sub-surface layer would be transported by the meander of the Kuroshio Extension current.

Journal Articles

Submesoscale mixing on initial dilution of radionuclides released from the Fukushima Daiichi Nuclear Power Plant

Kamidaira, Yuki; Uchiyama, Yusuke*; Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko

Journal of Geophysical Research; Oceans (Internet), 123(4), p.2808 - 2828, 2018/04

We developed a submesoscale eddy-resolving oceanic dispersal modeling system consisting of a double nested oceanic downscaling model and an offline oceanic radionuclides dispersion model to investigate influences of submesoscale coherent structures (SCSs) and associated ageostrophic secondary circulations (ASCs) on the three-dimensional (3D) dispersal and initial dilution of the dissolved radioactive $$^{137}$$Cs accidentally released from the Fukushima Daiichi Nuclear Power Plant (FNPP1) occurred since March 2011. The extensive model-data comparison demonstrates that the elaborated innermost high-resolution model at a lateral grid resolution of 1 km successfully reproduces transient mesoscale oceanic structures, the Kuroshio path and stratification, and spatiotemporal variations of 3D $$^{137}$$Cs concentrations. These SCSs and ASCs occurred primarily due to shear instability with baroclinic instability as the secondary mechanism, according to energy conversion and spectral analyses. The vertical $$^{137}$$Cs flux analysis was performed with decomposition of the variables into the mean, mesoscale, and submesoscale components using frequency and wavenumber filters. The vertical $$^{137}$$Cs flux analysis explained that 84% of the FNPP1-derived $$^{137}$$Cs was transported downward below the mixed layer by eddies, with the major contributions from ASCs induced by submesoscale eddies.

Journal Articles

Oceanic dispersion of Fukushima-derived Cs-137 simulated by multiple oceanic general circulation models

Kawamura, Hideyuki; Furuno, Akiko; Kobayashi, Takuya; In, Teiji*; Nakayama, Tomoharu*; Ishikawa, Yoichi*; Miyazawa, Yasumasa*; Usui, Norihisa*

Journal of Environmental Radioactivity, 180, p.36 - 58, 2017/12

 Times Cited Count:2 Percentile:69.03(Environmental Sciences)

This study simulates the oceanic dispersion of Fukushima-derived Cs-137 by an oceanic dispersion model and multiple oceanic general circulation models. The models relatively well reproduced the observed Cs-137 concentrations in the coastal, offshore, and open oceans. Multiple simulations in the coastal, offshore, and open oceans consistently suggested that Cs-137 dispersed along the coast in the north-south direction during the first few months post-disaster, and were subsequently dispersed offshore by the Kuroshio Current and Kuroshio Extension. Quantification of the Cs-137 amounts suggested that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layers in the North Pacific.

Journal Articles

Development of a short-term emergency assessment system of the marine environmental radioactivity around Japan

Kobayashi, Takuya; Kawamura, Hideyuki; Fujii, Katsuji*; Kamidaira, Yuki

Journal of Nuclear Science and Technology, 54(5), p.609 - 616, 2017/05

 Times Cited Count:2 Percentile:42.02(Nuclear Science & Technology)

The Japan Atomic Energy Agency has, for many years, been developing a radionuclide dispersion model for the ocean, and has validated the model through application in many sea areas using oceanic flow fields calculated by the ocean model. The Fukushima Dai-ichi Nuclear Power Station accident caused marine pollution by artificial radioactive materials to the North Pacific, especially to coastal waters northeast of mainland Japan. In order to investigate the migration of radionuclides in the ocean caused by this severe accident, studies using marine dispersion simulations have been carried out by JAEA. Based on these as well as the previous studies, JAEA has developed the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) to immediately predict the radionuclide concentration around Japan in case of a nuclear accident.

Journal Articles

Development of a prediction system for radionuclide dispersion in Fukushima coast

Kamidaira, Yuki; Kawamura, Hideyuki; Kobayashi, Takuya; Uchiyama, Yusuke*

Doboku Gakkai Rombunshu, B2 (Kaigan Kogaku) (Internet), 72(2), p.I_451 - I_456, 2016/11

no abstracts in English

Journal Articles

Numerical simulation on the long-term variation of radioactive cesium concentration in the North Pacific due to the Fukushima disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*

Journal of Environmental Radioactivity, 136, p.64 - 75, 2014/10

 Times Cited Count:15 Percentile:33.84(Environmental Sciences)

Numerical simulations on oceanic radioactive cesium dispersions in the North Pacific were conducted with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster. It was suggested that the $$^{137}$$Cs concentration had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.

