Sakuma, Kazuyuki; Yoshimura, Kazuya; Nakanishi, Takahiro
Chemosphere, 264, p.128480_1 - 128480_9, 2021/02
We investigated characteristic of dissolved 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 Cs activity. The main results were that the deciduous broadleaf litter showed much higher leaching ratio of dissolved Cs (0.81-6.6%) than that of the coniferous needle litter (0.13-2.0%). A multi-regression analysis of Cs leaching ratios were conducted against antecedent mean precipitation and temperature, and accumulated temperature during the litterbag experiments. The model can reproduce observed Cs leaching ratios (R = 0.61-0.99).
Funaki, Hironori; Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Katengeza, E. W.*
Science of the Total Environment, 743, p.140668_1 - 140668_9, 2020/11
Misono, Toshiharu; Tsuruta, Tadahiko; Nakanishi, Takahiro; Sanada, Yukihisa; Shiribiki, Takehiko; Miyamoto, Kenji*; Urabe, Yoshimi*
JAEA-Research 2020-008, 166 Pages, 2020/10
After the accident at TEPCO Fukushima Daiichi Nuclear Power Station (1F), marine monitoring survey on radioactive substances have been conducted with financially supported by the Nuclear Regulatory Agency from FY2019. Results obtain in the project in FY2019 are presented in this report. Based on scientific grounds, the concept necessary for "progress of sea area monitoring" was arranged for the future medium- to long-term investigation of radiocesium concentrations. As basic information of survey frequency revise, a seabed topography and sediment distribution survey was conducted, and an attempt was made to understand the relationship between the seabed topography and the grain size distribution of bottom sediment. A columnar core sample was collected in the coastal area and analyzed for radioactive cesium concentration. In order to understand the dynamics of radioactive cesium contained in suspended matter flowing in from a river, suspended solids was collected using a sediment trap and the concentration of radioactive cesium was measured. We re-analyzed the towed monitoring data that had been implemented since 2013, and tried to improve the accuracy of the radioactive cesium distribution estimation map in the coastal area.
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
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.
Hagiwara, Hiroki; Nakanishi, Takahiro; Konishi, Hiromi*; Tsuruta, Tadahiko; Misono, Toshiharu; Fujiwara, Kenso; Kitamura, Akihiro
Journal of Environmental Radioactivity, 220-221, p.106294_1 - 106294_9, 2020/09
Hagiwara, Hiroki; Konishi, Hiromi*; Nakanishi, Takahiro; Fujiwara, Kenso; Iijima, Kazuki; Kitamura, Akihiro
Journal of Environmental Radioactivity, 211, p.106042_1 - 106042_10, 2020/01
Tsuji, Hideki*; Ishii, Yumiko*; Shin, M.*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Kurihara, Momo*; Yasutaka, Tetsuo*; Kuramoto, Takayuki*; Nakanishi, Takahiro; Lee, S*; et al.
Science of the Total Environment, 697, p.134093_1 - 134093_11, 2019/12
To investigate the main factors that control the dissolved radiocesium concentration in river water in the area affected by the Fukushima Daiichi nuclear power plant accident, the correlations between the dissolved Cs concentrations at 66 sites normalized to the average Cs inventories for the watersheds with the land use, soil components, topography, and water quality factors were assessed. We found that the topographic wetness index is significantly and positively correlated with the normalized dissolved Cs concentration. Similar positive correlations have been found for European rivers because wetland areas with boggy organic soils that weakly retain Cs are mainly found on plains. However, for small Japanese river watersheds, the building area ratio in the watershed strongly affected the dissolved Cs concentration.
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
We developed a simple model to evaluate and predict Cs discharge from catchment using tank model and L-Q equation. Using this model, 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 Cs discharge from catchment through rivers was a significant. However it was founded that an impact on the ocean derived from initial Cs discharge through river can be limited because 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).
