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Journal Articles

Impact of extreme typhoon events on the fluvial discharge of particulate radiocesium in Fukushima Prefecture

Nakanishi, Takahiro; Oyama, Takuya; Hagiwara, Hiroki; Sakuma, Kazuyuki

Journal of Coastal Research, 114(SI), p.310 - 314, 2021/10

The two huge typhoons in 2019, Hagibis and Bualoi, caused enormous flood damage to Fukushima. On the basis of field observations over 6 years in Ukedo River near the Fukushima Nuclear Power Plant, sediment and $$^{137}$$Cs discharges from the river catchment were quantitatively evaluated. Approximately 90% of annual sediment and $$^{137}$$Cs discharges in 2019 was occupied during the typhoons Hagibis and Bualoi events. This sediment discharge was almost twice than the discharge during the largest ever flood event since the Fukushima nuclear accident, caused by typhoon Etau in September 2015. However, $$^{137}$$Cs discharge during Hagibis and Bualoi events was two-thirds that of Etau event, because the particulate $$^{137}$$Cs concentration in river water decreased during the observation period. Moreover, $$^{137}$$Cs discharge during two typhoon events in 2019 accounted for only 0.1% of the catchment $$^{137}$$Cs deposition and the impact of radiocesium to the coastal area was extremely limited.

Journal Articles

Factors affecting $$^{137}$$Cs concentrations in river water under base-flow conditions near the Fukushima Dai-ichi Nuclear Power Plant

Nakanishi, Takahiro; Funaki, Hironori; Sakuma, Kazuyuki

Journal of Radioanalytical and Nuclear Chemistry, 328(3), p.1243 - 1251, 2021/06

 Times Cited Count:0 Percentile:0.01(Chemistry, Analytical)

To confirm factors affecting $$^{137}$$Cs concentration in river water after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, this study conducted monthly observations of nine rivers near the FDNPP from April 2017 to March 2018 under base-flow conditions. The annual mean dissolved and particulate $$^{137}$$Cs concentrations correlated well with the mean $$^{137}$$Cs deposition in the catchment. The normalized $$^{137}$$Cs concentrations in both phases by dividing by the mean $$^{137}$$Cs deposition in the catchment showed significant negative correlations with the $$^{137}$$Cs deposition ratio for forests. The inflow from the downstream plain areas increased the $$^{137}$$Cs concentrations near the FDNPP.

Journal Articles

Leaching characteristics of $$^{137}$$Cs for forest floor affected by the Fukushima nuclear accident; A Litterbag experiment

Sakuma, Kazuyuki; Yoshimura, Kazuya; Nakanishi, Takahiro

Chemosphere, 264, p.128480_1 - 128480_9, 2021/02

 Times Cited Count:2 Percentile:0(Environmental Sciences)

We investigated characteristic of dissolved $$^{137}$$Cs leaching from litters collected at a coniforest needle and a deciduous broadleaf forests using litterbags at upstream area of Ohta River in Fukushima. Each leaf type of litters was collected into 36 litterbags, respectively, and installed each forest floor in June and December, 2017. Triplicate samples were collected at each forest floor and readily transported to the laboratory in August, December, 2017 and March, May, August, December, 2018. Samples were put in buckets and soaked in purified water. We took leaching water samples from the buckets at 20 min, 140 min, 1 day after soaking litter samples in the water. These samples were analysed about $$^{137}$$Cs activity. The main results were that the deciduous broadleaf litter showed much higher leaching ratio of dissolved $$^{137}$$Cs (0.81-6.6%) than that of the coniferous needle litter (0.13-2.0%). A multi-regression analysis of $$^{137}$$Cs leaching ratios were conducted against antecedent mean precipitation and temperature, and accumulated temperature during the litterbag experiments. The model can reproduce observed $$^{137}$$Cs leaching ratios (R$$^{2}$$ = 0.61-0.99).

Journal Articles

Calculations for ambient dose equivalent rates in nine forests in eastern Japan from $$^{134}$$Cs and $$^{137}$$Cs radioactivity measurements

Malins, A.; Imamura, Naohiro*; Niizato, Tadafumi; Takahashi, Junko*; Kim, M.; Sakuma, Kazuyuki; Shinomiya, Yoshiki*; Miura, Satoru*; Machida, Masahiko

Journal of Environmental Radioactivity, 226, p.106456_1 - 106456_12, 2021/01

 Times Cited Count:0 Percentile:0(Environmental Sciences)

Journal Articles

Reservoir sediments as a long-term source of dissolved radiocaesium in water system; a mass balance case study of an artificial reservoir in Fukushima, Japan

