EGU21-14420
https://doi.org/10.5194/egusphere-egu21-14420
EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Behavior of 129I in the Abukuma River water during two high-flow events in 2018

Yoshifumi Wakiyama1, Masumi Matsumura2, Tetsuya Matsunaka3, Shigekazu Hirao1, and Kimikazu Sasa2
Yoshifumi Wakiyama et al.
  • 1Fukushima University, Institute of Environmental Radioactivity, Fukushima, Japan (wakiyama@ipc.fukushima-u.ac.jp)
  • 2Tandem Accelerator Complex, University of Tsukuba, Japan
  • 3Institute of Nature and Environmental Technology, Kanazawa University, Japan

Radioiodine is one of the most important radionuclides released by the accidents of Fukushima Dai-ichi nuclear power plant (FDNPP). Iodine-131 elevated ambient radiation dose rate immediately after the accident, but it is extinguished due to its short half-life. The long-lived 129I can be used as a tracer to retrospectively infer the level of 131I. Understanding of environmental behavior of 129I is important for preparedness against nuclear disaster. This study presents sampling campaigns on the Abukuma River during two high flow events, and discusses riverine 129I behavior based on comparisons with that of 137Cs. The study site was the Kuroiwa site locating at midstream of the Abukuma river. Its catchment area was 2886 km2 and mean 129I inventory in the catchment was 0.041 Bq m-2. Five and seven river water samples were taken during high-flow events in July 2018 (JUL18) and October 2018 (OCT18), respectively. Suspended sediment and filtrate samples were obtained by decantation and subsequent filtration with 0.45 μm-mash membrane filter, respectively. The suspended sediment and filtrate samples were measured for 137Cs activity concentrations with HPGe detector and then measured for 129I/127I ratio with accelerator mass spectrometer and for 127I concentration with ICP-QQQ-MS. Mean 129I activity concentration in suspended sediment during JUL18 and OCT18 were 1.0 and 0.43 mBq kg-1, respectively. In terms of temporal trends, 129I activity concentration in suspended sediment lowered in the peak water discharge phase, contrastive to those of 137Cs which were the highest at peak water discharge phase. Mean dissolved 129I activity concentrations during JUL18 and OCT18 were 0.18 and 0.067 μBq L-1, respectively. Both 129I and 137Cs activity concentrations in dissolved form tended to decrease with time during two high-flow events. Mean apparent distribution coefficient (Kd) during JUL18 and OCT18 were 4.3 ×104 and 6.1 ×103 L kg-1, respectively. The Kd values of 129I were lower than those of 137Cs and it reveal relatively-high solubility of 129I. Total exportation of 129I from the catchment during JUL18 and OCT18 were estimated as 1.0 × 104 and 2.3 × 104 Bq, respectively. Exported 129I in dissolved form accounted for 80 and 27% of total exportations, respectively. By contrast, more than 95% of 137Cs was exported in particulate form in the events. These results indicated an importance of dissolved form for understanding environmental behavior of radioiodine.

How to cite: Wakiyama, Y., Matsumura, M., Matsunaka, T., Hirao, S., and Sasa, K.: Behavior of 129I in the Abukuma River water during two high-flow events in 2018, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14420, https://doi.org/10.5194/egusphere-egu21-14420, 2021.

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