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論文

Effect of topsoil removal and selective countermeasures on radiocesium accumulation in rice plants in Fukushima paddy field

Yang, B.*; 恩田 裕一*; 大森 良弘*; 関本 均*; 藤原 徹*; 脇山 義史*; 吉村 和也; 高橋 純子*; Sun, X.*

Science of the Total Environment, 603-604, p.49 - 56, 2017/12

 被引用回数:1 パーセンタイル:83.76(Environmental Sciences)

In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was investigated over a four-year period. The results indicate that the effect of topsoil removal measure on the accumulation of radiocesium in rice plants was effective. We summarized four year's data to further confirm that potassium and nitrogen fertilizers had an opposite effect on the accumulation of radiocesium in rice plants. Increasing potassium and reducing nitrogen fertilizer conditions tended to inhibit the radiocesium uptake by rice plants.

論文

台風201326号出水に伴う新田川起源懸濁態放射性核種の沿岸域でのインベントリ解析

内山 雄介*; 東 晃平*; 小谷 瑳千花*; 岩崎 理樹*; 津旨 大輔*; 上平 雄基; 清水 康行*; 恩田 裕一*

土木学会論文集,B2(海岸工学)(インターネット), 73(2), p.I_685 - I_690, 2017/10

福島新田川流域には原子力発電所事故直後に大量の放射性セシウム137($$^{137}$$Cs)が大気経由で沈着し、高濃度の懸濁態$$^{137}$$Csとして河道に集積したのち、出水毎に間欠的に海域へ供給され、沿岸域の底質環境に影響を与え続けている。本研究では、4段ネストJCOPE2-ROMS海洋モデル、波浪推算モデルSWAN、河川土砂流出モデルiRIC-Nays2DH、混合粒径土砂3次元海洋輸送モデル、放射性核種吸着モデルを連成させた超高解像度広域での土砂およびそれらに吸着した懸濁態$$^{137}$$Csの海洋移流分散モデリングを行い、台風201326号出水イベントに伴う新田川起源土砂の河口・沿岸域における輸送、再懸濁、堆積、浸食過程の時空間特性を評価した。その結果、台風通過直後に新田川から海域へ流入した懸濁態$$^{137}$$Csの総量の約45.3%は河口1km圏内に堆積していた。さらに、浅海域における沿岸漂砂の輸送には南方向への偏りがみられた。以上の結果は現地調査結果とも整合的であった。

論文

Time dependence of the $$^{137}$$Cs concentration in particles discharged from rice paddies to freshwater bodies after the Fukushima Daiichi NPP accident

吉村 和也; 恩田 裕一*; 若原 妙子*

Environmental Science & Technology, 50(8), p.4186 - 4193, 2016/04

 被引用回数:7 パーセンタイル:42.78(Engineering, Environmental)

Particulate radiocesium concentration in paddy fields was studied for its parameterization and temporal changes over an extensive area covering various deposition levels of radiocesium after the FDNPP accident. The particulate radiocesium concentration in the paddy field correlated with the deposition amounts, indicating that the entrainment coefficient, defined as the ratio of concentration and deposition amounts, is useful for estimating the particulate radiocesium concentration in a paddy field. Variability of the entrainment coefficient was reduced by correcting the particle size dependency of particulate radiocesium concentration. The entrainment coefficient decreased with time according to a double exponential function. The decrease rate constant of the entrainment coefficient was higher than those of other land uses, thus demonstrating a rapid decrease in the particulate radiocesium concentration in the tested paddy field.