Kurihara, Momo*; Yasutaka, Tetsuo*; Aono, Tatsuo*; Ashikawa, Nobuo*; Ebina, Hiroyuki*; Iijima, Takeshi*; Ishimaru, Kei*; Kanai, Ramon*; Karube, Jinichi*; Konnai, Yae*; et al.
Journal of Radioanalytical and Nuclear Chemistry, 322(2), p.477 - 485, 2019/11
We assessed the repeatability and reproducibility of methods for determining low dissolved radiocesium concentrations in freshwater in Fukushima. Twenty-one laboratories pre-concentrated three of 10 L samples by five different pre-concentration methods (prussian-blue-impregnated filter cartridges, coprecipitation with ammonium phosphomolybdate, evaporation, solid-phase extraction disks, and ion-exchange resin columns), and activity of radiocesium was measured. The z-scores for all of the Cs results were within 2, indicating that the methods were accurate. The relative standard deviations (RSDs) indicating the variability in the results from different laboratories were larger than the RSDs indicating the variability in the results from each separate laboratory.
Isotope News, (765), p.22 - 25, 2019/10
Temporal change in concentration of radiocesium in Fukushima river water are outlined. Radiocesium concentration in river water keeps decreasing after several years, however, the declining trend for the dissolved radiocesium concentration is gradually decreasing with time.
Nakanishi, Takahiro; Sato, Seiji; Matsumoto, Takumi*
Radiation Protection Dosimetry, 184(3-4), p.311 - 314, 2019/10
There has been significant concern about an increase of exposure dose in living sphere due to the accumulation of radiocesium discharged from contaminated mountainous forest in Fukushima. In this study, we investigated the history of radiocesium deposition on some floodplains in Fukushima. Radiocesium concentrations of river suspended particles and air dose rates at floodplains were also observed continuously. In many situations, annual sediment accumulation at floodplains was only several kg m and its radiocesium concentration was gradually decreasing in line with that of suspended particle. Simultaneously, air dose rates on floodplains were decreasing with time. In 2015 with heavy flood discharge, several hundred kg m of sediment accumulation and sharply decrease of air dose rate was observed at rivers without reservoir. Conversely, radiocesium accumulation at floodplain was significant reduced due to deposition on upstream reservoir.
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
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.
Nakanishi, Takahiro; Sakuma, Kazuyuki
Chemosphere, 215, p.272 - 279, 2019/01
We conducted a three-year-long observation (April 2015 - March 2018) of the 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 Cs concentration in river water in the medium term after the FDNPP accident. The dissolved and particulate Cs concentrations showed declining trends with time, even though large seasonal variations related to water temperature were also observed in the dissolved Cs concentrations. The environmental half-life for the dissolved Cs concentration was longer than previous reported values in the early phase, suggesting that the declining trend for the dissolved Cs concentration is gradually decreasing with time. The temperature dependency of the dissolved Cs concentration became weaker year by year, and the dissolved Cs concentration will likely remain at the same level for several decades.
Otosaka, Shigeyoshi; Sato, Yuhi*; Suzuki, Takashi; Kuwabara, Jun; Nakanishi, Takahiro
Journal of Environmental Radioactivity, 192, p.208 - 218, 2018/12
From August 2011 to October 2013, the concentration of iodine-129 (I) in the seabed sediment collected from 26 stations located within 160 km from the Fukushima Daiichi Nuclear Power Plant was estimated. The concentrations of I in seabed sediment off Fukushima in 2011 ranged between 0.02 and 0.45 mBq/kg. Although iodine is a biophilic element, the accident-derived radioiodine negligibly affects the benthic ecosystem. Until October 2013, a slightly increased activity of I in the surface sediment in the shelf-edge region (bottom depth: 200-400 m) was observed. The increase of the I concentrations in the shelf-edge sediments was affected by the (1) transport of I-bound particles from the land through rivers and (2) re-deposition of I desorbed from the contaminated coastal sediment to the shelf-edge sediments, which were considered to be dominant processes.
