Yoshimura, Kazuya; Watanabe, Takayoshi; Kurikami, Hiroshi
Journal of Environmental Radioactivity, 217, p.106213_1 - 106213_6, 2020/06
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
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.
Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Sasaki, Yoshito; Niizato, Tadafumi
Journal of Environmental Radioactivity, 208-209, p.106005_1 - 106005_11, 2019/11
To assess the uptake of Cs-137 (Cs) by freshwater fish, we developed a compartment model for the migration of 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 Cs from forests to river water for the uptake of Cs by freshwater fish. The results suggest that the decreasing trend of 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 Cs concentrations within these forest compartments plateau at around ten years after the fallout due to Cs circulation in forests reaching an equilibrium state.
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).
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.
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.
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.
Takeishi, Minoru; Shibamichi, Masaru; Malins, A.; Kurikami, Hiroshi; Murakami, Mitsuhiro*; Saegusa, Jun; Yoneya, Masayuki
Journal of Environmental Radioactivity, 177, p.1 - 12, 2017/10
By convention radiation measurements from vehicle-borne surveys are converted to the dose rate at 1 m above the ground in the absence of the vehicle. To improve the accuracy of the converted results from vehicle-borne surveys, we investigated combining measurements from two detectors mounted on the vehicle at different heights above the ground. A dual-detector setup was added to a JAEA monitoring car and compared against hand-held survey meter measurements in Fukushima Prefecture. The dose rates obtained by combining measurements from two detectors were within 20% of the hand-held reference measurements. The combined results from the two detectors were more accurate than those from either the roof-mounted detector, or the detector inside the vehicle, taken alone. When radiocesium is deficient on a road compared to the adjacent land, mounting detectors high on vehicles yields dose rates closer to the values adjacent to the road. We also investigated mounting heights for vehicle-borne detectors using Monte Carlo -ray simulations.
Kurikami, Hiroshi; Malins, A.; Takeishi, Minoru; Saito, Kimiaki; Iijima, Kazuki
Journal of Environmental Radioactivity, 171, p.99 - 109, 2017/05
A modified diffusion-sorption-fixation model (mDSF) is proposed to describe the vertical migration of radiocesium in soils following fallout. The model introduces kinetics for reversible sites, meaning that the exponential-shape radiocesium distribution can be reproduced immediately following fallout. The initial relaxation mass depth of the distribution is determined by the diffusion length, which depends on the distribution coefficient, sorption rate and dispersion coefficient. The model captures the long tails of the radiocesium distribution at large depths. These tails are caused by different rates for kinetic sorption and desorption.
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.
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.
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.
Saegusa, Jun; Tagawa, Akihiro; Kurikami, Hiroshi; Iijima, Kazuki; Yoshikawa, Hideki; Tokizawa, Takayuki; Nakayama, Shinichi; Ishida, Junichiro
Mechanical Engineering Journal (Internet), 3(3), p.15-00609_1 - 15-00609_7, 2016/06
After the Fukushima nuclear accident, JAEA lead off demonstration tests to find out effective decontamination methods for various school facilities in Fukushima. It included (1) dose reduction measures at schoolyards, (2) purification of swimming pool water and (3) removal of surface contamination of playground equipments. Through these tests, they established practical methods suitable for each situation; (1) At school yards, dose rates were drastically reduced by removing topsoil which was then placed in trenches of 1 m deep; (2) For the purification of pool water, the flocculation-coagulation treatment was found to be effective for collecting radiocesium dissolved in the water; (3) Demonstration tests for playground equipments, such as horizontal bars and a sandbox wood frame, suggested that effectiveness of decontamination considerably varied depending on the material, paint or coating condition. This paper reviews these demonstrations.
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.