Journal Articles

Drift simulation of tsunami debris in the North Pacific

Kawamura, Hideyuki; Kobayashi, Takuya; Nishikawa, Shiro*; Ishikawa, Yoichi*; Usui, Norihisa*; Kamachi, Masafumi*; Aso, Noriko*; Tanaka, Yusuke*; Awaji, Toshiyuki*

Global Environmental Research (Internet), 18(1), p.81 - 96, 2014/09

A drift simulation of tsunami debris flushed out from the Tohoku district, Japan, into the North Pacific due to the tsunami on March 11, 2011, has been conducted to monitor and forecast the drift path over the North Pacific. Results showed that tsunami debris was first transported eastward by the intense Kuroshio Extension and westerly, spreading in the north and south directions by both an energetic ocean eddy and a storm track over the ocean. Tsunami debris with larger windage was transported over the North Pacific by ocean surface wind rather than ocean current and arrived at the west coast of the North American Continent in the fall of 2011. Tsunami debris located near the North American Continent migrated, associated with the basin-scale seasonal change in the atmospheric pressure pattern. Our forecast run suggested that the tsunami debris belt will be formed from the North American Continent in the east to the Philippines in the west.

Journal Articles

Intercomparison of numerical simulations on oceanic dispersion of the radioactive cesium released because of the Fukushima disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*; Nishikawa, Shiro*; Ishikawa, Yoichi*

Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 7 Pages, 2014/08

Numerical simulations on oceanic dispersion of the radioactive cesium in the North Pacific from March 2011 to September 2013 were conducted to clarify the concentration of the radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant. We implemented the oceanic dispersion simulations with two independent ocean reanalysis dataset. It was suggested that the $$^{137}$$Cs concentration in the North Pacific was lower than the pre-Fukushima background level about two years after the Fukushima disaster. The intercomparison revealed that meso-scale eddies in the Kuroshio Extension region may have efficiently diluted the radioactive cesium concentration at the sea surface. In addition, it was suggested that the enhanced downward current accompanied by the meso-scale eddies played an important role in transporting the radioactive cesium into the intermediate layer.

Journal Articles

Iodine-129 concentration in seawater near Fukushima before and after the accident at the Fukushima Daiichi Nuclear Power Plant

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

Biogeosciences, 10(6), p.3839 - 3847, 2013/06

 Times Cited Count:14 Percentile:37.85(Ecology)

no abstracts in English

Journal Articles

Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations

Kobayashi, Takuya; Nagai, Haruyasu; Chino, Masamichi; Kawamura, Hideyuki

Journal of Nuclear Science and Technology, 50(3), p.255 - 264, 2013/03

AA2012-0777.pdf:1.24MB

 Times Cited Count:94 Percentile:0.17(Nuclear Science & Technology)

The source term of the atmospheric release of $$^{131}$$I and $$^{137}$$Cs due to the Fukushima Dai-ichi Nuclear Power Plant accident estimated by previous studies was validated and refined by coupling atmospheric and oceanic dispersion simulations with observed $$^{134}$$Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for $$^{134}$$Cs and $$^{137}$$Cs, the sea surface concentration of $$^{134}$$Cs was calculated using the previously estimated source term and was compared with measurement data. The release rate of $$^{137}$$Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of $$^{131}$$I was refined to follow the radioactivity ratio of $$^{137}$$Cs. As a result, the total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.0$$times$$10$$^{17}$$ and 1.3$$times$$10$$^{16}$$ Bq, respectively.

