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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:0

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


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


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


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:5 Percentile:59.32(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:5 Percentile:51.46(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:6 Percentile:44.83(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


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


 Times Cited Count:9 Percentile:55.26(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


 Times Cited Count:5 Percentile:64.16(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

Journal Articles

Distribution of radioactive cesium in trees and effect of decontamination of forest contaminated by the Fukushima nuclear accident

Iijima, Kazuki; Funaki, Hironori; Tokizawa, Takayuki; Nakayama, Shinichi

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 6 Pages, 2013/09

In decontamination pilot projects conducted by Japan Atomic Energy Agency (JAEA), many different techniques were tested to determine their applicability to remediate areas evacuated after the Fukushima Daiichi nuclear accident. The projects evaluated the radioactive contamination of trees and the effectiveness of decontaminating a highly contaminated evergreen forest. As the first step, three Japanese cedar trees and three fir trees were cut down and the distributions of radioactive cesium (Cs) were measured in each. The total concentrations of $$^{134}$$Cs and $$^{137}$$Cs in the leaves and branches were about 1 MBq/kg for both cedar and fir trees, and were appreciably higher than in the bark for cedar. The concentrations in the outer part of the trunks (under the bark) were lower, on the order of 10 kBq/kg, and those in the core of the trunks were lower than 1 kBq/kg for both kinds of trees. The observation that the Cs concentrations are higher in the outer part of trees, is compatible with the assumption that radio-Cs was mostly adsorbed on the surface of trees and partly penetrated into the trunks through the bark. Evolution of air dose rates in a 100$$times$$60 m pasture adjacent to the forest was monitored during decontamination of the forest and of the pasture itself. The dose rates in the pasture decreased drastically after stripping contaminated topsoil from the pasture and decreased slightly more after stripping contaminated topsoil of the forest floor and pruning the trees. Cutting down and removing 84 trees in the outermost area (10-m width) of the forest also slightly decreased these dose rates. After decontamination, the residual dose rates around the highly contaminated forest were mostly attributed to radioactive Cs existing in or on trees and topsoil in the untouched forest beyond the decontaminated area.

Journal Articles

Decontamination of outdoor school swimming pools in Fukushima after the nuclear accident in March 2011

Saegusa, Jun; Kurikami, Hiroshi; Yasuda, Ryo; Kurihara, Kazuo; Arai, Shigeki; Kuroki, Ryota; Matsuhashi, Shimpei; Ozawa, Takashi; Goto, Hiroaki; Takano, Takao; et al.

Health Physics, 104(3), p.243 - 250, 2013/03

 Times Cited Count:3 Percentile:67.8(Environmental Sciences)

After the Nuclear accident on March 2011, water discharge from many outdoor swimming pools in the Fukushima prefecture was suspended out of concern that radiocesium in the pool water would flow into farmlands. We have reviewed the existing flocculation method for decontaminating pool water and established a practical decontamination method by demonstrating the process at several pools in the Fukushima prefecture.

Journal Articles

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

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

Nippon Genshiryoku Gakkai Wabun Rombunshi, 12(1), p.1 - 12, 2013/03

Since the Fukushima Daiichi Nuclear Power Plant accident caused by the Tohoku Region Pacific Coast Earthquake, decontamination work has been conducted. Decontamination wastes including removed soil, grass and trees are to be stored safely at temporary storage facilities for up to three 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. Temporary storage facilities of different technical specifications were designed and constructed under various topographic conditions and land-use. In order to support designing, constructing and monitoring of temporary storage facilities for decontamination wastes during the full-scale decontamination, technical know-how obtained during the decontamination pilot project has been identified and summarized in this paper.

Journal Articles

Molecular and carbon isotope compositions of hydrocarbon gas in Neogene sedimentary rocks in Horonobe area, northern Hokkaido, Japan

Funaki, Hironori; Ishiyama, Koji*; Waseda, Amane*; Kato, Susumu*; Watanabe, Kunio*

Chigaku Zasshi, 121(6), p.929 - 945, 2012/12

Molecular and carbon isotope compositions of hydrocarbon gas have information related to their generation, migration and accumulation, and serve evaluations of gas permeability in sedimentary rocks. We conducted headspace gas analysis at the cores (below 500 m depth) to evaluate gas permeability in Neogene sedimentary rocks in the Horonobe, Hokkaido, Japan. As a result, it was shown that hydrocarbon gases were almost biogenic methane. Further analysis of these data indicated that concentration and carbon isotope of methane varied carbon isotopic fractionation during anaerobic microbial oxidation and migration near the faults. A formation of high concentration and light carbon isotope of methane at present in the study area is low gas permeability and is less affected by secondary post-generic process.

