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Ikenoue, Tsubasa; Nakanishi, Takahiro; Shimadera, Hikari*; Kawamura, Hideyuki; Kondo, Akira*
E3S Web of Conferences (Internet), 530, p.02005_1 - 02005_10, 2024/05
The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) caused a radioactive contamination in seabed sediment. The Cs supply from rivers could be an important process for the long-term behavior of
Cs in seabed sediment. In this study, a ten-year simulation of the
Cs behavior in seabed sediment was conducted using an oceanic dispersion model combined with a prediction model of
Cs behavior in land and river. In the waters north of FDNPP, the simulation results suggested that the
Cs supply from rivers had a great impact on the concentrations in coastal sediment due to the initial low concentrations in seabed sediment and the large supply of
Cs from rivers. In the waters near FDNPP and south of FDNPP, the simulation results suggested that the impact of the
Cs supply on the temporal variation of
Cs concentration in coastal sediment was relatively small due to the large initial adsorption from seawater. Overall, these results indicated that
Cs supply from rivers had an impact on the spatiotemporal distribution of
Cs concentrations in seabed sediment on a decadal time scale and the impact was especially great in the waters north of FDNPP.
Ikenoue, Tsubasa; Shimadera, Hikari*; Nakanishi, Takahiro; Kondo, Akira*
Water (Internet), 15(15), p.2734_1 - 2734_18, 2023/08
Times Cited Count:0 Percentile:0.00(Environmental Sciences)The Fukushima Daiichi Nuclear Power Plant accident caused an accumulation of Cs in coastal sediment. The
Cs supply from rivers to the ocean can affect the long-term fate of
Cs in coastal sediment. Since the Fukushima coastal river basins include large decontaminated and evacuation order areas, considering the decontamination work and resumption of agriculture is important for predicting the
Cs supply. We conducted a 30-year prediction of the
Cs supply from the Fukushima coastal rivers to the ocean using a distributed radiocesium prediction model, considering the effects of human activities. In river basins with decontaminated and evacuation order areas, human activities reduced the total
Cs outflow from agricultural lands, urban lands, and forest areas to the rivers and the
Cs supply to the ocean by 5.0% and 6.0%, respectively. These results indicated that human activities slightly impacted the
Cs outflow and supply. The
Cs supply from rivers impacted by the accident to the coastal sediment was estimated to correspond to 11-36% of the total
Cs in the coastal sediment in the early phase of the accident. Therefore, the
Cs supply from rivers to the ocean is important for the long-term behavior of
Cs in coastal sediment.
Ikenoue, Tsubasa; Shimadera, Hikari*; Nakanishi, Takahiro; Kondo, Akira*
Science of the Total Environment, 876, p.162846_1 - 162846_12, 2023/06
Times Cited Count:4 Percentile:46.73(Environmental Sciences)We conducted 30 years simulation of environmental fate of Cs in the Abukuma River basin considering the characteristics of the
Cs behavior in land uses. Overall, in the Abukuma River basin, the
Cs transported into the ocean for 30 years was estimated to correspond to 4.6% of the initial deposition in the basin, and the effective half-life of
Cs deposited in the basin was estimated to be 3.7 years shorter (by 11.6%) than its physical half-life. These results suggested that
Cs deposited from the accident could still remain for decades. Based on the analysis of the
Cs behavior in land use, in 2011, the contribution of
Cs export to the ocean from urban lands was estimated to correspond to 70% of the total
Cs export. Meanwhile, from 2012 to 2040, the contribution of
Cs export from agricultural lands was estimated to correspond to 75% of the total
Cs export. The reduction ratios excluding radioactive decay of
Cs remained in areas with and without human activities for 30 years after the accident, defined as the ratios of the total outflow to the initial deposition, were estimated to be 11.5%-17.7% and 0.4%-1.4%, respectively. These results suggested that human activities enhance the reduction of
Cs remaining in land in the past and future.
