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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:9 Percentile:44.19(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 ocean dispersion concentration maps of the contaminated water released from the Fukushima Dai-ichi Nuclear Power Plant

Kobayashi, Takuya; In, Teiji*; Ishikawa, Yoichi*

Journal of Nuclear Science and Technology, 52(6), p.769 - 772, 2015/06

 Times Cited Count:1 Percentile:12.03(Nuclear Science & Technology)

Ocean diffusion concentration maps were developed to gain an understanding of the migration behavior of contaminated water leaking from the Fukushima Dai-ichi Nuclear Power Plant. We used ensemble mean values to define the semi-climatological seasonal field in our calculations of the trajectories of the contaminated water. The maps were validated by conducting actual release events in two different seasons. The results showed that despite their simplicity, the proposed methods yield relatively good results.

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

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

 Times Cited Count:155 Percentile:99.81(Nuclear Science & Technology)

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.

JAEA Reports

Improvement of the marine radionuclides prediction code in the off Shimokita Region

Kobayashi, Takuya; Togawa, Orihiko; Ito, Toshimichi; Otosaka, Shigeyoshi; Kawamura, Hideyuki; Hayashi, Keisuke*; Shima, Shigeki*; Nakayama, Tomoharu*; In, Teiji*

JAEA-Research 2009-040, 63 Pages, 2009/12

JAEA-Research-2009-040.pdf:12.19MB

A spent nuclear fuel reprocessing plant has the possibility of routine releases of liquid radioactive wastes from a discharge pipe to the off Shimokita region during its operations. Thus, for environmental safety, it is important to assess the migration processes of released radionuclides from the plant. Therefore, an ocean circulation prediction code and an oceanic radionuclides migration prediction code, which were developed by Japan Atomic Energy Agency, has been improved to describe the migration behavior of radionuclides in the off Shimokita region. Parameters on characteristics and dynamics of particulate materials in seawater have also been obtained in the study area for the adjustment and verification of the oceanic radionuclides migration prediction code. This report summarizes the primary results of the study which was carried out at the off Shimokita region from FY2003 to 2008.

Journal Articles

Development of a system for the prediction of radionuclide migration in the off Shimokita region and its case study

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

Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(2), p.112 - 126, 2008/06

The radionuclides migration forecasting system in the off Shimokita region has been developed to predict the routine and accidental releases of liquid radioactive wastes during the operations of a spent nuclear fuel reprocessing plant in Aomori prefecture, Japan. The results obtained from the case studies are as follows; (1) The ocean general circulation model by using the techniques of data assimilation and nesting reproduced well the flow pattern of a coastal area. (2) The estimated internal dose due to ingestion of marine products from hypothetical release of $$^{3}$$H was 0.45 $$mu$$Sv/y. (3) The results of hypothetical release of $$^{137}$$Cs showed that about four percent of the whole deposited on the seabed after a 60-day calculation. The concentration of $$^{137}$$Cs of hypothetical release from the off Shimokita region is the same or less than that of global fallout measured at the same area.

Journal Articles

The Oceanic forecasting system near the Shimokita Peninsula, Japan

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

Proceedings of International Symposium on Environmental Modeling and Radioecology, p.58 - 64, 2007/03

The northwestern part of the Pacific Ocean off the Shimokita Peninsula assumes a complex water mass structure. It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model. We have planned to make use of a one-way nesting method. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. The assimilated data consist of hydrographic observations collected through the Global Temperature-Salinity Profile Program, sea surface temperature and sea surface height data observed by satellites. A forecast experiment on the basis of oceanographic observations made in 2003 illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.

Journal Articles

Development of the ocean forecasting system for Shimokita region

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

Gekkan Kaiyo, 37(9), p.674 - 680, 2005/09

no abstracts in English

Oral presentation

Preliminary calculation of influences on the North Pacific by the nuclear testing around the Bikini Atoll using SEA-GEARN

Matsuura, Yasutaka*; Nakayama, Tomoharu*; In, Teiji*; Gasa, Shinichi*; Shima, Shigeki*; Kobayashi, Takuya; Togawa, Orihiko; Ishikawa, Yoichi*; Awaji, Toshiyuki*

no journal, , 

no abstracts in English

Oral presentation

Development of hindcast and forecast ocean system off Rokkasho, 3; Data assimilation system in northwestern Pacific ocean

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

no journal, , 

no abstracts in English

Oral presentation

Development of hindcast and forecast ocean system off Rokkasho, 4; Hindcast experiment on 2003

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

no journal, , 

no abstracts in English

Oral presentation

The Oceanic forecasting system near the Shimokita Peninsula, Japan

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

no journal, , 

The Shimokita Peninsula (hereafter SP)is located at the northeast tip of Honshu (the main island of Japan) and borders on the northwestern part of the North Pacific Ocean (hereafter NWNP) in the east and the Tsugaru Strait (hereafter TS) in the north. It is known that the NWNP off the SP assumes a complex water mass structure. Seawater of Japan Sea origin, called the Tsugaru Warm Water (TWW) component, takes on a characteristic seasonal variation. Conlon (1982) pointed out that during winter and spring, the TWW in the NWNP propagates southward along the coast of the peninsula (the coastal mode), and swirls off the peninsula from summer to autumn (the gyre mode). It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model (OGCM). We need to use a fine-scale grid, probably such as 1-2 km in size to reproduce the water mass structure around the TS and the off the SP in detail. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. A forecast experiment on the basis of oceanographic observations made in 2003 (a hindcast experiment) illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.

