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JAEA Reports

Ocean current data obtained by Acoustic Doppler Current Profiler across the Tsugaru Strait (Joint research)

Kawamura, Hideyuki; Hirose, Naoki*; Nakayama, Tomoharu*; Ito, Toshimichi

JAEA-Data/Code 2021-004, 34 Pages, 2021/05

JAEA-Data-Code-2021-004.pdf:3.72MB

The Japan Atomic Energy Agency measured the ocean current across the Tsugaru Strait using an Acoustic Doppler Current Profiler attached on a ferryboat from October 1999 to January 2008. The characteristics of the ocean current in the Tsugaru Strait must be understood for predicting oceanic dispersion of radioactive materials released from nuclear facilities around the strait. Furthermore, it is critical to elucidate the mechanism of the Tsugaru Warm Current from an oceanography viewpoint. The dataset obtained in this investigation consists of daily ocean current data files that record the components of the current speed in the east-west and north-south directions from the surface layer to the bottom layer. The dataset stores 2,211 daily ocean current data files, despite some data periods missing from October 1999 to January 2008. In this study, information on the dataset is described for users to analyze the dataset properly for their purposes. Section 1 provides the background and purpose of the ocean current measurement, Section 2 explains the methodology of measurement using an Acoustic Doppler Current Profiler, and Section 3 explains the record format of the daily ocean current data files and data acquisition rate and presents analysis results. Finally, Section 4 concludes this study.

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:7.46(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.

JAEA Reports

Establishment of database for Japan Sea parameters on marine environment and radioactivity (JASPER), 2; Radiocarbon and oceanographic properties

Otosaka, Shigeyoshi; Suzuki, Takashi; Tanaka, Takayuki; Ito, Toshimichi; Kobayashi, Takuya; Kawamura, Hideyuki; Minakawa, Masayuki*; Aramaki, Takafumi*; Senju, Tomoharu*; Togawa, Orihiko

JAEA-Data/Code 2009-020, 27 Pages, 2010/02

JAEA-Data-Code-2009-020.pdf:2.45MB

The database for the Japan Sea parameters on marine environment and radionuclides (JASPER) has been established by the Japan Atomic Energy Agency as a product of the Japan Sea Expeditions. By the previous version of the database, data for representative anthropogenic radionuclides were opened to public. And now, data for radiocarbon and fundamental oceanographic properties (salinity, temperature, dissolved oxygen) including nutrients (silicate, phosphate, nitrate and nitrite) are released as the second volume of the database. In the second volume, 20,398 data records are stored including 2,695 data for temperature, 2,883 data for salinity, 2,109 data for dissolved oxygen, 11,051 data for the nutrients, and 1,660 data for radiocarbon. The database will be a strong tool for the continuous monitoring for contamination by anthropogenic radionuclides, studies on biogeochemical cycle, and development and validation of models for numerical simulations in the sea.

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

Modeling of the branches of the Tsushima Warm Current in the eastern Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Hirose, Naoki*; Takikawa, Tetsutaro*; Yoon, J.-H.*

Journal of Oceanography, 65(4), p.439 - 454, 2009/08

 Times Cited Count:4 Percentile:14.2(Oceanography)

This study aims at reproducing branches of the Tsushima Warm Current making use of an ocean general circulation model, which is important for movement of pollutants in the Japan Sea. The model was laterally exerted by volume transports measured by ADCP through the Tsushima Straits and the Tsugaru Strait. Sea level variation measured by coastal tide-stations as well as satellite altimeters is assimilated into the numerical model. It was demonstrated that an assimilation of sea level variation at the coastal tide-stations is useful to simulate oceanic condition in the nearshore region.

Journal Articles

Investigation using accoustic signal; Sound-scene in the Tsugaru Strait

Onishi, Mitsuyo*; Ito, Toshimichi

Rikatan (Rika No Tanken), 3(6), p.26 - 27, 2009/06

This document is written for primary and secondary school student to explain the measurement of ocean flow using acoustic signal. In this document, principle and ferry mounted method of Acoustic Doppler Current Profiler (ADCP) measurement are introduced, and a part of results obtained through the measurement in the Tsugaru Strait is shown. Additionally, the importance of the measurement in the study of the Japan Sea is mentioned shortly. The measurement was carried out under the cooperative research between JAEA and Japan Marine Science Foundation getting a voluntary help from Higashi-Nihon Ferry Co. Ltd..

