• Journal of Radiation Protection and Research
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• v.42 no.3
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• pp.166-175
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• 2017

Background: This study presents food ingestion standards for radioactivity that can be applied in nuclear emergency exposure situations, and discusses the validity of the current domestic standards. Materials and Methods: This study derived food ingestion standards for radiocesium and radioiodine using domestic food intake rates and intervention levels, which serve as a basis for determining the necessity of public protective actions, and then compared them with the existing guidelines. Operational intervention levels were also derived using domestic food intake rates, and were compared with those of the International Atomic Energy Agency. Results and Discussion: The derived activity concentrations for food ingestion standards of radiocesium for infants were higher than those in the Act on Physical Protection and Radiological Emergency (APPRE) for all food categories, while for adults, the derived activity concentrations for drinking water and milk appeared to be slightly lower. The derived activity concentrations for vegetables, fruits, and grains were greater than those in the guidelines of the APPRE, while the derived activity concentrations for meat and seafood were similar to those in the APPRE. The derived activity concentrations for radioiodine were greater than both domestic and global standards. The calculated operational intervention levels (OILs) based on domestic food intake rates were greater than the IAEA's default OIL6 values for most radionuclides, except for a few ${\alpha}$-radionuclides. Conclusion: The current domestic guidelines turned out to be conservative overall, compared to the present results that were calculated using domestic food intake rates. It is recommended that the domestic guidelines should be revised and complemented transparently through an in-depth review by stakeholders on a solid scientific basis.

• Journal of Radiation Protection and Research
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• v.46 no.4
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• pp.184-193
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• 2021

Background: The radionuclides released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident 9 years ago are still being monitored by various research teams and the Japanese government. Comparison of different surveys' results could help evaluate the exposure doses and the mechanism of radiocesium behavior in the urban environment in the area. In this study, we clarified the relationship between land use and temporal changes in the ambient dose rates (air dose rates) using big data. Materials and Methods: We set a series of 1 × 1 km² meshes within the 80 km zone of the FDNPP to compare the different survey results. We then prepared an analysis dataset from all survey meshes to analyze the temporal change in the air dose rate. The selected meshes included data from all survey types (airborne, fixed point, backpack, and carborne) obtained through the all-time survey campaigns. Results and Discussion: The characteristics of each survey's results were then evaluated using this dataset, as they depended on the measurement object. The dataset analysis revealed that, for example, the results of the carborne survey were smaller than those of the other surveys because the field of view of the carborne survey was limited to paved roads. The location factor of different land uses was also evaluated considering the characteristics of the four survey methods. Nine years after the FDNPP accident, the location factor ranged from 0.26 to 0.49, while the half-life of the air dose rate ranged from 1.2 to 1.6. Conclusion: We found that the decreasing trend in the air dose rate of the FDNPP accident was similar to the results obtained after the Chernobyl accident. These parameters will be useful for the prediction of the future exposure dose at the post-accident.

• Mycobiology
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• v.45 no.1
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• pp.15-19
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• 2017

This study proposed a rapid method to quantify the colonization rate of arbuscular mycorrhizal fungi (AMF) in plant roots. The method involved the use of an image analysis software (WinRHIZO Pro). The colonization rate is defined as the ratio of the fungal body to the plant root area in a micrograph. Three seedlings of Chengiopanax sciadophylloides, a woody species that accumulates radiocesium, were collected from a secondary forest in the Yamakiya district of Kawamata, Fukushima Prefecture during May-September 2014. The colonization of AMF structures was examined under a light microscope, and the percentage of colonization was determined using the WinRHIZO method. The superiority of the new method was verified by comparing with a modified grid-line intersect method. The colonization of AMF was confirmed in all the seedlings, and a significant coefficient of determination ($R^2=0.94$) was found with both the methods. The results suggested that the WinRHIZO method is reliable for estimating the colonization of AMF in C. sciadophylloides.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.1
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• pp.95-114
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• 2023

During the decades after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, ambient dose rates have markedly decreased when compared to those at the early state of the accident. Government projects have been continuously conducted by surveying the ambient dose rate and radiocesium distributions. Airborne surveys using crewed helicopters and unmanned aerial vehicles (UAVs) are the best methods for obtaining an overall picture of the distribution. However, ground-based surveys are required for accurate measurements near the population. The differences between these methods include the knowledge of the post depositional behavior of radionuclides in land use. The survey results form the basis for policy decisions such as lifting evacuation zones, decontamination, and other countermeasures. These surveys contain crucial findings regarding post-accident responses. This paper reviews the survey methods of government projects and current situation around the FDNPS. The visualization methods and databases of ambient dose rates are also reviewed to provide information to the population.