論文

Temporal changes of radiocesium in irrigated paddy fields and its accumulation in rice plants in Fukushima

Yang, B.*; 恩田 裕一*; 脇山 義史*; 吉村 和也; 関本 均*; Ha, Y.*

Environmental Pollution, 208(Part B), p.562 - 570, 2016/01

 被引用回数:5 パーセンタイル:55.17(Environmental Sciences)

In this study, we investigated the temporal changes of radiocesium in soil, irrigation water, and rice plant in two adjacent rice paddies, with and without surface-soil-removal practice, in Fukushima Prefecture for over three years (2012 to 2014). Our results showed that radiocesium migrated into 24-28 cm soil layers and that the concentration and inventory of radiocesium in paddy soils generally decreased. The newly added radiocesium to paddies through irrigation water contributed only the maximum values of 0.15% and 0.75% of the total amount present in normal and decontaminated paddies, respectively, throughout the study period. The change trend of radiocesium concentration in suspended sediment in irrigation water exponentially decreased. Radiocesium accumulation in rice plant also decreased with time in both paddies. However, the transfer factor of radiocesium for rice plant in the decontaminated paddy increased compared with normal paddy.

論文

Behavior of accidentally released radiocesium in soil-water environment; Looking at Fukushima from a Chernobyl perspective

Konoplev, A.*; Golosov, V.*; Laptev, G.*; 難波 謙二*; 恩田 裕一*; 高瀬 つぎ子*; 脇山 義史*; 吉村 和也

Journal of Environmental Radioactivity, 151(Part 3), p.568 - 578, 2016/01

 被引用回数:27 パーセンタイル:6.18(Environmental Sciences)

Comparative analysis is provided for radiocesium wash-off parameters and Kd between suspended matter and water in rivers and surface runoff on Fukushima and Chernobyl contaminated areas for the first years after the accidents. It was found that radiocesium distribution coefficient in Fukushima rivers is essentially higher than those in Chernobyl. This can be associated with two factors: a higher RIP of samples in Fukushima and the presence of water insoluble glassy particles. It was found also that dissolved wash-off coefficients for Fukushima catchments are lower than those in Chernobyl. Particulate wash-off coefficients are comparable for Fukushima and Chernobyl. The radiocesium migration in undisturbed forest and grassland soils at Fukushima has been shown to be faster than those in Chernobyl. Investigation and analysis of radiocesium distribution in soils of Niida river catchment revealed accumulation of contaminated sediments on its floodplain.

論文

Detailed deposition density maps constructed by large-scale soil sampling for $$gamma$$-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident

斎藤 公明; 谷畑 勇夫*; 藤原 守; 齊藤 敬*; 下浦 享*; 大塚 孝治*; 恩田 裕一*; 星 正治*; 池内 嘉宏*; 高橋 史明; et al.

Journal of Environmental Radioactivity, 139, p.308 - 319, 2015/01

 被引用回数:121 パーセンタイル:0.45(Environmental Sciences)

The soil deposition density maps of $$gamma$$-ray emitting radioactive nuclides from the Fukushima Daiichi Nuclear Power Plant (NPP) accident were constructed on the basis of the results from large-scale soil sampling. The 10,915 soil samples were collected at 2,168 locations. $$gamma$$-rays emitted from the samples were measured by Ge detectors and analyzed using a reliable unified method. The determined radioactivity was corrected to that as of June 14, 2011 by taking into account the intrinsic decay constant of each nuclide. Finally the maps were created for $$^{134}$$Cs, $$^{137}$$Cs, $$^{131}$$I, $$^{129m}$$Te and $$^{110m}$$Ag. The radioactivity ratio of $$^{134}$$Cs to $$^{137}$$Cs was almost constant as 0.91 irrelevant to the soil sampling location. Effective doses for 50 years after the accident were evaluated for external and inhalation exposures due to the observed radioactive nuclides. The radiation doses from radioactive cesium were found to be much higher than those from other radioactive nuclides.

論文

Evaluation of radiocaesium wash-off by soil erosion from various land uses using USLE plots

吉村 和也; 恩田 裕一*; 加藤 弘亮*

Journal of Environmental Radioactivity, 139, p.362 - 369, 2015/01

 被引用回数:30 パーセンタイル:9.39(Environmental Sciences)

Radiocaesium wash-off associated with soil erosion in different land use was monitored using USLE plots in Kawamata, Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident. Parameters and factors relating to soil erosion and $$^{137}$$Cs concentration in the eroded soil were evaluated based on the field monitoring and presented. The erosion of fine soil, which is defined as the fraction of soil overflowed along with discharged water from a sediment-trap tank, constituted a large proportion of the discharged radiocaesium. This indicated that the quantitative monitoring of fine soil erosion is greatly important for the accurate evaluation of radiocaesium wash-off. An exponential relationship was found between vegetation cover and the amount of eroded soil. Moreover, the radiocaesium concentrations in the discharged soil were greatly affected by the land use. These results indicate that radiocaesium wash-off related to vegetation cover and land use is crucially important in modelling radiocaesium migration.