Journal Articles

Variation of volume transport of the Tsugaru Warm Current in the period from 2000 to 2002

Ito, Toshimichi; Kawamura, Hideyuki; Nakayama, Tomoharu*; Shima, Shigeki*; Onishi, Mitsuyo*; Isoda, Yutaka*

Proceedings of International Workshop on Monitoring and Forecasting of the Rapid Change in Ocean-Atmosphere Environment in the East Asia, p.13 - 14, 2007/11

The volume transport of the Tsugaru Warm Current (TgWC) from April 2000 to June 2002, which was estimated based on the ferry-borne ADCP observation was examined in this study. The estimated transport varied from about 0.6 Sv to 2.5 Sv (=10$$^{6}$$ m$$^{3}$$s$$^{-1}$$), and the mean value was estimated to be about 1.3 Sv with $$pm$$ 0.3 Sv showing the similar level as that in the preliminary result. The temporal variation with a period of about 20-30 days seemed to be remarkable in the anterior half of this observation period rather than seasonal variation. By contrast, the seasonal variation was dominant in the posterior half in which the minimum and maximum values appear in the spring and autumn, respectively. The temporal change of the transport showed good correlation with the sea level differences around the strait as expected. In addition, the present result suggests that the change of local wind around the strait also lead in part of the change of the transport.

Journal Articles

Transport processes of radionuclides in the Japan Sea obtained by JAEA's expeditions

Togawa, Orihiko; Ito, Toshimichi; Otosaka, Shigeyoshi

Hoken Butsuri, 42(3), p.234 - 246, 2007/09

The Japan Atomic Energy Agency (JAEA) has carried out expeditions in the Japanese and Russian exclusive economic zones (EEZ) of the Japan Sea for 10 years to clarify seawater circulation and transport processes of radionuclides in the sea. The Japan Sea expeditions by JAEA started with its participation in the Japanese-Korean-Russian joint expeditions of 1994 and 1995. Through 18 expeditions, JAEA succeeded in covering almost all areas of the Japan Sea that can be observed at present. As a result, for the first time, JAEA has made distribution maps of anthropogenic radionuclides in the Japan Sea and outlined the transport processes of radionuclides in the sea. Furthermore, we also obtained the results on water circulation and oceanographic features of the Japan Sea. This review summarizes representative and important results obtained in the Japan Sea expeditions by JAEA. The dataset on the distribution of anthropogenic radionuclides established by this study provides background data in assessing the radiological consequences in cases of radioactive waste disposal in the sea or nuclear emergency response to accidental releases of radionuclides in or near the Japan Sea.

Journal Articles

Estimation of total amounts of anthropogenic radionuclides in the Japan Sea

Ito, Toshimichi; Otosaka, Shigeyoshi; Kawamura, Hideyuki

Journal of Nuclear Science and Technology, 44(6), p.912 - 922, 2007/06

 Times Cited Count:10 Percentile:60.87(Nuclear Science & Technology)

The total amount of anthropogenic radionuclides - $$^{90}$$Sr, $$^{137}$$Cs and $$^{239+240}$$Pu - in the Japan Sea were estimated for the first time. Inventories of seawater, seabed sediment and total at each sampling site varied depending on the water depth of the sites, and the total inventories for $$^{90}$$Sr, $$^{137}$$Cs and $$^{239+240}$$Pu were in the range of 0.52-2.8 kBqm$$^{-2}$$, 0.64-4.1 kBqm$$^{-2}$$ and 27-122 Bqm$$^{-2}$$, respectively. Using the dependency of the seawater and seabed sediment and gridded water depth data, the total amounts in the Japan Sea were estimated to be about 1.2$$pm$$0.4 PBq for $$^{90}$$Sr, 1.8$$pm$$0.7 PBq for $$^{137}$$Cs and 69$$pm$$14 TBq for $$^{239+240}$$Pu, and their total was about 3.1 PBq. The amount ratio of these radionuclides ($$^{90}$$Sr : $$^{137}$$Cs : $$^{239+240}$$Pu) became to be 1.0 : 1.6 : 0.059 implying selective accumulation of the plutonium isotopes. This implication was supported by the balance between the existing and supplied amounts, in which the existing $$^{90}$$Sr and $$^{137}$$Cs were comparable for the supplied while the existing $$^{239+240}$$Pu exceeded the supplied in nearly 40 %. This work were performed using the observation data obtained through a wide-area research project, "Japan Sea Expeditions", carried out during 1997-2003 and covered the Japanese and Russian exclusive economic zones.