Oral presentation

Nowcasting/forecasting system of the ocean circulation off Rokkasho village

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

no journal, , 

We have been developing an oceanic forecasting/nowcasting system for the coastal area near Rokkasho village, which locates in the northern part of Honshu Island of Japan. Associated with the geographic features, the oceanographic condition in this area is very complicated. Previous observations show that the seasonal variation in this region is characterized by the two different modes: the coastal mode in a cold season in which flow takes a straight path along the Japan coast, and the gyre mode in a warm season in which swirl-like circulation appears. When attempting the accurate nowcast/forecast of this complicated regional circulation, a downscaling method is an effective approach since it enables us to use such a high resolution 4-dimensional variational data assimilation system. In fact, our forecast result using the high resolution data assimilation system demonstrates the good performance of reproducing both modes in a hindcast sense.

Oral presentation

The Simulation on seasonal variation of the Tsugaru Warm Current by the ocean forecasting system off Rokkasho village

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

no journal, , 

An oceanic forecasting system for coastal area near Rokkasho village has been developed. A circulation in this area is primarily controlled by the seasonally-varying Tsugaru Warm Current and the Oyashio. Previous observations suggest that seasonal variation in this region is characterized by two different modes: the coastal mode in cold seasons and the gyre mode in warm seasons. To attempt the accurate forecast, a downscaling method is an effective approach because it enables us to use a high resolution 4-dimensional variational data assimilation system. Model results realistically reproduced the seasonal variation of the Tsugaru Warm Current and the Oyashio from May in 2003 to January in 2004.

Oral presentation

Nowcasting/forecasting system of the ocean circulation off Rokkasho Village

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

no journal, , 

We have been developing an oceanic nowcasting/forecasting system for the coastal area near Rokkasho village. The seasonal variation in this region is characterized by the coastal mode in a cold season and the gyre mode in a warm season. A downscaling method is an effective approach for the accurate nowcast/forecast, since it enables us to use a high resolution 4-dimensional variational data assimilation. Our results demonstrate the good performance of reproducing both modes.

Oral presentation

Development process of the Tsugaru gyre

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

no journal, , 

A clockwise circulation called the Tsugaru gyre is formed from summer to autumn after the Tsugaru Warm Current passes through the Tsugaru Strait into the Pacific Ocean. This study aims to clarify a formation process of the Tsugaru gyre by a numerical model and observational data. It is suggested that a separation of the Tsugaru gyre from the coast is related to a strong southward current near the coast resulted from a penetration of the Oyashio to the Tsugaru Warm Current.

Oral presentation

A Study on the discharge of effluent at the near field of nuclear fuel reprocessing plant by an oceanic radionuclides migration forecast model of SPEEDI-MP

Kobayashi, Takuya; Kawamura, Hideyuki; In, Teiji*; Shima, Shigeki*

no journal, , 

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 the off Rokkasho-mura, Aomori-ken, Japan has been developed. The system has been applied to simulate the nowcast of Rokkasho coastal region in 2007 and hypothetical radionuclide release has been carried out.

Oral presentation

Radionuclides migration forecast in the off Fukushima region

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

no journal, , 

The radionuclides migration forecasting system in the off Fukushima region and near Japan region has been developed to predict the accidental releases of liquid radioactive materials from the Fukushima Dai-ichi Nuclear Poower Plant in Japan.

Oral presentation

Intercomparison of oceanic dispersion simulations on the Fukushima-derived $$^{137}$$Cs

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

no journal, , 

Oceanic dispersion simulations include errors originated from source terms, oceanographic data, etc. In this study, the oceanic dispersion simulations were carried out with five oceanographic data in order to analyze an effect of oceanographic data on $$^{137}$$Cs dispersion and clarify $$^{137}$$Cs dispersion in the coastal area and the open ocean. The high-resolution simulation could well reproduce the observed $$^{137}$$Cs concentration in Fukushima Prefecture and it suggested that directly-released $$^{137}$$Cs into the ocean dispersed in the north-south direction during a few months after the Fukushima disaster. The relatively low-resolution simulations could reproduce main currents in the North Pacific and they suggested that the Kuroshio Extension played an important role on $$^{137}$$Cs transport from the coastal area to the open ocean. Moreover, it was demonstrated that $$^{137}$$Cs was transported from the mixed layer to the deeper layer 1 year after the Fukushima disaster.

Oral presentation

Oceanic dispersion of Fukushima-derived Cs-137 in the coastal, offshore, and open oceans simulated by multiple oceanic general circulation models

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

no journal, , 

This study simulates the oceanic dispersion of Fukushima-derived Cs-137 by an oceanic dispersion model SEA-GEARN-FDM and multiple oceanic general circulation models. The oceanic dispersion simulations relatively well reproduced the measured Cs-137 concentrations in the coastal and offshore oceans during the first few months after the Fukushima disaster, and in the open ocean during the first year post-disaster. It was 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. The Cs-137 amounts were quantified in the coastal, offshore, and open oceans during the first year post-disaster. It was demonstrated that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layer in the North Pacific.

21 (Records 1-20 displayed on this page)