Confirmation of the sustainability of decontamination effects in public facilities and prediction of future air dose rates

Kusakabe, Kazuaki*; Watanabe, Masanori; Nishiuchi, Masashi*; Yamasaki, Takuhei*; Inoue, Hiromi*

Kankyo Hoshano Josen Gakkai-Shi, 11(1), p.15 - 23, 2023/03

The spread of radioactive materials caused by the Fukushima Daiichi Nuclear Power Plant accident that occurred in March 2011 contaminated a wide area that includes Fukushima Prefecture. Although air dose rates in Fukushima Prefecture have been steadily decreasing because of decontamination and the physical decay of radioactive materials, it is important to confirm the sustainability of decontamination effects in living areas and to predict future trends in air dose rates to reassure residents who are concerned regarding radiation exposure. This report aims to confirm the sustainability of the decontamination effects in public facilities after decontamination on a continuous and detailed basis, and to verify whether the future transition in air dose rates can be predicted using existing model. The air dose rates in public facilities after decontamination were measured via fixed-point and walking surveys, and the changes in air dose rates were clarified quantitatively for each facility. The measured values were compared with values obtained using existing model, and prediction accuracy was considered. The results showed that there was no evident recontamination after decontamination at any of the surveyed facilities, indicating that the decontamination effects were sustained. It was also confirmed that future trends in air dose rates at the facilities after decontamination could be accurately predicted by existing model. Key words: air dose rate, decontamination, future prediction, public facilities.

Examples of practical activities related to public understanding of radiation risk following the Fukushima nuclear accident

Naito, Wataru*; Uesaka, Motoki*; Kuroda, Yujiro*; Kono, Takahiko; Sakoda, Akihiro; Yoshida, Hiroko*

Radioprotection, 55(4), p.297 - 307, 2020/10

https://doi.org/10.1051/radiopro/2020086

After the Fukushima nuclear accident in Japan, a number of practical activities related to public understanding (PU) of radiation risks were implemented inside and outside Fukushima Prefecture. The various noteworthy approaches and strategies behind those practical activities have not been organized and made explicit thus far. In this study, we have organized the noteworthy practical activities related to PU of radiation risks following the Fukushima nuclear accident, and discussed them mainly from the standpoints of communication strategies and approaches. As several examples demonstrate, efforts to contextualize and localize radiation risk in various forms were observed during post-accident recovery in Fukushima, and these efforts were confirmed, through actual experiences, to be an important component of effective PU activities of radiation risks. Community-based or citizen science approaches, such as having affected residents or citizens to measure radioactivity, have contributed to the PU of radiological situations, but some challenges, such as ethical aspects and the handling of uncertainty, have also been revealed. In the era of information and communications technology, a number of citizens, experts, and agencies have made social media a popular platform for disseminating radiation risk messages to the public and have demonstrated that social media can play an important role in providing radiological risk information. The knowledge and lessons learned from the practical activities discussed in this study can be useful in enhancing PU of risks not only radiation but also other stressors such as toxic chemicals, preparing future disasters and supporting risk communication plans during recovery periods after disasters.

Confirmation of effect sustainability after decontamination and prediction of future air dose rate change

Nishiuchi, Masashi*; Suzuki, Satoshi*; Kawase, Keiichi; Watanabe, Masanori; Yamashita, Takuya

no journal, , 

By monitoring air dose rate etc. for public facilities where decontamination work was completed, we confirmed the status of maintaining decontamination effect, and predicted future air dose rate change by "The Restoration Support System for Environment (RESET)" and "prediction model of ambient dose equivalent rate" developed by JAEA. As a result, it became clear that the decontamination effect was maintained, and the future air dose rate was predicted to be reduced by about 30% after 10 years. This survey was conducted in response to concerns of municipalities. The research results were reported to the relevant municipalities and was used as the basic data residents correspondence etc. in the municipalities.

Radiocaesium dynamics in forested watersheds in Fukushima Prefecture

Taniguchi, Keisuke*; Takeuchi, Yukio*; Fujita, Kazuki*; Dohi, Terumi; Hayashi, Seiji*; Kuramoto, Takayuki*; Nomura, Naoki*; Aono, Tatsuo*

no journal, , 

In Fukushima Prefecture, although decontamination has been completed except for difficult-to-return areas, most of the forest has not been decontaminated yet. From the forest, radiocaesium may enter rivers and affect downstream areas. A survey was conducted in three forested watersheds of the Nanokazawa, Saruta, Nuno rivers located in Fukushima Prefecture to understand the amount and characteristics of radiocaesium flowing out. In each watershed, suspended solids (SS) were collected by a suspended sand sampler, water was collected every few months, and the water level and flow rate were measured. After freeze-drying the SS sample, the concentration of suspended Cs-137 was measured by a germanium semiconductor detector. The water sample was filtered through a membrane filter with a pore size of 0.45 m, then the dissolved Cs-137 was collected by the solid-phase extraction disk method or AMP coprecipitation method, and the dissolved Cs-137 concentration was measured by a germanium semiconductor detector. The ranges of dissolved Cs-137 concentration in FY2019 were 69-190 mBq/L in the Saruta River, 9.7-16 mBq/L in the Nanokazawa river, and ND-3.2 mBq/L in the Nuno River. In the poster, we will also present the results of SS measurements and flow observations.

Survey of activities of some Japanese academic societies toward the public before and after the Fukushima nuclear accident

Sakoda, Akihiro; Nomura, Naoki*; Naito, Wataru*; Kono, Takahiko; Kuroda, Yujiro*; Yoshida, Hiroko*

no journal, , 

The present study focused on radiation- or risk-associated academic societies in Japan, and collected data on experts' communication activities with the public and socially conscious activities within the societies to discuss how such experts should be in society.

Contribution of particulate Cs from rivers to Cs concentrations in coastal sediment off Fukushima

Suzuki, Shotaro*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Matsumoto, Akira*; Amano, Yosuke*; Enomoto, Masahiro*; Morioka, Yoshiaki*; Kamiyama, Kyoichi*; Takata, Hyoe*

no journal, ,