Long-term behavior of 137Cs and 3H activities from TEPCO Fukushima NPP1 accident in the coastal region off Fukushima, Japan
Decreasing trends of both 137Cs and 3H activity concentrations and an increasing trend of 3H/137Cs activity ratio at Fukushima Dai-ichi Nuclear Power Plant, FNPP1, were observed. Homogeneous distribution of 3H were observed off Fukushima and 3H activity concentrations ranged from 60 to 200 Bq m−3 in 2014. Contribution by relatively 3H rich water from surrounding rivers might be larger source of 3H rather than flux of 3H from FNPP1. Possibilities of observed high and variable 3H/137Cs activity ratio close to FNPP1 site may be evaporation of 3H or sporadic release of 3H rich/poor water from the site.
Keywords137Cs 3H Fukushima accident Activity ratio River water
The author thanks Rika Hozumi for her extraction work of caesium from seawater samples, Tomoni Onda for her work to prepare database and tables used in this study and Junkho Inomata, Kenji Watanabe and Azusa Goto for their support to collect seawater samples at Tomioka since June 2014. The author also thanks Satoshi Nakamura for collecting seawater samples at Hasaki at the research pier of Hazaki Oceanographical Research Station of the Port and Airport Research Institute since April 2011. The authors also thanks Yasunori Hamajima for his contribution to measure extracted caesium samples at Ogoya, Yukiko Suda for her work to handle spectra data of measured extracted caesium. A part of this work was supported by JSPS KAKENHI Grant Number JP15K00520 and by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan, (KAKENHI No. #24110005. A part of coastal observations at Tomioka and Hasaki presented in this article was supported by EC 7th Framework project COMET-FRAME (COordination and iMplementation of a pan-Europe instrumenT for radioecology) (Grant Agreement Number 604974) and a Marine Project of Institute of Environmental Radioactivity, Fukushima University, Japan. This article is based on two presentations and discussions, “IA-520 [Invited Talk] Long Term Behavior of TEPCO Fukushima NPP1 Accident Radiocaesium in the Coastal Region of Japan and the North Pacific Ocean, Past and Present: A Review” and “A-022 Radiocaesium in Surface Water Observed in Winter 2015/2016 in Both Coastal Regions of Japan and the Western North Pacific Ocean” at APSORC 17–6th Asia–Pacific Symposium on Radiochemistry held at ICC Jeju, Jeju Island, Korea on 17–22 September 2017.
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