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

摘要

Cs-137 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. Cs-137 inventories in soils surrounding SU, FS, IZ, and KM were 6.4, 2.9, 2.1, and 0.9 MBq m(-2), respectively. Cs-137 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 Cs-137 inventories in bottom sediment than those of soil in SU and FS suggest that Cs-137 was delivered to and accumulated in these ponds. Mean total Cs-137 activity concentrations in SU, FS, IZ, and KM were 41, 13, 9.5, and 1.4 Bq L-1, respectively. Particulate Cs-137 concentration accounted for 71-90% of total Cs-137 in the water samples, on average. The mean distribution coefficient, K-d, in SU, FS, IZ, and KM was 1.3 x 10(5), 2.1 x 10(5), 1.7 x 10(5), and 6.2 x 10(5) L kg(-1), respectively. These K-d values were higher than the K-d values observed in the Chernobyl area by 1-2 orders of magnitude. Although no significant decreasing trends were found, dissolved Cs-137 activity concentration tended to be low during winter in all four ponds. Dissolved Cs-137 activity concentrations were proportional to K+ and DOC concentrations in all the ponds. The results from principal component analysis performed for Cs-137 activity concentration and water chemistry data sets suggested that there were different mechanisms behind variability of dissolved Cs-137 activity concentrations for each pond. Continuous monitoring is required to reveal temporal trends in Cs-137 activity concentrations of these waters and controlling factors of such in closed water systems in Fukushima. (c) 2017 Elsevier Ltd. All rights reserved.