Journal Articles

Numerical experiments on dispersion of radionuclides in the ocean released from the Fukushima Daiichi Nuclear Power Plant

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; In, Teiji*; Ishikawa, Yoichi*; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*

Reports of Research Institute for Applied Mechanics, Kyushu University, (143), p.111 - 117, 2012/09

Because of the Fukushima Dai-ichi Nuclear Power Plant disaster, some radionuclides were released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant. In response to this situation, numerical experiments were carried out at Japan Atomic Energy Agency using an oceanic dispersion model and an ocean general circulation model to estimate an effect of the radionuclides on marine environment. It was suggested that the radionuclides deposited from the atmosphere mainly in the middle of March after the disaster spread over a comparatively wide area of the Pacific Ocean east of Japan. On the other hand the radionuclides directly released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant were carried along the coast and then spread along the Kuroshio extension.

Journal Articles

Influencec of atmospheric disturbances on the lower trophic level ecosystem in the Japan Sea

Onitsuka, Go*; Yanagi, Tetsuo*; Uno, Itsushi*; Kawamura, Hideyuki; Yoon, J.-H.*; Yamanaka, Yasuhiro*

Engan Kaiyo Kenkyu, 50(1), p.45 - 51, 2012/08

A seasonal variation of phytoplankton concentration is remarkable in the surface layer of the Japan Sea, because of a seasonal variation of solar radiation and nutrient. While, it is suggested that atmospheric perturbation such as typhoon effects a lower level ecosystem in the surface layer. An effect of atmospheric perturbation on the lower level ecosystem was estimated by means of an ocean general circulation model and a lower level ecosystem model in this study. Results of numerical experiments suggested that the atmospheric perturbation enhances a primary production in the Japan Sea.

Journal Articles

Oceanic dispersion simulations of $$^{137}$$Cs released from the Fukushima Daiichi Nuclear Power Plant

Masumoto, Yukio*; Miyazawa, Yasumasa*; Tsumune, Daisuke*; Tsubono, Takaki*; Kobayashi, Takuya; Kawamura, Hideyuki; Estournel, C.*; Marsaleix, P.*; Lanerolle, L.*; Mehra, A.*; et al.

Elements, 8(3), p.207 - 212, 2012/06

 Times Cited Count:60 Percentile:3.77(Geochemistry & Geophysics)

Present status of oceanic dispersion simulations of cesium 137 ($$^{137}$$Cs) directly discharged from Fukushima Daiichi Nuclear Power Plant are reviewed using five model outputs and other available informations, focusing on estimations of discharged amount of $$^{137}$$Cs and subsequent dispersion in a region off Fukushima during March and April, 2011. Common aspects and discrepancies among the simulated results are described. While the discharged amount spreads from about 1 to 27 P Bq of $$^{137}$$Cs among the estimates, the values obtained from the five models indicate 2 to 4 P Bq. With these total amounts and time evolutions of the discharge rate, mimicking observed $$^{137}$$Cs concentration near FDNPP, as a source for the dispersion calculation, all the five models simulated the $$^{137}$$Cs dispersion in the ocean reasonably well corresponding to the observed distributions.

Journal Articles

Preliminary numerical experiments on Oceanic dispersion of $$^{131}$$I and $$^{137}$$Cs discharged into the ocean because of the Fukushima Daiichi Nuclear Power Plant disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; In, Teiji*; Ishikawa, Yoichi*; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*

Journal of Nuclear Science and Technology, 48(11), p.1349 - 1356, 2011/11

AA2011-0314.pdf:0.68MB

Numerical experiments were carried out to predict the spreading of $$^{131}$$I and $$^{137}$$Cs released into the ocean due to the Fukushima Daiichi Nuclear Power Plant incident. Results in the numerical experiments were in good agreement with the concentrations of $$^{131}$$I and $$^{137}$$Cs in the monitoring data. It was suggested that the high $$^{131}$$I concentration detected in the young lancefish caught off Kitaibaraki city was due to the deposition from the atmosphere. The numerical experiments suggest that the deposition of radionuclides released into the atmosphere in the middle March largely effected the concentrations of radionuclides east of Japan in the Pacific Ocean.

