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.
Liu, X.; Machida, Masahiko; Kurikami, Hiroshi; Kitamura, Akihiro
Journal of Environmental Radioactivity, 203, p.135 - 146, 2019/07
In order to simulate the long-term migration and distribution of radiocesium after the Fukushima accident, a numerical model, Soil and Cesium Transport (SACT) based on universal soil loss equation (USLE), has been developed in previous studies. Although the SACT model's results on radiocesium discharge in 2011 are in reasonable agreement with field measurements, it fails to capture the sharp decrease of radiocesium flux in subsequent years, especially in the case of Abukuma River. We therefore have improved SACT by implementing the vertical migration and fixation of radiocesium in soil. For validation purpose, the annual average radiocesium concentration in sediments discharged from Abukuma River has been evaluated from measurement data. New model achieved much better agreement with the measurement results without parameter tuning.
Malins, A.; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko
Remediation Measures for Radioactively Contaminated Areas, p.259 - 272, 2019/00
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.
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 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 Cs and 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.
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
A study is presented on the applicability of the distribution coefficient () absorption/desorption model to simulate dissolved 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 Cs concentrations under both ambient and high flow conditions. By contrast the measured concentrations of dissolved Cs in the river water were much harder to reproduce with the simulations. By tuning the values for large particles, it was possible to reproduce the mean dissolved 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 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.
Saito, Hiroshi; Nozawa, Takashi; Takemiya, Hiroshi; Seki, Akiyuki; Matsubara, Takeshi; Saito, Kimiaki; Kitamura, Akihiro
JAEA-Review 2017-040, 34 Pages, 2018/03
The accidents at Fukushima Daiichi Nuclear Power Station on March 11th 2011, released significant amount of radionuclide to the environment. It has migrated to the human habitation and raised concerns of possible effect on human health, and for that a lot of researches have been performed. JAEA created and opened "Database for Radioactive Substance Monitoring Data" for usage of obtained data. For accurate modelling and future forecast using numerical code and the data, "Supporting Environment for Processing Simulation Codes" has been operated. In addition, research results have been opened as Q&A style "Knowledge Base for Environmental Remediation" in JAEA's website. The "Comprehensive Evaluation System" composed of these components, should act more interrelated and integrated as one system. Besides, information dissemination is not enough to the outside. The report summarizes the current status, remaining issues and expected improvement of each component and the system.
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.
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.
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
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 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 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.
Kurikami, Hiroshi; Niizato, Tadafumi; Tsuruta, Tadahiko; Kato, Tomoko; Kitamura, Akihiro; Kanno, Mitsuhiro*; Kurosawa, Naohiro*
JAEA-Research 2016-020, 50 Pages, 2017/01
In this report, we developed a compartment model of radionuclide migration in environment based on exposure pathways in a river basin scale and performed a preliminary calculation. The results showed good agreement with some measurement, although the comparison of bed sediment, transportation to outer sea and to agricultural products with the measurement was not enough. We continue to validate the model.
Saito, Hiroshi; Yamaguchi, Masaaki; Kitamura, Akihiro
JAEA-Testing 2016-003, 68 Pages, 2016/12
JAEA has developed a simple and fast simulation program "SACT" (Soil and Cesium Transport) to predict a long-term distribution of Cs deposited on the land surface due to the Fukushima Daiichi Nuclear Power Station accident. It calculates soil movement (erosion, transportation, deposition) and Cs migration, and predicts its future distribution with the assumption that it is adhered to soil. SACT uses USLE (Universal Soil Loss Equation) for potential soil loss and simple equations for soil transportation and deposition. The Cs amount is predicted by the amount of soil movement and Cs concentration ratio for each grain-size of soil. SACT is characterized by its simplicity which enables fast calculation for wide area for long-term duration using existing equations. Data for parameters are widely available and site-specific calculations are possible using data of the targeted area. This manual provides useful and necessary information to users and facilitates the use of SACT widely.
Kurikami, Hiroshi; Funaki, Hironori; Malins, A.; Kitamura, Akihiro; Onishi, Yasuo*
Journal of Environmental Radioactivity, 164, p.73 - 83, 2016/11
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 Cs discharge downstream from the reservoirs, and the forms in which 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.
