Behavior of 137Cs in ponds in the vicinity of the Fukushima Dai-ichi nuclear power plant

Publication date: November 2017
Source:Journal of Environmental Radioactivity, Volumes 178–179
Author(s): Yoshifumi Wakiyama, Alexei Konoplev, Toshihiro Wada, Tsugiko Takase, Ian Byrnes, Matthew Carradine, Kenji Nanba
¹³⁷Cs activity concentration in the water of four ponds, Suzuuchi (SU), Funasawa (FS), Inkyozaka (IZ), and Kashiramori (KM), that are within 10 km of the Fukushima Dai-ichi nuclear power plant were observed from April 2015 to August 2016. ¹³⁷Cs inventories in soils surrounding SU, FS, IZ, and KM were 6.4, 2.9, 2.1, and 0.9 MBq m⁻², respectively. ¹³⁷Cs inventories in the bottom sediments of SU, FS, IZ, and KM were 13, 8.9, 1.6, and 1.1 MBq m⁻², respectively. Higher ¹³⁷Cs inventories in bottom sediment than those of soil in SU and FS suggest that ¹³⁷Cs was delivered to and accumulated in these ponds. Mean total ¹³⁷Cs activity concentrations in SU, FS, IZ, and KM were 41, 13, 9.5, and 1.4 Bq L⁻¹, respectively. Particulate ¹³⁷Cs concentration accounted for 71–90% of total ¹³⁷Cs in the water samples, on average. The mean distribution coefficient, Kd, in SU, FS, IZ, and KM was 1.3 × 10⁵, 2.1 × 10⁵, 1.7 × 10⁵, and 6.2 × 10⁵ L kg⁻¹, respectively. These Kd values were higher than the Kd values observed in the Chernobyl area by 1–2 orders of magnitude. Although no significant decreasing trends were found, dissolved ¹³⁷Cs activity concentration tended to be low during winter in all four ponds. Dissolved ¹³⁷Cs activity concentrations were proportional to K⁺ and DOC concentrations in all the ponds. The results from principal component analysis performed for ¹³⁷Cs activity concentration and water chemistry data sets suggested that there were different mechanisms behind variability of dissolved ¹³⁷Cs activity concentrations for each pond. Continuous monitoring is required to reveal temporal trends in ¹³⁷Cs activity concentrations of these waters and controlling factors of such in closed water systems in Fukushima.



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