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Journal Articles

Validation study of ambient dose equivalent conversion coefficients for radiocaesium distributed in the ground; Lessons from the Fukushima Daiichi Nuclear Power Station accident

Ochi, Kotaro; Funaki, Hironori; Yoshimura, Kazuya; Iimoto, Takeshi*; Matsuda, Norihiro; Sanada, Yukihisa

Radiation and Environmental Biophysics, 61(1), p.147 - 159, 2022/03

Journal Articles

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Funaki, Hironori; Tsuji, Hideki*; Nakanishi, Takahiro; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Science of the Total Environment, 812, p.152534_1 - 152534_10, 2022/03

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the $$^{137}$$Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable $$^{137}$$Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between $$^{137}$$Cs and NH$$_{4}$$ via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.

Journal Articles

Characterization of radiocesium-bearing microparticles with different morphologies in soil around the Fukushima Daiichi Nuclear Power Plant

Hagiwara, Hiroki; Funaki, Hironori; Shiribiki, Natsu*; Kanno, Marina*; Sanada, Yukihisa

Journal of Radioanalytical and Nuclear Chemistry, 331(1), p.415 - 426, 2022/01

Journal Articles

Radiocesium transfer into freshwater planktonic ${it Chlamydomonas}$ spp. microalgae in a pond near the Fukushima Dai-ichi Nuclear Power Plant

Sasaki, Yoshito; Funaki, Hironori; Fujiwara, Kenso

Limnology, 23(1), p.1 - 7, 2022/01

We investigated the transfer behavior of radiocesium in living cells and remains of a bloom of microalgae (${it Chlamydomonas}$ sp.) in a pond located about 5 km from the Fukushima Dai-ichi Nuclear Power Plant. As a positive correlation was detected between the cell number of microalgae and the radiocesium concentration (Bq/L) in the $$>$$ 0.45-$$mu$$m fraction, microalgae were the controlling factor for the radiocesium concentration of the $$>$$ 0.45-$$mu$$m fraction. The transfer factor of water-to-algae [($$^{137}$$Cs concentration Bq/kg $$>$$ 0.45-$$mu$$m fraction) $$times$$ ($$^{137}$$Cs concentration Bq/L water)$$^{-1}$$] was 1.6 $$times$$ 10$$^{3}$$. The radiocesium concentration of microalgae remains was the same as that in intact cells.

Journal Articles

Design, construction and monitoring of temporary storage facilities for removed contaminants

Saegusa, Hiromitsu*; Funaki, Hironori; Kurikami, Hiroshi; Sakamoto, Yoshiaki; Tokizawa, Takayuki*

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.170 - 187, 2021/10

Removed contaminants including soil, grass and trees are to be stored safely at temporary storage facilities for several years, after which they will be transferred to a planned interim storage facility. The decontamination pilot project was carried out in both the restricted and planned evacuation areas in order to assess decontamination methods and demonstrate measures for radiation protection of workers. Fourteen temporary storage facilities of different technical specifications were designed and constructed under various topographic conditions and land use. In order to support the design, construction and monitoring of temporary storage facilities for removed contaminants during the full-scale decontamination within the prefecture of Fukushima, technical know-how obtained during the decontamination pilot project has been identified and summarized in this paper.

Journal Articles

Dynamics of $$^{137}$$Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi Nuclear Power Plant Accident

Tsuji, Hideki*; Nakagawa, Megumi*; Iijima, Kazuki; Funaki, Hironori; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Global Environmental Research (Internet), 24(2), p.115 - 127, 2021/06

Lake water, phytoplankton and zooplankton were sampled by a total of 12 quarterly surveys from August 2014 to May 2017 at a dam lake in the Fukushima nuclear disaster area, and variations of dissolved form of $$^{137}$$Cs and planktonic $$^{137}$$Cs were observed. Seasonal variations in dissolved $$^{137}$$Cs concentration with high in summer and low in winter were observed in the upstream, midstream and downstream areas of the lake, but no seasonal or site specific differences in planktonic $$^{137}$$Cs concentrations and dominant species were found. The amount of planktonic form of $$^{137}$$Cs in the water was less than 1.4% of the total $$^{137}$$Cs in the lake water, therefore the effect of plankton on the dynamics of $$^{137}$$Cs in the lake was minimal.

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

Radiation monitoring and evaluation of exposure doses to lift the evacuation orders for the zones designated for reconstruction and recovery

Sanada, Yukihisa; Kurikami, Hiroshi; Funaki, Hironori; Yoshimura, Kazuya; Abe, Tomohisa; Ishida, Mutsushi*; Tanimori, Soichiro*; Sato, Rina

Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(2), p.62 - 73, 2021/06

Japanese government starts to consider radiation protection in the "specific reconstruction reproduction base area" of which evacuation order will be lifted by 2023. It is essential to grab the present situations of radiation contamination and evaluate exposure dose in the area to realize the plan. Many surveys have evaluated the distributions of air dose rate and exposure dose has been estimated based on the results since the Fukushima Daiichi Nuclear Power Plant accident. Nevertheless, more detailed information on exposure is needed for the areas because its radiation level is relatively high. That is also to help make prudent evaluation plan. This study aimed to evaluate the detailed contamination situation there and estimate exposure dose with considering areal circumstances. Investigations were carried out for (1) airborne survey of air dose rate using an unmanned helicopter (2) evaluation of airborne radiocesium and (3) estimation of external/internal effective doses for typical activity patterns assumed.

