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Journal Articles

Seven-year temporal variation of caesium-137 discharge inventory from the port of Fukushima Daiichi Nuclear Power Plant; Continuous monthly estimation of caesium-137 discharge in the period from April 2011 to June 2018

Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*

Journal of Nuclear Science and Technology, 57(8), p.939 - 950, 2020/08

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

After direct discharges of highly contaminated water of the Fukushima Daiichi Nuclear Power Plant (1F) from April to May 2011, Kanda suggested that relatively small amounts of run-off of radionuclides from the 1F port into the Fukushima coastal region subsequently continued by his estimation method. However, the estimation period was limited to up to September 2012. Therefore, this paper estimates the discharge inventory up to June 2018. In the missing period, the Japanese government and Tokyo Electric Power Company Holdings have continued efforts to stop the discharge, and consequently, the radionuclide concentration in seawater inside the 1F port has gradually diminished. We show the monthly discharge inventory of $$^{137}$$Cs up to June 2018 by two methods, i.e., Kanda method partially improved by the authors and a more sophisticated method using Voronoi tessellation reflecting the increase in the number of monitoring points inside the 1 F port. The results show that the former always yields overestimated results compared with the latter, but the ratio of the former to the latter is less than one order of magnitude. Using these results, we evaluate the impact of the discharge inventory from the 1F port into the coastal area and radiation dose upon fish ingestion.

Journal Articles

Predictability of a short-term emergency assessment system of the marine environmental radioactivity

Kawamura, Hideyuki; Kamidaira, Yuki; Kobayashi, Takuya

Journal of Nuclear Science and Technology, 57(4), p.472 - 485, 2020/04

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

The Japan Atomic Energy Agency developed a Short-Term Emergency Assessment system of the Marine Environmental Radioactivity (STEAMER) to predict the oceanic dispersion of radionuclides in the ocean around Japan. The purpose of this study is to validate the predictability of STEAMER using oceanographic forecast and reanalysis data, which were saved for past several years. Results of oceanic dispersion simulations that are driven by oceanographic reanalysis data are assumed to be true solutions. Oceanic dispersion simulations are conducted for Cs-137 released hypothetically from the Fukushima Daiichi Nuclear Power Plant. The predictability of STEAMER is quantitatively examined for the length of the forecast period. Ensemble forecast simulations are also conducted to successfully improve the predictability of STEAMER.

Journal Articles

Seven-year temporal variation of cesium-137 discharge inventory from the port of Fukushima Dai-ichi Nuclear Power Plant; Continuous monthly estimation of cesium-137 discharge in the period from April 2011 to June 2018

Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(4), p.226 - 236, 2019/12

After direct discharges of highly-contaminated water from Unit 2 and 3 in Fukushima Daiichi Nuclear Power Plant (1F) in April to May 2011, Kanda suggested that relatively small run-off of radionuclides from 1F port into Fukushima coastal region has subsequently continued by using his estimation scheme. However, the estimation period was limited until September 2012, and there has been no report on the issue since the work. Therefore, this paper focuses on discharge inventory from 1F port until June 2018. In the missing period, the central government and Tokyo Electric Power Company Holdings have done continuous efforts to stop the discharge, and consequently sea water concentration inside 1F port has diminished gradually. We show monthly discharge inventory of Cs-137 until June 2018 by two schemes, i.e., Kanda's scheme partially improved by authors and more sophisticated one using Voronoi tessellation reflecting the increment of the number of monitoring points inside 1F port. The results show that the former always presents overestimated results compared to the latter but the ratio of former to latter is less than one order. Based on these results, we evaluate impact of discharge inventory from 1F port into the coastal area and radiation does via fish digestion.

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

 Times Cited Count:1 Percentile:53.3(Nuclear Science & Technology)

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

Fukushima $$^{137}$$Cs releases dispersion modelling over the Pacific Ocean; Comparisons of models with water, sediment and biota data

Peri$'a$$~n$ez, R.*; Bezhenar, R.*; Brovchenko, I.*; Jung, K. T.*; Kamidaira, Yuki; Kim, K. O.*; Kobayashi, Takuya; Liptak, L.*; Maderich, V.*; Min, B. I.*; et al.

Journal of Environmental Radioactivity, 198, p.50 - 63, 2019/03

 Times Cited Count:3 Percentile:52.23(Environmental Sciences)

A number of marine radionuclide dispersion models were applied to simulate $$^{137}$$Cs releases from Fukushima Daiichi Nuclear Power Plant accident in 2011 over the northwest Pacific. Simulations extended over two years and both direct releases into the ocean and deposition of atmospheric releases on the ocean surface were considered. Dispersion models included an embedded biological uptake model (BUM). Three types of BUMs were used: equilibrium, dynamic and allometric. Model results were compared with $$^{137}$$Cs measurements in water, sediment and biota. A reasonable agreement in model/model and model/data comparisons was obtained.