Journal Articles

Variation of volume transport of the Tsugaru Warm Current in the period from 2000 to 2002

Ito, Toshimichi; Kawamura, Hideyuki; Onishi, Mitsuyo*; Isoda, Yutaka*; Nakayama, Tomoharu*; Shima, Shigeki*

Proceedings of 14th PAMS/JECSS Workshop, p.222 - 223, 2007/05

no abstracts in English

Journal Articles

Formation rate of water masses in the Japan Sea

Kawamura, Hideyuki; Yoon, J.-H.*; Ito, Toshimichi

Journal of Oceanography, 63(2), p.243 - 253, 2007/04

 Times Cited Count:9 Percentile:21.94(Oceanography)

Water masses in the subsurface and intermediate layer are formed vigorously due to strong winter convection in the Japan Sea. Taking it into account that a part of pollutants is carried into the layer below the sea surface together with such water masses, it is significant to estimate a formation rate and turnover time of water masses to study a fate of pollutants. This study aims to estimate the formation rate and turnover time of water masses by using a three-dimensional ocean circulation model and particle chasing method. The total formation rate of water masses below the sea surface amounts to about 3.63 Sv in the Japan Sea. The formation rates of the Upper portion of the Japan Sea Proper Water (UJSPW) and Japan/East Sea Intermediate Water (JESIW) are estimated to be about 0.37 and 1.51 Sv, respectively. An estimate of turnover time shows that the UJSPW and JESIW circulate in the subsurface and intermediate layer with time scales of about 22.6 and 2.1 years, respectively.

JAEA Reports

Establishment of a database for Japan Sea parameters on marine environment and radioactivity (JASPER), 1; Anthropogenic radionuclides (Contract research)

Ito, Toshimichi; Otosaka, Shigeyoshi; Suzuki, Takashi; Tanaka, Takayuki; Tsuneyama, Teppei; Togawa, Orihiko

JAEA-Data/Code 2007-008, 41 Pages, 2007/03

JAEA-Data-Code-2007-008.pdf:3.11MB

The database for the Japan Sea parameters on marine environment and radionuclides (JASPER) is established by the Japan Atomic Energy Agency as one of the final products of the Japan Sea Expeditions (phase I) carried out covering the EEZs of Japan and Russian Federation. And now, the part for anthropogenic radionuclides in the JASPER database is opened to the public, prior to the release of succeeding parts including other radionuclides, chemical tracers and oceanographic parameters. In the present, 253 data records are stored in the database including 193 data for $$^{90}$$Sr and $$^{137}$$Cs, 163 data for $$^{238}$$Pu and 236 data for $$^{239+240}$$Pu obtained from seawater, seabed sediment and filtered particle with support data. By establishing the database, recent feature of the Japan Sea environment has been recorded using every possible parameter for us. We believe that this database might be a strong tool for the purposes of monitoring for contamination of the Japan Sea by anthropogenic radionuclides, study of material transport in the sea and development and validation of models for numerical simulations. Furthermore, it is being prepared that the database are linked to MARIS of IAEA-MEL in order to contribute the world-wide study and monitoring of anthropogenic radionuclides in marine environment.

Journal Articles

Balance of anthropogenic radionuclides in the Japan Sea

Tsuneyama, Teppei; Ito, Toshimichi; Otosaka, Shigeyoshi

Proceedings of International Symposium on Environmental Modeling and Radioecology, p.236 - 239, 2007/03

The purpose of this study is to investigate the balance of the radionuclides in the Japan Sea by examining the all available data. In order to investigate the balance of the radionuclides in the Japan Sea, we examine the temporal changes of existing, incoming and outgoing amounts. The incoming amount is estimated as the sum of the amounts supplied from the atmosphere by global fallout and from the East China Sea by the Tsushima Warm Current. The outgoing amount is estimated as the sum of the amounts discharged from the Japan Sea and to seabed sediment. The existing amount is estimated by integrating the inventories over a whole surface of the Japan Sea. So, the temporal change of inventories must be elucidated in examining the temporal change of the existing amount. From the result, it is suggested that the rapid vertical transport exists in the Japan Sea as well as the slow transport. In our presentation, the balance of the radionuclides in seawater of the Japan Sea will be elucidated.

Journal Articles

Study on migration behavior of anthropogenic radionuclides in the Japan Sea, 4

Otosaka, Shigeyoshi; Ito, Toshimichi; Togawa, Orihiko

Dai-48-Kai Kankyo Hoshano Chosa Kenkyu Seika Rombun Shorokushu (Heisei-17-Nendo), p.57 - 58, 2006/12

The authors summarized the migration behavior of particulate radionuclides in the Japan Sea as follows; (1) distributions of anthropogenic radionuclides in sediment reflect the biogecochemical cycle in the sea, (2) in the northwestern Japan Sea, particulate radionuclides in surface seawater were removed from the surface water column and transported to the deep part of the sea in spring, (3) particulate materials that are carried to the deep part of the northwestern Japan Sea are transported eastward and homogenized in the bottom layers, and (4) in the surface of the Japan Sea, most of lithogenic particles were carried through the atmosphere. These findings would play an important role to asses the factors controlling the distribution of the radionuclides in sediment in the sea.