Ikenoue, Tsubasa; Kawamura, Hideyuki; Kamidaira, Yuki
Journal of Nuclear Science and Technology, 60(1), p.61 - 71, 2023/01
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)We conducted numerical simulations on the oceanic dispersion of dissolved radionuclide hypothetically released from the Fukushima Dai-ichi Nuclear Power Plant using long-term oceanographic reanalysis data. We evaluated the characteristics and trends of dissolved radionuclide behavior in the ocean using statistical analysis based on the simulation results. The surface meridional current at the release point in the Fukushima coastal ocean and the Kuroshio Extension significantly affected the north-south transport of the surface radionuclide in the Fukushima coastal ocean and the eastward transport of the offshore surface radionuclide, respectively. Because the surface kinetic energy in the coastal to the offshore area was larger, the range of the dispersed surface radionuclide tended to be larger. In summer (July-September), the increased frequency radionuclide entrainment by the Kuroshio Extension because of the surface southward radionuclide transport in the Fukushima coastal ocean and the large surface kinetic energy caused a large dispersed surface radionuclide. In winter (January-March), the decreased frequency radionuclide entrainment by the Kuroshio Extension because of the surface northward radionuclide transport in the Fukushima coastal ocean and the small surface kinetic energy caused a small dispersed surface radionuclide.
Otosaka, Shigeyoshi*; Kamidaira, Yuki; Ikenoue, Tsubasa; Kawamura, Hideyuki
Journal of Nuclear Science and Technology, 59(4), p.409 - 423, 2022/04
Times Cited Count:5 Percentile:50.16(Nuclear Science & Technology)After the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP), many oceanographic observations were carried out from various perspectives. Numerical simulations were also effectively applied to understand the distribution of radionunclides. By integrating these results, the dynamics of the accident-derived radionuclides in the ocean were highlighted. The transport processes of the accident-derived radionuclides to the ocean include (1) direct discharge to the ocean, (2) deposition in the ocean via the atmosphere, and (3) inflow from rivers after deposition to the land surface. In the case of Cs, one of major accident-derived radionuclides, most of the supply to the ocean immediately after the accident (8-21 PBq) was estimated to be due to processes (1) and (2). The amount of
Cs accumulated on the seafloor is only about 1% (0.2PBq) of the amount carried to the ocean, but it remains in the sediments in the coastal area for a long period of time and gradually migrates to the seawater and ecosystems near the seafloor.
Ikenoue, Tsubasa; Shimadera, Hikari*; Kondo, Akira*
Journal of Environmental Radioactivity, 225, p.106452_1 - 106452_12, 2020/12
Times Cited Count:5 Percentile:18.67(Environmental Sciences)This study focused on the uncertainty of the factors of the Universal Soil Loss Equation (USLE) and evaluated its impacts on the environmental fate of Cs simulated by a radiocesium transport model in the Abukuma River basin. The USLE has five physically meaningful factors: the rainfall and runoff factor (R), soil erodibility factor (K), topographic factor (LS), cover and management factor (C), and support practice factor (P). The simulation results showed total suspended sediment and
Cs outflows were the most sensitive to C and P among the all factors. Therefore, land cover and soil erosion prevention act have the great impact on outflow of suspended sediment and
Cs. Focusing on land use, the outflow rates of
Cs from the forest areas, croplands, and undisturbed paddy fields were large. This study indicates that land use, especially forest areas, croplands, and undisturbed paddy fields, has a significant impact on the environmental fate of
Cs.
Koike, Taichi*; Ikenoue, Tsubasa; Koga, Yutaro*; Matsuo, Tomohito*; Shimadera, Hikari*
no journal, ,
Accurate estimation of nutrient load from land is necessary for nutrient management in the enclosed coastal sea of Harimanada with oligotrophication problem. We aim to accurately estimate the nutrient load including the rapid increase during flood events in the Kako River basin, which has the largest basin area among the rivers flowing into the Harimanada. In this study, we estimated suspended solid (SS) load during flood events using a water quality model incorporated with the soil erosion process and evaluated its accuracy. As a result, although there is room for improvement in the height of the peak and the timing, the increase in SS load during Flood Events was generally reproduced.
Nittono, Akira*; Ikenoue, Tsubasa; Shimadera, Hikari*; Matsuo, Tomohito*; Kondo, Akira*
no journal, ,
The Fukushima Daiichi Nuclear Power Plant accident caused extensive Cs contamination. Long-term simulations have been conducted to predict the amount of
Cs outflow from river basins to the ocean. However, there are uncertainties about the influences of rainfall, tree types and dams to the
Cs outflow. This study focused on how much these three factors influence the
Cs outflow in eastern Fukushima river basins from 2011 to 2040. The
Cs outflow varied by -10 to +17% depending on precipitation, and by -16 to +19% depending on tree species, decreased by 21% by dams.