論文

An Extensive study of the concentrations of particulate/dissolved radiocaesium derived from the Fukushima Dai-ichi Nuclear Power Plant accident in various river systems and their relationship with catchment inventory

吉村 和也; 恩田 裕一*; 坂口 綾*; 山本 政儀*; 松浦 裕樹*

Journal of Environmental Radioactivity, 139, p.370 - 378, 2015/01

 被引用回数:36 パーセンタイル:6.65(Environmental Sciences)

An extensive investigation of particulate radiocaesium in suspended solids and dissolved radiocaesium in river water was undertaken at 30 sites in Fukushima and Miyagi Prefectures in December 2012, and their relationships with catchment inventory and the solid/liquid distribution coefficient ($$K_{rm d}$$) were evaluated. Rivers located in the coastal region on the north side of the Fukushima Dai-ichi Nuclear Power Plant exhibited relatively higher particulate radiocaesium concentrations. Significant correlations were found between concentrations of particulate/dissolved radiocaesium and average catchment inventories, indicating that the concentrations of particulate/dissolved radiocaesium could be approximated from the catchment inventory. Particulate radiocaesium concentration was significantly correlated with dissolved radiocaesium concentration (with the exception of concentrations measured in estuaries), and the geometric mean $$K_{rm d}$$ was calculated.

論文

Outline of the national mapping projects implemented after the Fukushima accident

斎藤 公明; 恩田 裕一*

Journal of Environmental Radioactivity, 139, p.240 - 249, 2015/01

 被引用回数:20 パーセンタイル:7.39(Environmental Sciences)

福島第一原子力発電所事故の後、国からの委託を受け原子力機構は多くの機関と協力しながらマップ事業を実施してきた。この中で、広域にわたる大規模放射線モニタリングと放射線量率等のマップ作成、環境中における放射線セシウムの移行調査とモデル化等を行なってきた。平成24年度までにマップ事業の中で得られた成果を17編の論文としてまとめ、学術雑誌Journal of Environmental Radioactivityの特集号として発刊する。本稿では、この特集号の序論として、マップ事業の全体計画、スケジュール、各調査項目の位置付け及び主要な成果について紹介する。

論文

Sediment particle size and initial radiocesium accumulation in ponds following the Fukushima DNPP accident

吉村 和也; 恩田 裕一*; 福島 武彦*

Scientific Reports (Internet), 4, p.4514_1 - 4514_6, 2014/03

 被引用回数:14 パーセンタイル:36.38(Multidisciplinary Sciences)

This study used particle size analysis to investigate the initial accumulation and trap efficiency of radiocesium ($$^{137}$$Cs) in four irrigation ponds, 4-5 months after the Fukushima Dai-ichi Nuclear Power Plant (DNPP) accident. Trap efficiency, represented by the inventory of $$^{137}$$Cs in pond sediment to the inventory of radiocesium in soil surrounding the pond (i.e., total $$^{137}$$Cs inventory), was less than 100% for all but one pond. Trap efficiency decreased as sediment particle size increased, indicating that sediments with a smaller particle size accumulate more $$^{137}$$Cs. In ponds showing low trap efficiency, fine sediment containing high concentrations of $$^{137}$$Cs appeared to be removed from the system by hydraulic flushing, leaving behind mostly coarse sediment.