JAEA Reports

Japan Sea expeditions for studies on water circulation and transport processes of radionuclides (Contract research)

Togawa, Orihiko; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Suzuki, Takashi

JAEA-Research 2006-004, 132 Pages, 2006/02

JAEA-Research-2006-004.pdf:7.84MB

no abstracts in English

Journal Articles

Anthropogenic radionuclides in sediment in the Japan Sea; Distribution and transport processes of particulate radionuclides

Otosaka, Shigeyoshi; Amano, Hikaru; Ito, Toshimichi; Kawamura, Hideyuki; Kobayashi, Takuya; Suzuki, Takashi; Togawa, Orihiko; Chaykovskaya, E. L.*; Lishavskaya, T. S.*; Novichkov, V. P.*; et al.

Journal of Environmental Radioactivity, 91(3), p.128 - 145, 2006/00

 Times Cited Count:14 Percentile:34.79(Environmental Sciences)

Distributions of radionuclides ($$^{90}$$Sr, $$^{137}$$Cs and $$^{239+240}$$Pu) in seabed sediment in the Japan Sea were observed during 1998-2002. Observed inventories of anthropogenic radionuclides in sediment ranged 0.1-86 Bq m$$^{-2}$$ for $$^{90}$$Sr, 23-379 Bq m$$^{-2}$$ for $$^{137}$$Cs and 0.1-86 Bq m$$^{-2}$$ for $$^{239+240}$$Pu. In the deep part ($$>$$ 2 km depth) of the western Japan Basin, $$^{239+240}$$Pu/$$^{137}$$Cs inventory ratios were larger than those in the central Yamato Basin although inventories of radionuclides were not different between basins. The higher $$^{239+240}$$Pu/$$^{137}$$Cs ratios in the western Japan Basin were derived by the production of Pu-enriched particle in the surface layer and effective sinking of particulate materials in this region. In the marginal Yamato Basin and the Ulleung Basin, both inventories and $$^{239+240}$$Pu/$$^{137}$$Cs ratios in sediment were larger than those in the central Yamato Basin. In the eastern/southern Japan Sea, it was suggested that the supply of particulate radionuclides by the TWC enhanced accumulation of radionuclides in this region.

Journal Articles

Oil spill simulation in the Japan Sea

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

WIT Transactions on Ecology and the Environment, Vol.88, p.273 - 278, 2006/00

An assessment system of marine environment in the Japan Sea is being constructed in the Japan Atomic Energy Agency. It is composed of an ocean general circulation model (RIAMOM), a particle random-walk model (SEA-GEARN) and a radiation dose assessment model (COLDOS). This study aims to confirm a validity of the assessment system by reproducing a movement of spilled oil at an incident of Russian tanker Nakhodka, in January 1997. Realistic reproduction of ocean conditions is a significant factor for accurate simulations of the movement of spilled oil. In this study, one of data assimilation techniques, an approximate Kalman filter, was introduced by combining RIAMOM with sea level measurements of satellite data. The assimilated results were in good agreement with observed oceanic phenomena both qualitatively and quantitatively. Using the calculated ocean currents, simulations of behaviour of spilled oil was performed with SEA-GEARN. The tanker was ruptured in a storm about 100 km north of the Oki Islands in Shimane Prefecture, Japan, on January 2, 1997. Most of oil spread over off Hyogo, Kyoto, Fukui and Ishikawa Prefecture, meanwhile a part of it reached a coast of Niigata Prefecture detouring around Noto Peninsula by January 21, 1997. The most important feature in these regions is considered to be a branch of the Tsushima Warm Current (TWC). Owing to a variability of TWC, ocean eddy activities and a sea surface wind, the spilled oil dispersed widely in space. On the other hand, the strong northeastward component of TWC was likely to drive the spilled oil to Niigata Prefecture. A number of experiments with different parameters and situations showed that the assimilated daily ocean currents with wind drift gave the best effect on simulation for the movement of spilled oil.

Journal Articles

Study on migration behavior of anthropogenic radionuclides in the Japan Sea, 3

Ito, Toshimichi; Otosaka, Shigeyoshi

Dai-47-Kai Kankyo Hoshano Chosa Kenkyu Seika Rombun Shorokushu (Heisei-16-Nendo), p.59 - 60, 2005/12

no abstracts in English

JAEA Reports

Studies on applications of detectors for marine radioactivity and methodologies for data analysis (Joint Research)

Ito, Toshimichi; Kinoshita, Masataka*; Saito, Saneatsu*; Machiyama, Hideaki*; Shima, Shigeki*; Gasa, Shinichi*; Togawa, Orihiko; Okano, Masaharu*

JAERI-Research 2005-028, 121 Pages, 2005/09

JAERI-Research-2005-028.pdf:12.45MB

no abstracts in English

47 (Records 1-20 displayed on this page)