Sakai, Akihiro; Kurosawa, Ryohei*; Nakata, Hisakazu; Okada, Shota; Izumo, Sari; Sato, Makoto*; Kitamura, Yoichi*; Honda, Yasutake*; Takaoka, Katsuki*; Amazawa, Hiroya
JAEA-Technology 2016-019, 134 Pages, 2016/10
Japan Atomic Energy Agency has been developing to design trench disposal facility with impermeable layers in order to dispose of miscellaneous waste. Geomembrane liners have a function that prevent seepage of leachant and collect the leachant. However, the geomembrane liners do not necessarily provide the expected performance due to damage generated when heavy equipment contacts with the liner. Therefore, we studied the impermeable layers having high performance of preventing seepage of leachant including radioactivity taking into account characteristics of low permeable materials and effect of multiple layer structure. As results, we have evaluated that the composite layers composed by a drainage layer, geomembrane liners and a low permeable layer are most effective structure to prevent seepage of leachant. Taking into account disposal of waste including cesium, we also considered zeolite containing sheets for adsorption of cesium were installed in the impermeable layers.
Malins, A.; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko
Health Physics, 111(4), p.357 - 366, 2016/10
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
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.
Malins, A.; Kurikami, Hiroshi; Nakama, Shigeo; Saito, Tatsuo; Okumura, Masahiko; Machida, Masahiko; Kitamura, Akihiro
Journal of Environmental Radioactivity, 151(Part 1), p.38 - 49, 2016/01
The air dose rate in an environment contaminated with Cs and Cs depends on the amount, depth profile and horizontal distribution of these contaminants within the ground. This paper introduces and verifies a tool that models these variables and calculates ambient dose equivalent rates at 1 m above the ground. Good correlation is found between predicted dose rates and dose rates measured with survey meters in Fukushima Prefecture in areas contaminated with radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. Better predictions are obtained by modeling the horizontal distribution of radioactive cesium across an area if multiple soil samples are available, as opposed to assuming a spatially homogeneous contamination distribution. Reductions seen in air dose rates above flat, undisturbed fields in Fukushima Prefecture are consistent with decrement by radioactive decay and downward migration of cesium into soil. Analysis of remediation strategies for farmland soils confirmed that topsoil removal and interchanging a topsoil layer with a subsoil layer result in similar reductions in the air dose rate.
Nuryanthi, N.*; Yamaki, Tetsuya; Kitamura, Akane; Koshikawa, Hiroshi; Yoshimura, Kimio; Sawada, Shinichi; Hasegawa, Shin; Asano, Masaharu; Maekawa, Yasunari; Suzuki, Akihiro*; et al.
Transactions of the Materials Research Society of Japan, 40(4), p.359 - 362, 2015/12
The ion-track grafting of a vinylbenzyl chloride (VBC) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film is necessary for preparing nanostructured hydroxide-ion-conductive electrolyte membranes. A key for success here is to obtain as high graft levels as possible (for higher conductivity) in a smaller number of tracks (for improving the other membrane properties). To this end, therefore, the effect of the medium for the VBC grafting was investigated as part of our continuing effort to optimize the experimental conditions. A 25 m-thick ETFE film was irradiated in a vacuum chamber with 560 MeV Xe at different fluences, and then the grafting was performed by immersing the irradiated films in a 20vol% VBC monomer at 60C. A medium was a mixture of water (HO) and isopropyl alcohol (iPrOH) at different volume ratios. The degree of grafting increased as the HO content became higher, and reached a maximum in pure HO. These results can be explained by considering the well-known Trommsdorff effect, in which poor solubility of the grafted polymer in polar media leads to an increased polymerization rate probably due to a lower termination rate.
Kurikami, Hiroshi; Kitamura, Akihiro; Yamada, Susumu; Machida, Masahiko
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05
Several numerical models have been prepared to deal with various time- and spatial-scale issues related to radioactive cesium migration in environment in Fukushima area. This paper describes fragments of the JAEA's approaches of modeling to deal with the issues corresponding to radioactive cesium migration in environment with some case studies.
Yamada, Susumu; Kitamura, Akihiro; Kurikami, Hiroshi; Machida, Masahiko
Proceedings of Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015) (CD-ROM), 9 Pages, 2015/04
no abstracts in English