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

Extended X-ray absorption fine structure study on gel/liquid extraction of f-block elements

Nakase, Masahiko*; Kobayashi, Toru; Shiwaku, Hideaki; Kawamura, Takuya*; Takeshita, Kenji*; Yamamura, Tomoo*; Yaita, Tsuyoshi

Progress in Nuclear Science and Technology (Internet), 5, p.56 - 60, 2018/11

Gel/liquid extraction was investigated to achieve selective separation of trivalent actinides over lanthanides. In this study, thermosensitive hydrogel including N,N,N',N'-tetraallylpyridine-2,6-dicarboxamine (PDA) was synthesized, and its complexation with lanthanide was investigated by extended X-ray absorption fine structure experiments at SPring-8. The radial structure functions (RSF) of solution with gels with and without ligands at different temperatures showed slight differences. As the temperature increased, the RSF decreased owing to the increase in thermal vibration, but PDA-gel showed a shift in the first peak toward the shorter direction. This shift was attributed to the change in stoichiometry of PDA-Ln(III) complexes or coordination number of water molecules affected by the change of conformation of polymer chains and the hydrophilic/hydrophobic properties in the hydrogel.

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

 Times Cited Count:0 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

 Times Cited Count:11 Percentile:8.76(Oceanography)

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

Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

Yoshigoe, Akitaka; Shiwaku, Hideaki; Kobayashi, Toru; Shimoyama, Iwao; Matsumura, Daiju; Tsuji, Takuya; Nishihata, Yasuo; Kogure, Toshihiro*; Okochi, Takuo*; Yasui, Akira*; et al.

Applied Physics Letters, 112(2), p.021603_1 - 021603_5, 2018/01

 Times Cited Count:2 Percentile:73.51(Physics, Applied)

A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, Fe) without charging issues. We found that Cs atoms were likely to be adsorbed evenly over the entire particle. Spatially-resolved X-ray absorption spectra (XAS) of the Cs M$$_{4,5}$$-edge region showed Cs to be present in a monocation state (Cs$$^{+}$$). Further pinpoint XAS measurements were also performed at the Fe L$$_{2,3}$$-edge to determine the chemical valence of the Fe atoms. Our results demonstrate the utility of SR-PEEM as a tool for spatially-resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

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:8 Percentile:56.17(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

Challenges for enhancing Fukushima environmental resilience, 7; Behavior and abundance of radiocesium in the coastal area off Fukushima

Otosaka, Shigeyoshi; Kobayashi, Takuya; Machida, Masahiko

Nippon Genshiryoku Gakkai-Shi, 59(11), p.659 - 663, 2017/11

It is estimated that about 70% of radiocesium released to the environment by the Fukushima Daiichi nuclear accident was carried to the ocean. In addition to monitoring surveys by the government, oceanographic research by many institutions has revealed the distribution and behavior of the accident-derived radiocesium in the ocean. Numerical simulations are efficiently used in such oceanographic investigations, and further improvements are being made based on findings newly obtained after the accident. In this paper, we review the abundance and behavior of radiocesium in the coastal area of Fukushima, deepen the scientific understanding of the current situation of environmental restoration, and explain the issues to be addressed in the future.

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:5 Percentile:29.98(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

Modelling of marine radionuclide dispersion in IAEA MODARIA program; Lessons learnt from the Baltic Sea and Fukushima scenarios

Peri$'a$$~n$ez, R.*; Bezhenar, R.*; Brovchenko, I.*; Duffa, C.*; Iosjpe, M.*; Jung, K. T.*; Kobayashi, Takuya; Lamego, F.*; Maderich, V.*; Min, B. I.*; et al.

Science of the Total Environment, 569-570, p.594 - 602, 2016/11

 Times Cited Count:14 Percentile:36.47(Environmental Sciences)

State-of-the art dispersion models were applied to simulate $$^{137}$$Cs dispersion from Chernobyl Nuclear Power Plant disaster fallout in the Baltic Sea and from Fukushima Daiichi Nuclear Plant releases in the Pacific Ocean after the 2011 tsunami. Models were of different nature, from box to full three-dimensional models, and included water/sediment interactions. Agreement between models was very good in the Baltic. In the case of Fukushima, results from models could be considered to be in acceptable agreement only after a model harmonization process consisting of using exactly the same forcing (water circulation and parameters) in all models. It was found that the dynamics of the considered system (magnitude and variability of currents) was essential in obtaining a good agreement between models. The difficulties in developing operative models for decision-making support in these dynamic environments were highlighted.

Journal Articles

Technical estimation for mass production of highly-concentrated $$^{rm 99m}$$Tc solution from $$^{99}$$Mo to be obtained by ($$n,gamma$$) reaction; A Preliminary study using inactive Re instead of $$^{rm 99m}$$Tc

Tanase, Masakazu*; Fujisaki, Saburo*; Ota, Akio*; Shiina, Takayuki*; Yamabayashi, Hisamichi*; Takeuchi, Nobuhiro*; Tsuchiya, Kunihiko; Kimura, Akihiro; Suzuki, Yoshitaka; Ishida, Takuya; et al.