Funaki, Hironori; Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Katengeza, E. W.*

Science of the Total Environment, 743, p.140668_1 - 140668_9, 2020/11

 Times Cited Count:5 Percentile:39.03(Environmental Sciences)

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018) (Translated document)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2020-007, 249 Pages, 2020/10

JAEA-Research-2020-007.pdf:15.83MB

The accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Journal Articles

Simulation study of the effects of buildings, trees and paved surfaces on ambient dose equivalent rates outdoors at three suburban sites near Fukushima Dai-ichi

Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Journal of Environmental Radioactivity, 210, p.105803_1 - 105803_10, 2019/12

 Times Cited Count:3 Percentile:20.11(Environmental Sciences)

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of $$gamma$$ rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Numerical study of transport pathways of $$^{137}$$Cs from forests to freshwater fish living in mountain streams in Fukushima, Japan

Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Sasaki, Yoshito; Niizato, Tadafumi

Journal of Environmental Radioactivity, 208-209, p.106005_1 - 106005_11, 2019/11

 Times Cited Count:8 Percentile:57.6(Environmental Sciences)

To assess the uptake of Cs-137 ($$^{137}$$Cs) by freshwater fish, we developed a compartment model for the migration of $$^{137}$$Cs on the catchment scale from forests to river water. We modelled a generic forest catchment with Fukushima-like parameters to ascertain the importance of export pathways of $$^{137}$$Cs from forests to river water for the uptake of $$^{137}$$Cs by freshwater fish. The results suggest that the decreasing trend of $$^{137}$$Cs in river water and freshwater fish was due to combination of the decreasing trend in the forest leaves/needles and litter compartments, and the increasing trend in soil. The $$^{137}$$Cs concentrations within these forest compartments plateau at around ten years after the fallout due to $$^{137}$$Cs circulation in forests reaching an equilibrium state.

Journal Articles

A Modeling approach to estimate the $$^{137}$$Cs discharge in rivers from immediately after the Fukushima accident until 2017

Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Kurikami, Hiroshi; Namba, Kenji*; Zheleznyak, M.*

Journal of Environmental Radioactivity, 208-209, p.106041_1 - 106041_12, 2019/11

 Times Cited Count:4 Percentile:37.91(Environmental Sciences)

We developed a simple model to evaluate and predict $$^{137}$$Cs discharge from catchment using tank model and L-Q equation. Using this model, $$^{137}$$Cs discharge and discharge ratio from Abukuma River and 13 other rivers in Fukushima coastal region were estimated from immediately after Fukushima accident to 2017. Cesium-137 discharge ratio to the deposition amount in catchment through Abukuma River and 13 other rivers in Fukushima coastal region during about initial six months were estimated to be 18 TBq (3.1%) and 11 TBq (0.8%), respectively. These values were 1-2 orders of magnitude larger than the previous study observed after June 2011, indicating that initial $$^{137}$$Cs discharge from catchment through rivers was a significant. However it was founded that an impact on the ocean derived from initial $$^{137}$$Cs discharge through river can be limited because $$^{137}$$Cs discharge from Abukuma River and 13 other rivers in Fukushima coastal region (29 TBq) was two orders of magnitude smaller than the direct release from FDNPP into the ocean (3.5 PBq) and from atmospheric deposition into the ocean (7.6 PBq).

Journal Articles

Research and development behind a computation system for 3D distributions of air dose rates in the environment; Estimating environmental radiation doses using PHITS together with remote sensing data

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Isotope News, (765), p.30 - 33, 2019/10

Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2019-002, 235 Pages, 2019/08

JAEA-Research-2019-002.pdf:21.04MB

The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Journal Articles

Trend of $$^{137}$$Cs concentration in river water in the medium term and future following the Fukushima Nuclear accident

Nakanishi, Takahiro; Sakuma, Kazuyuki

Chemosphere, 215, p.272 - 279, 2019/01

 Times Cited Count:20 Percentile:88.35(Environmental Sciences)

We conducted a three-year-long observation (April 2015 - March 2018) of the $$^{137}$$Cs concentration in two rivers affected by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. The result revealed a declining trend for the dissolved and particulate $$^{137}$$Cs concentration in river water in the medium term after the FDNPP accident. The dissolved and particulate $$^{137}$$Cs concentrations showed declining trends with time, even though large seasonal variations related to water temperature were also observed in the dissolved $$^{137}$$Cs concentrations. The environmental half-life for the dissolved $$^{137}$$Cs concentration was longer than previous reported values in the early phase, suggesting that the declining trend for the dissolved $$^{137}$$Cs concentration is gradually decreasing with time. The temperature dependency of the dissolved $$^{137}$$Cs concentration became weaker year by year, and the dissolved $$^{137}$$Cs concentration will likely remain at the same level for several decades.