Ikenoue, Tsubasa
no journal, ,
We report the results of a recent simulation study by JAEA on the behavior of radiocesium (Cs) released by the Fukushima Daiichi Nuclear Power Plant accident (1F accident) near the coastal seafloor. The
Cs supply from rivers could be an important process for the long-term behavior of
Cs in seabed sediment. In this study, we conducted a simulation to predict the behavior of
Cs in seabed sediment by combining an ocean dispersion model with a river model. Based on the simulation results, we explain the impact of
Cs supply from rivers on the long-term behavior of
Cs in seabed sediment.
Ikenoue, Tsubasa; Kawamura, Hideyuki; Kamidaira, Yuki
no journal, ,
In this study, we analyzed the characteristics and trends of oceanic dispersal of Cs by performing the oceanic dispersion simulations using past oceanographic data received on the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) developed at JAEA. Oceanic dispersion simulations in 1461 cases were carried out in the northwestern Pacific Ocean for 60 days from every day between 2015 and 2018. It was assumed that
Cs was released into the ocean from the Fukushima Dai-ichi Nuclear Power Plant. In all calculation cases, the maximum concentration in 30 days at each computational grid (maximum concentration distribution) was calculated.
Cs in the ocean surface in winter tended to be not dispersed so much. In the ocean surface, the seasonal variation was greater than the annual variation though the maximum concentration distributions have little annual variation. The average of the maximum concentration distribution in all calculation cases was inclined to be high from the coast of Fukushima to the offshore (140
E-145
E) and near the Kuroshio Extension.
Ikenoue, Tsubasa; Shimadera, Hikari*; Kondo, Akira*
no journal, ,
We evaluated the environmental fate of Cs in the Abukuma River Basin from 2011 to 2040 by using a distributed radiocesium prediction model. The model well reproduced interannual variations in the concentration of
Cs in the suspended sediment and the total outflow of
Cs at Iwanuma near the estuary. Thirty years after the Fukushima Daiichi Nuclear Power Plant accident, it was estimated that the concentration of
Cs in the suspended sediment decreased to 1.9% of the concentration in the earliest phase after the accident and the total outflow of
Cs was equivalent to 4.6% of the initial deposition in the Abukuma River basin.
Ikenoue, Tsubasa; Shimadera, Hikari*; Kondo, Akira*
no journal, ,
This study focused on the uncertainty of the factors of the USLE and evaluated its impacts on the environmental fate of Cs simulated by a radiocesium transport model in the Abukuma River basin. In the USLE, soil loss is expressed as a product of factors representing rainfall (R factor), geology (K factor), topographic (L
S factor) and land cover and soil erosion prevention act (C
P factor). The simulation results showed total outflows of suspended sediment and
Cs were the most sensitive to C
P factor among the all factors. Therefore, land cover and soil erosion prevention methods have the great impact on outflow of suspended sediment and
Cs.
Ikenoue, Tsubasa; Nakanishi, Takahiro; Kawamura, Hideyuki
no journal, ,
The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 resulted in the release of radionuclides in the marine environment. Among the radionuclides released, since large quantities of Cs were released and
Cs has a long half-life, there is concern about the impacts of
Cs on marine environment. Most of
Cs is dissolved in seawater, but some
Cs is taken in and adsorbed on biogenic particles (phytoplankton, zooplankton, and detritus). In this study, we aim to predict the long-term fate of
Cs in ocean considering migration process of
Cs in a lower trophic level ecosystem. We improved an oceanic dispersion model by coupling with a lower trophic level ecosystem model and conducted the long-term simulation of
Cs in ocean. This improvement enabled the long-term prediction of
Cs concentrations in biogenic particles and organic seabed sediment as well as in seawater. The calculation results suggested that the adsorption process from seawater to organic sediment had a much greater impact on
Cs concentration in organic seabed sediment than the sedimentation process of biogenic particles.