Mineral composition characteristics of radiocesium sorbed and transported sediments within the Tomioka river basin in Fukushima Prefecture

Hagiwara, Hiroki; Konishi, Hiromi*; Nakanishi, Takahiro; Fujiwara, Kenso; Iijima, Kazuki; Kitamura, Akihiro

Journal of Environmental Radioactivity, 211, p.106042_1 - 106042_10, 2020/01

https://doi.org/10.1016/j.jenvrad.2019.106042

Temporal change in concentration of radiocesium in Fukushima river water

Nakanishi, Takahiro

Isotope News, (765), p.22 - 25, 2019/10

Temporal change in concentration of radiocesium in Fukushima river water are outlined. Radiocesium concentration in river water keeps decreasing after several years, however, the declining trend for the dissolved radiocesium concentration is gradually decreasing with time.

Temporal changes in radiocesium deposition on the Fukushima floodplain

Nakanishi, Takahiro; Sato, Seiji; Matsumoto, Takumi*

Radiation Protection Dosimetry, 184(3-4), p.311 - 314, 2019/10

https://doi.org/10.1093/rpd/ncz086

There has been significant concern about an increase of exposure dose in living sphere due to the accumulation of radiocesium discharged from contaminated mountainous forest in Fukushima. In this study, we investigated the history of radiocesium deposition on some floodplains in Fukushima. Radiocesium concentrations of river suspended particles and air dose rates at floodplains were also observed continuously. In many situations, annual sediment accumulation at floodplains was only several kg m and its radiocesium concentration was gradually decreasing in line with that of suspended particle. Simultaneously, air dose rates on floodplains were decreasing with time. In 2015 with heavy flood discharge, several hundred kg m of sediment accumulation and sharply decrease of air dose rate was observed at rivers without reservoir. Conversely, radiocesium accumulation at floodplain was significant reduced due to deposition on upstream reservoir.

Student and Young researcher's view of research on health physics and environment science

Miwa, Kazuji; Terasaka, Yuta; Ochi, Kotaro; Futemma, Akira; Sasaki, Miyuki; Hirouchi, Jun

Nippon Genshiryoku Gakkai-Shi, 61(9), p.687 - 691, 2019/09

This report summarizes the contents of the session of the Health Physics and Environment Science Division, which was held in Atomic Energy Society of Japan 2019 Spring Meeting. In this session, six students and young researchers who engaged in the field of nuclear energy and radiation gave a lecture about health physics and environmental science research through their expertise. After the all presentations end, we took discussion time about the issues and future development in this field with all attendees. In this report, we summarized each lecture outline and discussion contents.

Radiation monitoring using manned helicopter around the nuclear power station in the fiscal year 2017 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Ishizaki, Azusa; Iwai, Takeyuki*; Seguchi, Eisaku; Matsunaga, Yuki*; Kawabata, Tomoki; Toyoda, Masayuki*; Tobita, Shinichiro*; Hiraga, Shogo*; et al.

JAEA-Technology 2018-015, 120 Pages, 2019/02

JAEA-Technology-2018-015.pdf:15.01MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company (TEPCO), caused by the Great East Japan Earthquake and the following tsunami on March 11, 2011, a large amount of radioactive material was released from the NPS. After the nuclear disaster, airborne radiation monitoring using manned helicopter was conducted around FDNPS. The results in the fiscal 2017 were summarized in this report. In addition, we developed and systemized the discrimination technique of the Rn-progenies. The accuracy of aerial radiation monitoring was evaluated by taking into consideration GPS data error.

Development of an analytical method for estimating three-dimensional distribution of sediment-associated radiocesium at a reservoir bottom

Ochi, Kotaro; Urabe, Yoshimi*; Yamada, Tsutomu*; Sanada, Yukihisa

Analytical Chemistry, 90(18), p.10795 - 10802, 2018/09

https://doi.org/10.1021/acs.analchem.8b01746

After the Fukushima Daiichi Nuclear Power Station accident, the distributions of sediment-associated radiocesium have been investigated to evaluate the dispersion and accumulation of radiocesium in the reservoir field. To develop an analytical method for measuring the horizontal and vertical distributions of radiocesium on a wide scale, we obtained 253 -ray spectra using a NaI(Tl) scintillation detector at the bottom of 64 ponds in Fukushima during 2014-2016. The depth profile of sediment-associated radiocesium was found to be correlated with intensities of scattered and photo peaks. In parallel, core sediments were collected in same ponds to validate the estimates. Good agreement was observed between the results of in situ spectrometry and core sampling. These results indicated that our developed method would be a good approach for understanding the behavior of radiocesium and determining whether decontamination of reservoirs is required.