口頭

福島第一原子力発電所事故に伴う放射性物質の長期的影響把握手法の確立,13; 福島県の試験水田における$$^{137}$$Csの濃度経時変化とフラックスの観測

吉村 和也; 恩田 裕一*

no journal, , 

水田において灌漑水に伴う$$^{137}$$Cs移行フラックスと浮遊砂中の$$^{137}$$Cs濃度の経時変化を観測した。灌漑水中の浮遊土砂の流入出を介した、$$^{137}$$Cs量の年間収支は-1.1$$sim$$0.1%であった。田面水、および流出水に含まれる浮遊土砂中の$$^{137}$$Cs濃度は、事故後初期(一年以内)の速やかな減少から緩やかな減少へと移っていることが示唆された。

口頭

福島県内の河川における放射性セシウムの移行状況

谷口 圭輔*; 吉村 和也; Smith, H.*; Blake, W.*; 山本 政儀*; 横山 明彦*; 高橋 嘉夫*; 坂口 綾*; 恩田 裕一*

no journal, , 

福島第一原子力発電所事故によって放出された放射性セシウムの河川を介した以降を調べるため、阿武隈川およびその支流、浜通りの二級河川に計30の観測地点を設置し、河川を介した放射性セシウムの移行の状況を継続的にモニタリングした。懸濁態、および溶存態放射性セシウム濃度は、阿武隈水系よりも浜通りの2級河川の方が高い値を示した。この違いの原因は、浜通り側の二級河川の方が、流域の放射性セシウム沈着量が多いためであると考えられる。実際、浮遊砂中のCs-137濃度と、第3次航空機モニタリング調査による流域の平均Cs-137沈着量の間に良好な正の相関関係が見ており、本調査結果と符合する。一方、河川を介した放射性セシウムのフラックスは、流量を反映して阿武隈川で浜通り側の二級河川より顕著に大きかった。

口頭

福島県内の河川における放射性セシウムの移行

谷口 圭輔*; 吉村 和也; Smith, H.*; Blake, W.*; 高橋 嘉夫*; 坂口 綾*; 山本 政儀*; 恩田 裕一*

no journal, , 

本研究では、阿武隈水系と浜通りの二級河川で採集された河川水中および浮遊砂中の放射性セシウム濃度のモニタリング結果を示し、福島県内における放射性セシウムの移行状況を報告する。放射性セシウムフラックスは、2011年9の台風15号の出水時に最も高く、その後は減少傾向にあったが。2013年の2つの台風の際には放射性セシウムフラックスは流量の増加に伴いやや高い値を示した。浮遊砂と河川水の間の放射性セシウムの分配係数には経時変化は認められなかったが、地域ごとの差異は認められた。その原因としては、流域の地質の影響などが考えられた。

口頭

Radiocesium wash-off associated with soil erosion from various land uses after the Fukushima Dai-ichi NPP accident

脇山 義史*; 恩田 裕一*; 吉村 和也; 加藤 弘亮*

no journal, , 

This study presents two-year observation of soil erosion and radiocesium wash-off to quantify differences in radiocesium behavior in various land uses. High erodibilities and relatively low values of radiocesium wash-off in cultivated farmlands can be attributed to the mixing of surface soil by ploughing. It was found that the total solid wash-off coefficient of radiocesium from farmlands is high and for 2 years period of time after the accident reaches 10%. Generally high precipitation in the region and steep slopes promote higher wash-off of radiocesium as compared to the Chernobyl case. Also, normalized wash-off coefficients exhibited relatively less volatility than erodibilities in thelandscapes. These results suggest that soil erosion management is crucial for mitigating risks of radiocesium.

口頭

道路塵埃のトレーサー物質を用いた蓬莱ダム堆積物中放射性セシウムの起源解析

Saha, M.*; 村上 道夫*; 吉村 和也; 山下 麗*; 末木 啓介*; 鯉渕 幸生*; 高田 秀重*; 恩田 裕一*

no journal, , 

本研究では、阿武隈川水系蓬莱ダム堆積物中の放射性セシウムを対象に、道路塵埃のトレーサー物質を用いることで、起源解析を行った。まず、重金属類とベンゾチアゾール類を対象に、道路塵埃のトレーサー物質としての有用性を検討した。次に、これらのトレーサー物質を用いることで、蓬莱ダム堆積物中の放射性セシウムの起源を明らかにした。