Journal Articles

Evaluation of particulate $$^{137}$$Cs discharge from a mountainous forested catchment using reservoir sediments and sinking particles

Funaki, Hironori; Yoshimura, Kazuya; Sakuma, Kazuyuki; Iri, Shatei; Oda, Yoshihiro

Journal of Environmental Radioactivity, 189, p.48 - 56, 2018/09

 Times Cited Count:7 Percentile:42.65(Environmental Sciences)

Journal Articles

Development of the evaluation tool for air dose rate in forest using a Monte Carlo radiation transport code (PHITS)

Sakuma, Kazuyuki; Niizato, Tadafumi; Kim, M.; Malins, A.; Machida, Masahiko; Yoshimura, Kazuya; Kurikami, Hiroshi; Kitamura, Akihiro; Hosomi, Masaaki*

Kankyo Hoshano Josen Gakkai-Shi, 6(3), p.145 - 152, 2018/09

We simulated air dose rates using PHITS to consider how the partitioning of radiocesium between the forest canopy, litter layer and soil layer affected air dose rates by perturbing the radiocesium source distribution between different simulations. Transferring radiocesium from the canopy to the litter layer did not affect air dose rates at 1 m above the ground when setting up the simulation with a radiocesium distribution measured in October 2015. This is because there was almost no radiocesium in the canopy at that time. However air dose rates tended to be high near the canopy, and above the canopy up to 200 m altitude, when the simulations were initiated using source distribution data applicable for August-September 2011, due to the larger amount of radiocesium in the canopy at that time. Transferring the radiocesium from the canopy to the litter layer in this case was associated with a three times increase in the air dose rate at 1 m, as the average distance between radiocesium in the forest and 1 m above the ground was shortened. In both cases radiocesium transfer from the litter layer to the underlying soil was associated with a one third to 50% reduction in air dose rates at 1 m, due to the self-shielding effect of soil.

Journal Articles

Development of an air dose rate evaluation system (3D-ADRES) for complex real environments in Fukushima Prefecture; Using remote sensing data and evaluating the influence of different features (topography, soil, buildings, trees, etc.)

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

RIST News, (64), p.3 - 16, 2018/09

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of $$gamma$$ rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Applicability of $$K_{d}$$ for modelling dissolved $$^{137}$$Cs concentrations in Fukushima river water; Case study of the upstream Ota River

Sakuma, Kazuyuki; Tsuji, Hideki*; Hayashi, Seiji*; Funaki, Hironori; Malins, A.; Yoshimura, Kazuya; Kurikami, Hiroshi; Kitamura, Akihiro; Iijima, Kazuki; Hosomi, Masaaki*

Journal of Environmental Radioactivity, 184-185, p.53 - 62, 2018/04

 Times Cited Count:2 Percentile:13.2(Environmental Sciences)

A study is presented on the applicability of the distribution coefficient ($$K_{d}$$) absorption/desorption model to simulate dissolved $$^{137}$$Cs concentrations in Fukushima river water. The simulation results were in good agreement with the observations on water and suspended sediment fluxes, and on particulate bound $$^{137}$$Cs concentrations under both ambient and high flow conditions. By contrast the measured concentrations of dissolved $$^{137}$$Cs in the river water were much harder to reproduce with the simulations. By tuning the $$K_{d}$$ values for large particles, it was possible to reproduce the mean dissolved $$^{137}$$Cs concentrations during base flow periods (observation: 0.32 Bq/L, simulation: 0.36 Bq/L). However neither the seasonal variability in the base flow dissolved $$^{137}$$Cs concentrations (0.14-0.53 Bq/L), nor the peaks in concentration that occurred during storms (0.18-0.88 Bq/L, mean: 0.55 Bq/L), could be reproduced with realistic simulation parameters.

Journal Articles

Evaluation of sediment and $$^{137}$$Cs redistribution in the Oginosawa River catchment near the Fukushima Dai-ichi Nuclear Power Plant using integrated watershed modeling

Sakuma, Kazuyuki; Malins, A.; Funaki, Hironori; Kurikami, Hiroshi; Niizato, Tadafumi; Nakanishi, Takahiro; Mori, Koji*; Tada, Kazuhiro*; Kobayashi, Takamaru*; Kitamura, Akihiro; et al.