Journal Articles

The Relationships among brittleness, deformation behavior, and transport properties in mudstones; An Example from the Horonobe Underground Research Laboratory, Japan

Ishii, Eiichi; Sanada, Hiroyuki; Funaki, Hironori; Sugita, Yutaka; Kurikami, Hiroshi

Journal of Geophysical Research; Solid Earth, 116(B09), p.B09206_1 - B09206_15, 2011/10

 Times Cited Count:23 Percentile:35.43(Geochemistry & Geophysics)

This paper addresses relationship among brittleness, deformation behavior, and transport properties of mudstones at the Horonobe Underground Research Laboratory site, Japan. The mudstones include indurated/cemented rocks by silica diagenesis. The geological, mechanical and hydrogeological data were systematically interpreted using a brittleness index (BRI) concept which is defined using unconfined compressive strength and the unconfined compressive strength of a normally consolidated rock in non-overpressured domains.

Journal Articles

Influence of a fault system on rock mass response to shaft excavation in soft sedimentary rock, Horonobe area, northern Japan

Tokiwa, Tetsuya; Tsusaka, Kimikazu; Ishii, Eiichi; Sanada, Hiroyuki; Tominaga, Eiji*; Hatsuyama, Yoshihiro*; Funaki, Hironori

International Journal of Rock Mechanics and Mining Sciences, 48(5), p.773 - 781, 2011/07

 Times Cited Count:10 Percentile:28.74(Engineering, Geological)

This paper focuses attention on stress field that produced fault system, and presents an example of the relationship between fault system and rock mass response to shaft excavation in soft sedimentary rocks in the Horonobe area, Japan. The directions determined by fault-slip analysis are close to the direction of maximum and minimum diameter reduction in the shaft. The results show that fault system can affects rock mass response to shaft excavation in soft rock and furthermore, and it is considered that the rock mass deformation was controlled by fault system. In addition, it is likely that we can assess and predict rock mass behavior by focusing on palaeo-stress field that produced fault system.

Journal Articles

Relationship between fault growth mechanism and permeability variations with depth of siliceous mudstones in northern Hokkaido, Japan

Ishii, Eiichi; Funaki, Hironori; Tokiwa, Tetsuya; Ota, Kunio

Journal of Structural Geology, 32(11), p.1792 - 1805, 2010/11

 Times Cited Count:23 Percentile:37.81(Geosciences, Multidisciplinary)

In order to assess influences of a remote mean stress on a principal mode of failure near fault tips due to fault slip in a lithologically homogeneous, fractured rock mass, the growth mechanisms of strike-slip faults on outcrop-scale in the siliceous mudstones of northern Hokkaido, Japan, have been studied. A multifaceted approach combining geological characterizations of fractures, rock mechanical characterizations, and theoretical analyses have been done, which suggested (1) the principal mode of failure depend on not only the rock strengths, but also the remote mean stresses, (2) during and/or after uplift and erosion the faults grew mainly by linking with adjacent faults via many splay cracks which are formed by tensile failure above roughly 400 m depth, while, below the depth, the faults predominantly grew by shear failure. Such growth mechanisms are consistent with the fact that highly permeable sections are restricted to depths of less than 400 m.

JAEA Reports

Horonobe Underground Research Laboratory Project; The Results of the pilot borehole investigation of the ventilation shaft (PB-V01); Geophysical loggings

Funaki, Hironori; Asamori, Koichi; Sanada, Hiroyuki; Hatsuyama, Yoshihiro*; Yamamoto, Takuya*; Ijiri, Yuji*; Matsuoka, Kiyoyuki*; Kimura, Kazuhiro*; Lin, S.*; Kumagai, Toshifumi*

JAEA-Data/Code 2010-002, 151 Pages, 2010/06


JAEA is implementing Horonobe URL Project as research and development of geological disposal. The investigation of the pilot boring was carried out around the Ventilation shaft in order to decide grouting plan and plant of effluent treating. This report summarize as data-code results of geophysical loggings.

Journal Articles

Relationship between fault system estimated by the fault-striation analysis of drilling cores and rock mass behavior induced by shaft excavation in the Horonobe area, northern Japan

Tokiwa, Tetsuya; Ishii, Eiichi; Funaki, Hironori; Tsusaka, Kimikazu; Sanada, Hiroyuki

Proceedings of 3rd International Workshop and Conference on Earth Resources Technology 2009 (CD-ROM), p.159 - 168, 2009/12

Japan Atomic Energy Agency has been constructing underground facilities since 2005 in the Horonobe area. Before the construction, the rock stress was measured by the hydraulic fracturing method using boreholes. In this area, the result showed that the direction of the major horizontal principal stress was in E-W direction. On the other hand, in shaft excavation, the direction of the predominant diameter reduction was observed in NNE-SSW to NE-SW direction. The difference would be attributed to the fact that fault system in the rock affects the deformation of shaft. The authors applied fault-striation analysis with faults identified on drilling cores. The direction of the major principal stress estimated by fault-striation analysis approximately corresponds to the predominant directions of the deformation caused by the shaft excavation. The result shows that fault system affects rock mass behavior in shaft excavation.

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