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
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 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 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 decrease in the amount of Cs in forest topsoil over the study period can be explained by radioactive decay (approximately 2.3% y), along with a migration downwards into subsoil and a small amount of export. The amount of 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.
Nakanishi, Takahiro; Oyama, Takuya; Hagiwara, Hiroki
KEK Proceedings 2017-6, p.107 - 111, 2017/11
At riverbanks in six rivers (Odaka, Ukedo, Takase, Kuma, Tomioka and Kido rivers) of eastern Fukushima, dose rate distribution in the cross section had been observed from January 2013 to December 2016. Dose rates in the flood plain which were flooded periodically were different from the surroundings. In rivers without reservoirs (Odaka, Takase and Kuma rivers), dose rates in the flood plain were affected by average radiocesium inventory in the whole catchments. By contrast, in rivers with reservoirs (Ukedo, Tomioka and Kido rivers), dose rates in the flood plain were affected by those in the downstream area of reservoirs and the erosion effect.
Tsuruta, Tadahiko; Niizato, Tadafumi; Nakanishi, Takahiro; Dohi, Terumi; Nakama, Shigeo; Funaki, Hironori; Misono, Toshiharu; Oyama, Takuya; Kurikami, Hiroshi; Hayashi, Seiji*; et al.
JAEA-Review 2017-018, 86 Pages, 2017/10
Since the accidents at Fukushima Daiichi Nuclear Power Plant following the Tohoku Region Pacific Coast Earthquake on March 11th, 2011, Fukushima Environmental Safety Center has carried out research on natural mobilization of radionuclide (especially radiocesium) and future forecast from forest to water system and surrounding residential areas. The report summarizes the latest results that have been accumulated from each study field, of our agency together with the other related research organizations. The contents of the report is to be used as evidence-based information for the QA-styled pages in the website of JAEA Sector of Fukushima Research and Development at the time of next renewal.
Koarashi, Jun; Nishimura, Shusaku; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi
Chemosphere, 165, p.335 - 341, 2016/12
We established field lysimeters in a Japanese deciduous broad-leaved forest soon after the Fukushima nuclear accident to continuously monitor the downward transfer of Cs at three depths: the litter-mineral soil boundary and depths of 5 cm and 10 cm in the mineral soil. Observations were conducted at two sites within the forest from May 2011 to May 2015. Results revealed similar temporal and depth-wise variations in Cs downward fluxes for both sites. The Cs downward fluxes generally decreased year by year at all depths, indicating that Cs was rapidly leached from the forest-floor litter layer and was then immobilized in the upper (0-5 cm) mineral soil layer through its interaction with clay minerals. The decreased inventory of mobile (or bioavailable) Cs observed during early stages after deposition indicates that the litter-soil system in the Japanese deciduous forest provides only a temporary source for Cs recycling in plants.
Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.
Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11
Particulate Cs in stream water was collected continuously for two years in order to assess the long-term trend of the Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in Cs concentration in SS.
Muto, Kotomi; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku; Koarashi, Jun; Tsuzuki, Katsunori; Nakanishi, Takahiro; Matsunaga, Takeshi
KEK Proceedings 2015-4, p.252 - 257, 2015/11
As a result of the Fukushima Daiichi Nuclear Power Plant accident, a large amount of radiocesium released into the atmosphere was deposited in forests. This study estimated the monthly trend in the fluvial discharges of radiocesium from a forest. The study site was a forested catchment in Kitaibaraki City. Radiocesium in river water was collected with a filtration system as both particulate and dissolved components. Filters and columns including dissolved Cs absorbent were replaced every month. The collected suspended solids were sieved into 2000-3000 m, 500-2000 m, 75-500 m, and 75 m fractions. The Cs concentrations in the samples were measured using -ray spectrometry with Ge semiconductor detectors. The Cs discharge increased with the river water discharge. The particulate Cs discharge was dominant in both 2013 and 2014. The Cs discharge rate of the dissolved component increased in winter, when the river water discharge decreased.