Journal of Environmental Radioactivity, 182, p.44 - 51, 2018/02

 Times Cited Count:7 Percentile:42.65(Environmental Sciences)

The Oginosawa River catchment lies 15 km south-west of the Fukushima Dai-ichi nuclear plant. The General-purpose Terrestrial Fluid-flow Simulator (GETFLOWS) code was used to study sediment and $$^{137}$$Cs redistribution within the catchment. Cesium-137 input to watercourses came predominantly from land adjacent to river channels and forest gullies. Forested areas far from the channels only made a minor contribution to $$^{137}$$Cs input to watercourses, total erosion of between 0.001-0.1 mm from May 2011 to December 2015. The 2.3-6.9% y$$^{-1}$$ decrease in the amount of $$^{137}$$Cs in forest topsoil over the study period can be explained by radioactive decay (approximately 2.3% y$$^{-1}$$), along with a migration downwards into subsoil and a small amount of export. The amount of $$^{137}$$Cs available for release from land adjacent to rivers is expected to be lower in future than compared to this study period, as the simulations indicate a high depletion of inventory from these areas.

Journal Articles

Characteristics of radio-cesium transport and discharge between different basins near to the Fukushima Dai-ichi Nuclear Power Plant after heavy rainfall events

Sakuma, Kazuyuki; Kitamura, Akihiro; Malins, A.; Kurikami, Hiroshi; Machida, Masahiko; Mori, Koji*; Tada, Kazuhiro*; Kobayashi, Takamaru*; Tawara, Yasuhiro*; Tosaka, Hiroyuki*

Journal of Environmental Radioactivity, 169-170, p.137 - 150, 2017/04

 Times Cited Count:18 Percentile:69.64(Environmental Sciences)

This paper describes watershed modeling of catchments surrounding the Fukushima Dai-ichi Nuclear Power Plant to understand radio-cesium redistribution by water flows and sediment transport. We extended our previously developed three-dimensional hydrogeological model of the catchments to calculate the migration of radio-cesium in both sediment-sorbed and dissolved forms. The simulations cover the entirety of 2013, including nine heavy rainfall events, as well as Typhoon Roke in September 2011. Typhoons Man-yi and Wipha were the strongest typhoons in 2013 and had the largest bearing on radio-cesium redistribution. The simulated $$^{137}$$Cs discharge quantities over the nine events in 2013 are in good agreement with field monitoring observations. Deposition mainly occurs on flood plains and points where the river beds broaden in the lower basins, and within dam reservoirs along the rivers. Differences in $$^{137}$$Cs discharge ratios between the five basins are explained by differences in the initial fallout distribution within the basins, the presence of dam reservoirs, and the input supply to watercourses. It is possible to use these simulation results to evaluate future radioactive material distributions in order to support remediation planning.

Journal Articles

Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding

Kitamura, Akihiro; Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Okumura, Masahiko; Machida, Masahiko; Mori, Koji*; Tada, Kazuhiro*; Tawara, Yasuhiro*; Kobayashi, Takamaru*; et al.

Earth Surface Processes and Landforms, 41(12), p.1708 - 1726, 2016/09

 Times Cited Count:14 Percentile:62.25(Geography, Physical)

Sediment erosion and transport processes that are considered to be important in predicting the future radioactive material distribution through sediment-sorbed form in Fukushima Prefecture are simulated. Since large portion of the sediment is considered to be supplied into the rivers, it is important to trace their migration process in terms of each river basin. We choose five river basins, namely the Odaka, the Ukedo, the Maeda, the Kuma, and the Tomioka, from north to south, because of their importance in contamination aspects and prediction studies. The results are summarized as comprehensive dataset of sediment migration for particular river basins in typical typhoon events that account for the most of annual soil erosion. Detail calculations implemented for the amount of sediment supplied in to the river, deposited on river and dam beds, and exported to the ocean.

Oral presentation

Mathematical modeling of radio-cesium migrations and air dose rate changes in eastern Fukushima Prefecture

Kitamura, Akihiro; Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Okumura, Masahiko; Itakura, Mitsuhiro; Yamada, Susumu; Machida, Masahiko

no journal, , 

Radioactive cesium that was deposited over Fukushima after the accident at the FDNPP is one of the major concerns regarding health physics. In order to predict the future distribution of radioactive cesium and resulting air dose rate at any location in Fukushima, we have integrated a number of mathematical models covering different time and scales. We present simulation results of sediment movement and radioactive cesium migration using semi empirical and physics based watershed models, and that of sediment and radioactive cesium behavior in a dam reservoir using one and two dimensional river simulation models. We also present a tool for calculating air dose rates from arbitrary radio cesium depth profiles and spatial distributions. The predicted dose rates were compared against dose rates measured in the field with handheld survey meters and good correlation was found between the two.

61 (Records 1-20 displayed on this page)