口頭

Long-term trends of plot-scale Cs-137 wash-off on various land uses in Fukushima

脇山 義史*; 恩田 裕一*; 吉村 和也; 中村 典子*; 馬目 凌*

no journal, , 

This study shows approximately three years observation results of plot-scale Cs-137 wash-off at various land uses in Kawamata town after the accident of FDNPP. Soil erosion rate were positively correlated with vegetation cover on undisturbed soils, whereas high erosion rate were found on cultivated farmlands even with similar vegetation cover to uncultivated farmlands. Annual Cs-137 wash-off rate ranged from 0.003 to 9.3 %/year and the largest was from uncultivated farmland followed by cultivated farmlands. Decreasing trends of Cs-137 concentration were found on uncultivated farmlands, whereas no trend was found on other plots. Our results suggest that the active soil erosion results in decrease in Cs-137 concentration of sediments on uncultivated slopes, while cultivation resulted in the no trend of temporal decrease in Cs-137 concentration due to constant vertical distribution of Cs-137.

口頭

Slope-scale Cs-137 wash-off processes estimated with erosion plot observations and laser-scanning

脇山 義史*; 馬目 凌*; 恩田 裕一*; 吉村 和也

no journal, , 

本研究では、斜面スケールでの土砂移動に伴う放射性セシウムの移動プロセスを明らかにすることを目的として、福島原発により放射性セシウムが沈着した地点に土壌侵食プロットを設置して土砂およびCs-137流出量の観測を行うとともにレーザープロファイラによる地表面の地形変化を追跡し、土砂移動に伴うCs-137流出の時間変化および季節性について考察を行った。本研究結果は、放射性セシウムの移行には季節性があることを示しており、将来予測の精度向上のためには斜面スケールにおけるCs-137移動プロセスについての複数年の観測が有用であることが示唆された。

口頭

Seasonality of Cs-137 concentration of sediments eroded from a slope in Fukushima

脇山 義史*; 馬目 凌*; 恩田 裕一*; 吉村 和也

no journal, , 

This study presents a three years' Cs-137 wash-off observation and morphological surveys on a soil erosion in area affected by the accident of Fukushima nuclear power plant to describe detailed processes of Cs-137 wash-off. Cs-137 concentration varied enormously and it appeared to decrease gradually from spring to autumn and increased again after winter. Based on the photos and scan data of soil surface, the expansions of a rill from spring to summer and elevations of soil surface from winter to spring were found. Our analysis suggests that freezing and thawing cycles resulted in high Cs-137 concentration of sediments during winter, whereas expansion of rill makes decrease in Cs-137 concentration in warm seasons.

口頭

Radiocesium fluxes in rivers across the Fukushima fallout region to 2015 and their controlling factors

恩田 裕一*; 谷口 圭輔*; Smith, H.*; Blake, W.*; 吉村 和也

no journal, , 

The monitoring started at 6 sites from June 2011. Subsequently, additional 24 monitoring sites were installed between October 2012 and January 2013. The total measured flux to the ocean of radiocesium from the Abukuma River at Iwanuma was 14 TBq for the period from August 2011 to October 2014. The transfer of radiocesium with suspended sediment declining until March 2015 and had high correlation with land cover ratio by different land use of the catchments. Also we found positive correlation with radiocesium flux and catchment landuses.

口頭

Land use controls fate and transport of radionuclides in Fukushima in the terrestial environment

恩田 裕一*; 谷口 圭輔*; 脇山 義史*; 吉村 和也; Smith, H.*; Blake, W.*; 岩上 翔*; 加藤 弘亮*

no journal, , 

An intensive field monitoring campaign has been started, immediately after the Fukushima NPP accident including detailed monitoring site in upstream (Yamakiya site), and 30 monitoring sites in downstream river sites. In this presentation, I will present the summary of four years environmental transfer studies after the Fukushima NPP accident. The detailed monitoring of activity concentration of radiocesium and their flux, which can be applicable for the fate and flux of the radionuclide transfer in humid temperate environment. We also found that land use controls most of the transport and then fate of Cs-137 in terrestrial environment.

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