Evaluation of physicochemical properties of radioactive cesium in municipal solid waste incineration fly ash by particle size classification and leaching tests

Fujii, Kengo*; Ochi, Kotaro; Obuchi, Atsushi*; Koike, Yuya*

Journal of Environmental Management, 217, p.157 - 163, 2018/07

https://doi.org/10.1016/j.jenvman.2018.03.028

After the Fukushima Daiichi-Nuclear Power Plant accident, environmental recovery was a major issue because a considerable amount of municipal solid waste incineration (MSWI) fly ash was highly contaminated with radioactive cesium. In this study, MSWI fly ash was sampled in Fukushima Prefecture, and the physicochemical properties of radioactive cesium in MSWI fly ash were evaluated by particle size classification and the Japanese leaching test No. 13 (JLT-13). The results obtained from the classification of fly ash indicated that the activity concentration of radioactive cesium and the content of the coexisting matter (i.e., chloride, potassium, and sylvite) temporarily change in response to the particle size of fly ash. X-ray diffraction results indicated that water-soluble radioactive cesium exists as CsCl because of the cooling process and that insoluble cesium is bound to the inner sphere of amorphous matter.

Factors controlling Cs activity concentrations in sediment collected off the coast of Fukushima Prefecture in 2013-2015

Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Ishimaru, Takashi*; Kanda, Jota*; Nishikawa, Jun*; Otosaka, Shigeyoshi

Geochemical Journal, 52(2), p.201 - 209, 2018/00

https://doi.org/10.2343/geochemj.2.0504

To elucidate recent activity levels and the behavior of radiocesium in the coast off Fukushima Prefecture, lateral and vertical distributions of Cs in sediment were observed in 2013-2015 at 12 monitoring stations. At stations around the water depth of 100 m, relatively higher Cs activities were observed from surface sedimentary layer (0-3 cm). In these stations, sediments had high content of silt to clay particles and organic matter. The high Cs activities in the surface sediments were attributed to accumulation of highly mobile sediment particles. In October 2014, at some coastal stations, sharp peaks of Cs activities were observed in the subsurface (5-16 cm) sediments, whereas such broad peaks were not found in October 2015. These results suggest that the Cs activities in sediment had largely changed by lateral transport and re-sedimentation on the surface, as well as sediment mixing in the middle-layers.

Reply to "Comments on radiation-damage resistance in phyllosilicate minerals from first principles and implications for radiocesium and strontium retention in soils"

Sassi, M.*; Rosso, K. M.*; Okumura, Masahiko; Machida, Masahiko

Clays and Clay Minerals, 65(5), p.371 - 375, 2017/11

https://doi.org/10.1346/CCMN.2017.064078

no abstracts in English

Challenges for enhancing Fukushima environmental resilience, 7; Behavior and abundance of radiocesium in the coastal area off Fukushima

Otosaka, Shigeyoshi; Kobayashi, Takuya; Machida, Masahiko

Nippon Genshiryoku Gakkai-Shi, 59(11), p.659 - 663, 2017/11

It is estimated that about 70% of radiocesium released to the environment by the Fukushima Daiichi nuclear accident was carried to the ocean. In addition to monitoring surveys by the government, oceanographic research by many institutions has revealed the distribution and behavior of the accident-derived radiocesium in the ocean. Numerical simulations are efficiently used in such oceanographic investigations, and further improvements are being made based on findings newly obtained after the accident. In this paper, we review the abundance and behavior of radiocesium in the coastal area of Fukushima, deepen the scientific understanding of the current situation of environmental restoration, and explain the issues to be addressed in the future.