January 29, 2024  9th IER seminar of FY2023 was held. ＜Project Professor Konoplev＞

Institute of Environmental Radioactivity (IER) regularly holds the IER seminar in which the faculty members report on their research results, with the aim of facilitating their research activities and promoting communication.

In the 9th IER seminar of this fiscal year that was held on January 29, 2024, a presentation was given by Project Professor Aleksei KONOPLEV to 24 participating researchers and students as follows.

An equation has been derived describing seasonal variations of dissolved radiocesium in water bodies considering two key parameters: water temperature and combined concentration of basic competitive cations. In Fukushima rivers, which are mostly shallow and fast flowing, ammonium concentration is usually negligible. For them the predominant factor of dissolved ¹³⁷Cs seasonality is temperature dependence of ¹³⁷Cs desorption. For stagnated stratified waters of ponds, lakes and dam reservoirs in anoxic conditions, the role of ammonium in ¹³⁷Cs mobilization can be comparable with that of water temperature or even be prevalent.

Results of a field experimental study of dissolved ¹³⁷Cs seasonality in three ponds of Okuma town, which is located in difficult-to-return zone of the Fukushima Daiichi nuclear power plant, were presented. Comparison of in situ and laboratory filtration results has shown the validity of laboratory filtration for dissolved ¹³⁷Cs monitoring in water bodies. The proposed model and derived equation describe reasonably well the seasonality of dissolved ¹³⁷Cs in the investigated ponds.

After the presentation, many questions and comments were raised by IER faculty members, and deep and long discussions about physico-chemical mechanisms of dissolved ¹³⁷Cs in water bodies took place.