Journal Articles

A Study of released radionuclide in the coastal area from a discharge pipe of nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan

Kobayashi, Takuya; In, Teiji*; Ishikawa, Yoichi*; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Awaji, Toshiyuki*; Togawa, Orihiko

Progress in Nuclear Science and Technology (Internet), 2, p.682 - 687, 2011/10

When the reprocessing plant is in routine operation, radionuclides are released to the coastal ocean as scheduled. Released radionuclides migrate in the ocean by physical, chemical and biological processes. Thus, for environmental safety, it is important to understand the migration behavior due to routine releases of radionuclides to the coastal ocean from the reprocessing plant. A numerical simulation model system that consists of an ocean general circulation model and a particle random-walk model to describe the radionuclide migration behavior in Rokkasho coastal region has been developed. The particle random-walk model, SEA-GEARN, calculates the radionuclides migration in the ocean. The system has been applied to simulate the nowcast of Rokkasho coastal region in 2007 and hypothetical radionuclide release has been carried out.

Journal Articles

Assessment system of marine environment in the Japan Sea

Kawamura, Hideyuki; Kobayashi, Takuya; Togawa, Orihiko; Onitsuka, Go*

Proceedings of 7th International Conference on Natural Computation (ICNC '11)/8th International Conference on Fuzzy Systems and Knowledge Discovery (FSKD '11), p.1742 - 1746, 2011/07

An assessment system of marine environment in the Japan Sea is developed in Japan Atomic Energy Agency to calculate a movement of pollutants such as radionuclides and their effect on Japanese people. The assessment system consists of three models, ocean general circulation model, particle random-walk model, and dose assessment model. The assessment system was applied so far to a numerical experiment of an oil spill accident and a numerical experiment for reproduction of concentration of anthropogenic radionuclides in the Japan Sea. In addition, the lower trophic level ecosystem model is being developed to estimate a suspended solid in the Japan Sea.

Journal Articles

Numerical experiment for strontium-90 and cesium-137 in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*; Togawa, Orihiko

Journal of Oceanography, 66(5), p.649 - 662, 2010/10

 Times Cited Count:2 Percentile:90.64(Oceanography)

A numerical experiment is performed to reproduce a distribution of concentrations of $$^{90}$$Sr and $$^{137}$$Cs and estimate their total amounts in the Japan Sea. The concentrations of $$^{90}$$Sr and $$^{137}$$Cs in the surface layer is in the range of 1.0-1.5 Bq/m$$^{3}$$ and 2.0-2.5 Bq/m$$^{3}$$. The concentrations in the intermediate and deep layer are higher than those observed in the northwestern Pacific Ocean, indicating active winter convection in the Japan Sea. The total amounts of $$^{90}$$Sr and $$^{137}$$Cs in the seawater is evaluated to be 1.34 PBq (1 PBq = 10$$^{15}$$ Bq) and 2.02 PBq, which demonstrates an estimation by observational data in the Japan Sea expeditions between 1997 and 2002 by Japan Atomic Energy Agency. The total amounts of $$^{90}$$Sr and $$^{137}$$Cs vary corresponding to deposition at the sea surface with the maximums of 4.86 PBq for $$^{90}$$Sr and 7.33 PBq for $$^{137}$$Cs in the mid-1960s.

Journal Articles

Simulation of concentrations of anthropogenic radionuclides in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*; Togawa, Orihiko

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 4 Pages, 2010/10

This study aims to demonstrate many findings in the Japan Sea expeditions by Japan Atomic Energy Agency between 1997 and 2002 making use of an ocean general circulation model. A numerical experiment is performed between 1945 and 2000 with deposition at the sea surface by global fallout as main source of anthropogenic radionuclides. The concentrations of $$^{90}$$Sr and $$^{137}$$Cs in the surface layer are approximately in the range of 1.0-1.5 Bq/m$$^{3}$$ and 2.0-2.5 Bq/m$$^{3}$$ and they exponentially decrease with depth from the sea surface to the sea bottom. Total amounts of $$^{90}$$Sr and $$^{137}$$Cs in the seawater of the Japan Sea are estimated to be about 1.34 PBq (1 PBq = 10$$^{15}$$ Bq) and 2.02 PBq in the numerical experiment, which demonstrates observational estimations in the Japan Sea expeditions. Time series of the total amounts show that they attain the maximums of 4.86 PBq for $$^{90}$$Sr and 7.33 PBq for $$^{137}$$Cs in 1964.

98 (Records 1-20 displayed on this page)