Journal Articles

Evaluation of bioavailable radiocesium in the sediment in forest river and dam reservoir

Takechi, Seiichi*; Tsuji, Hideki*; Koshikawa, Masami*; Ito, Shoko*; Funaki, Hironori; Hayashi, Seiji*

Rikusuigaku Zasshi, 82(1), p.1 - 16, 2021/02

Since the Fukushima Daiichi Nuclear Power Plant accident in 2011, soil minerals and organic matter including radiocesium have been deposited in the dam lakes near the nuclear power plant. There is concern that radiocesium will gradually leach from the lake bottom into the lake water, resulting in prolonged radioactive contamination of the freshwater ecosystems especially in downstream of the dams. In this study, we collected undisturbed sediment core samples at the center of the Yokokawa Dam lake in Fukushima Prefecture and suspended sediment in the inflowing river of the dam for 4 years and evaluated the amount of bioavailable form of radiocesium (exchanged, oxidized, and organic forms) in these samples by sequential extraction tests using the BCR method focusing on the temporal change.

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.

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.

JAEA Reports

Applied research for the establishment of radiation monitoring and evaluation of exposure dose of residence at the zone designated for reconstruction and recovery

Funaki, Hironori; Takahara, Shogo; Sasaki, Miyuki; Yoshimura, Kazuya; Nakama, Shigeo; Sanada, Yukihisa

JAEA-Research 2018-016, 48 Pages, 2019/03

JAEA-Research-2018-016.pdf:29.73MB

Cabinet Office Nuclear Emergency Response Headquarters starts to consider radiation protection in the "specific reconstruction reproduction base area" of which evacuation order will be lifted by 2023. It is essential to grab the present situations of radiation contamination and evaluate exposure dose in the area to realize the plan. Many surveys have evaluated the distributions of air dose rate and exposure dose has been estimated based on the results since the Fukushima Daiichi Nuclear Power Plant accident. Nevertheless, more detailed information on exposure is needed for the areas because its radiation level is relatively high. That is also to help make prudent evaluation plan. This study aimed to evaluate the detailed contamination situation there and estimate exposure dose with considering areal circumstances. Investigations were carried out for (1) airborne survey of air dose rate using an unmanned helicopter (2) evaluation of airborne radiocesium and (3) estimation of external/internal effective doses for typical activity patterns assumed. Additionally, we applied new methods for the airborne survey to evaluate exposure dose. Our study showed a detailed three-dimensional map of air dose rate and clarified the distribution pattern in the areas. Results of effective dose estimation suggested that the internal effective dose due to inhalation accounts for less than 1% of the external effective dose.

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

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.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima; As a part of dissemination of evidence-based information

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

JAEA-Review-2017-018.pdf:17.58MB

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.

Journal Articles

Numerical study of sediment and $$^{137}$$Cs discharge out of reservoirs during various scale rainfall events

Kurikami, Hiroshi; Funaki, Hironori; Malins, A.; Kitamura, Akihiro; Onishi, Yasuo*

Journal of Environmental Radioactivity, 164, p.73 - 83, 2016/11

AA2015-0827.pdf:2.61MB

 Times Cited Count:12 Percentile:46.45(Environmental Sciences)

We performed simulations using the three-dimensional finite volume code FLESCOT to understand sediment and radiocesium transport in generic models of reservoirs with parameters similar to those in Fukushima Prefecture. The simulations model turbulent water flows, transport of sediments with different grain sizes, and radiocesium migration both in dissolved and particulate forms. To demonstrate the validity of the modeling approach for the Fukushima environment, we performed a test simulation of the Ogaki Dam reservoir over a typhoon. We simulated a set of generic model reservoirs systematically varying features such as flood intensity, reservoir volume and the radiocesium distribution coefficient. The results ascertain how these features affect the amount of sediment or $$^{137}$$Cs discharge downstream from the reservoirs, and the forms in which $$^{137}$$Cs is discharged. Silt carries the majority of the radiocesium in the larger flood events, while the clay-sorbed followed by dissolved forms are dominant in smaller events. The results can be used to derive indicative values of discharges from Fukushima reservoirs under arbitrary flood events.

Journal Articles

Fate of radiocesium in freshwater aquatic plants and algae in the vicinity of the Fukushima Daiichi Nuclear Power Plant

Sasaki, Yoshito; Funaki, Hironori; Iri, Shatei; Dohi, Terumi; Hagiwara, Hiroki

Limnology, 17(2), p.111 - 116, 2016/04

AA2015-0204.pdf:3.47MB

 Times Cited Count:7 Percentile:39(Limnology)

The behavior of radiocesium ($$^{137}$$Cs) in aquatic plants (five species) and algae (three genera) that had been grown in a river (one sampling point) and ponds (four sampling points) in the area around the Fukushima Daiichi Nuclear Power Plant was investigated. The sediment-to-plant transfer factor (TF) was measured. For aquatic plants, the highest value was 5.55 for ${it P. crispus}$ from the river; the lowest was 3.34 $$times$$ 10$$^{-2}$$ for ${it P. distinctus}$ from a pond. There were significant differences in the values for aquatic plants belonging to the same genus. The water-to-plant TF of filamentous algae (${it Spirogyra}$ sp.) and cyanobacteria (coexisting ${it Anabaena}$ sp. and ${it Microcystis}$ sp.) were 2.39 $$times$$ 10$$^{3}$$ and 1.26 $$times$$ 10$$^{3}$$, respectively. The $$^{137}$$Cs concentration of cyanobacteria fraction in pond water was 4.87 $$times$$ 10$$^{-1}$$ Bq/L, the same order of magnitude as the $$^{137}$$Cs concentration of pond water. Enrichment of radiocesium in cyanobacteria was not observed.

Journal Articles

The Behaviour of radiocaesium deposited in an upland reservoir after the Fukushima Nuclear Power Plant accident

Funaki, Hironori; Hagiwara, Hiroki; Tsuruta, Tadahiko

Materials Research Society Symposium Proceedings, Vol.1665, p.165 - 170, 2014/09

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