• Journal of Korean Society on Water Environment
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• v.38 no.1
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• pp.10-18
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• 2022

This study was conducted to investigate the effect of soil and groundwater environment changed by wildfire on cesium adsorption and transport. Soil samples (A, B) used in the study were collected from Gangwon-do, where wildfires frequently occur, and the adsorption and transport of cesium in the samples were evaluated through batch and column experiments. As a result of the batch adsorption experiments with various concentrations of cesium (C_W ≈ 10~10⁵ ㎍/L), the adsorption distribution coefficient (K_d) of cesium was higher in sample A for all observed concentrations. It means that the adsorption capacity of sample A was higher to that of sample B, which was also confirmed through the parameters of adsorption isotherm models (Freundlich and Langmuir model) applied to the experimental results. The fixed bed column experiments simulated the actual soil and groundwater environment, and they showed that cesium was retarded approximately 43 and 27 times than a nonreactive tracer in sample A and B, respectively. In particular, a significant retardation occurred in the sample A. Although sample A contains little clays, total organic carbon (TOC) contents were 3 times greater than sample B. These results imply that particulate organic matter caused by wildfire might influence the adsorption and transport of cesium in the organic matter-rich soil and groundwater environment.

• Journal of Radiation Protection and Research
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• v.47 no.1
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• pp.30-38
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• 2022

Background: Residential areas have some factors on the external exposure of residents, who usually spend a long time in these areas. Although various survey has been carried out by the government or the research institutions after the Fukushima Daiichi Nuclear Power Plant accident, the mechanism of radiocesium inventory in the terrestrial zone has not been cleared. To better evaluate the radiation environment, this study investigated the temporal changes in air dose rate and ¹³⁷Cs inventories (Bq/m²) in residential areas and agricultural fields. Materials and Methods: Air dose rate and ¹³⁷Cs inventories were investigated in residential areas located in an evacuation zone at 5-8 km from the Fukushima Daiichi Nuclear Power Plant. From December 2014 to September 2018, the air dose rate distribution was investigated through a walking survey (backpack survey), which was conducted by operators carrying a γ-ray detector on their backs. Additionally, from December 2014 to January 2021, the ¹³⁷Cs inventories on paved and permeable grounds were also measured using a portable γ-ray detector. Results and Discussion: In the areas where decontamination was not performed, the air dose rate decreased faster in residential areas than in agricultural fields. Moreover, the ¹³⁷Cs inventory on paved surfaces decreased with time owing to the horizontal wash-off, while the ¹³⁷Cs inventory on permeable surfaces decreased dramatically owing to the decontamination activities. Conclusion: These findings suggest that the horizontal wash-off of ¹³⁷Cs on paved surfaces facilitated the air dose rate decrease in residential areas to a greater extent compared with agricultural fields, in which the air dose rate decreased because of the vertical migration of ¹³⁷Cs. Results of this study can explain the faster environmental restoration in a residential environment reported by previous studies.

• Nuclear Engineering and Technology
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• v.10 no.3
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• pp.153-163
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• 1978

The problems of solid waste disposal into the ground in connection with environmental aspects in the vicinity of a site would be very significant, though ground disposal for solid waste is safe and economical method. Studies of the waste-movement and migration of radionuclides (Sr-90 and Cs-137) for the disposal into the ground were performed under laboratory and field conditions. Affinity of the soils for radionuclide solution was higher than that in the acid solution. The sorption of radionuclides by the soils showed a time-dependent reation. The migration rates of radiostrontium and radiocesium were a range of 3.73$\times$10$^{-3}$ to 10.9$\times$10$^{-3}$ cm/day. The nuclides in the soil migrate much more slowly than the water, probably due to its high exchange capacity. The observed distribution of tritium was compared with that calculated by a mathematical model based on diffusivity. This study suggests that the tritiated water can be used to trace the movement of ground water.

• Korean Journal of Environmental Agriculture
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• v.2 no.1
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• pp.30-34
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• 1983

The present study was carried out to determine the effect of a radionuclide, cesium-137, in soybean, which is an element released usually from nuclear facilities. Soybean plants were grown on the pots treated with cesium-137 $0.5{\sim}60{\mu}Ci/1kg$ soil and the uptake, translocation and accumulation of the radiocesium in the plant parts were measured at different growth stage. The results are summarized as follows: 1) Visual toxic symptoms on the plants due to treatment of radioactive cesium were not observed up to $60{\mu}Ci/10Kg$ soil in a pot. 2) The uptake of cesium-137 in soybean plant was increased with increment of concentration applied, while the uptake of potassium was proportionally decreased, indicating to have an ion antagonistic relationship between them. 3) The absolute amounts of cesium-137 in the plants were gradually increased by the pod setting stage, but rather reduced at harvesting stage. The accumulation occurred more in the leaves and stems than the soybean seeds. 4) The rate of uptake was ranged from 0.069 to 0.005 with proportional decrease by increasing concentration applied and the rate of Cs-137 translocation from plants to seeds was averaged 38.6% in soybean plant. The concentration coefficient was 0.04 in the soybean seeds from the pots treated with $20{\mu}Ci$ of cesium-137 and decreased with increment of cesium-137 applied.