Radioisotopes, 65(5), p.237 - 245, 2016/05

no abstracts in English

Journal Articles

A New comparison of marine dispersion model performances for Fukushima Dai-ichi releases in the frame of IAEA MODARIA program

Peri$'a$$~n$ez, R.*; Brovchenko, I.*; Duffa, C.*; Jung, K.-T.*; Kobayashi, Takuya; Lamego, F.*; Maderich, V.*; Min, B.-I.*; Nies, H.*; Osvath, I.*; et al.

Journal of Environmental Radioactivity, 150, p.247 - 269, 2015/12

 Times Cited Count:21 Percentile:27.96(Environmental Sciences)

A detailed intercomparison of marine dispersion models applied to the releases from Fukushima Dai-ichi Nuclear Power Plant has been carried out in the frame of MODARIA program, of the IAEA. Models have been compared in such a way that the reasons of the discrepancies between them can be assessed. The overall idea is to harmonize models, making them run with the same forcing in a step-by-step procedure, in such a way that the main agent in producing discrepancy between models can be found. It has been found that the main reason of discrepancies between models is due to the description of the hydrodynamics. However, once this has been suppressed, some variability between model outputs remains due to intrinsic differences between models. The numerical experiments have been carried out for a perfectly conservative radionuclide and for $$^{137}$$Cs. Model outputs for this radionuclide have also been compared with measurements in water and sediments.

JAEA Reports

Establishment of experimental system for $$^{99}$$Mo/$$^{99m}$$Tc production by neutron activation method

Ishida, Takuya; Shiina, Takayuki*; Ota, Akio*; Kimura, Akihiro; Nishikata, Kaori; Shibata, Akira; Tanase, Masakazu*; Kobayashi, Masaaki*; Sano, Tadafumi*; Fujihara, Yasuyuki*; et al.

JAEA-Technology 2015-030, 42 Pages, 2015/11

JAEA-Technology-2015-030.pdf:4.82MB

The research and development (R&D) on the production of $$^{99}$$Mo/$$^{99m}$$Tc by neutron activation method ((n, $$gamma$$) method) using JMTR has been carried out in the Neutron Irradiation and Testing Reactor Center. The specific radioactivity of $$^{99}$$Mo by (n, $$gamma$$) method is extremely low compared with that by fission method ((n,f) method), and as a result, the radioactive concentration of the obtained $$^{99m}$$Tc solution is also lowered. To solve the problem, we propose the solvent extraction with methyl ethyl ketone (MEK) for recovery of $$^{99m}$$Tc from $$^{99}$$Mo produced by (n, $$gamma$$) method. We have developed the $$^{99}$$Mo/$$^{99m}$$Tc separation/extraction/concentration devices and have carried out the performance tests for recovery of $$^{99m}$$Tc from $$^{99}$$Mo produced by (n, $$gamma$$) method. In this paper, in order to establish an experimental system for $$^{99}$$Mo/$$^{99m}$$Tc production, the R&D results of the system are summarized on the improvement of the devices for high-recovery rate of $$^{99m}$$Tc, on the dissolution of the pellets, which is the high-density molybdenum trioxide (MoO$$_{3}$$) pellets irradiated in Kyoto University Research Reactor (KUR), on the production of $$^{99m}$$Tc, and on the inspection of the recovered $$^{99m}$$Tc solutions.

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:85.84(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

Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

Katata, Genki; Chino, Masamichi; Kobayashi, Takuya; Terada, Hiroaki; Ota, Masakazu; Nagai, Haruyasu; Kajino, Mizuo*; Draxler, R.*; Hort, M.*; Malo, A.*; et al.

Atmospheric Chemistry and Physics, 15(2), p.1029 - 1070, 2015/01

 Times Cited Count:126 Percentile:1(Environmental Sciences)

We estimated a detailed time trend of atmospheric releases during the Fukushima Dai-ichi Power Station (FNPS1) accident by combining environmental monitoring data with coupling simulation of atmospheric model of WSPEEDI-II, and oceanic dispersion model of SEA-GEARN-FDM. The new scheme of dry and fogwater depositions, in-cloud scavenging, cloud condensation nuclei activity, and wet scavenging by ice phase for radioactive iodine gas and other particles was incorporated into WSPEEDI-II. The results revealed that the major releases of radionuclides occurred in the following periods: afternoon on 12 March when the wet venting and hydrogen explosion at Unit 1, morning on 13 March after the venting event at Unit 3, midnight on 14 March when three-time openings of SRV were conducted at Unit 2, morning and night on 15 March, and morning on 16 March.

151 (Records 1-20 displayed on this page)