1:45 PM - 3:15 PM
[MAG34-P03] Temporal changes of 137Cs dynamics after decontamination at an urban pond
Keywords:Fukushima Dai-ichi Nuclear Power Plant accident, 137Cs, pond, decontamination, urban area
Many ponds in Fuksuhima Prefecture were contaminated by radiocesium (134Cs, 137Cs) due to the Fukushima Dai-ichi Nuclear Power Plant accident. The decontamination and/or countermeasures against radioactive materials were considered for the ponds accumulated high radiocesium concentration. The bottom sediment removal, one of the countermeasures, decrease the radiocesium concentration in bottom sediment by removing bottom sediment. Decontamination lowered 137Cs inventory and 137Cs concentration in bottom sediment (Katengeza et al., 2021; Kurosawa et al., submitted) and 137Cs concentration in pond water (Kurosawa et al., submitted). According to previous study (Funaki et al., 2018; Hayashi and Tsuji, 2020; Takechi et al., 2021; Wakiyama et al., 2017), 137Cs tended to flow into and accumulate in ponds and dam reservoirs secondarily, therefore, it is necessary to understand the process of 137Cs accumulation after decontamination. The 137Cs concentration in Suspended Solids (SS) and dissolved 137Cs concentration in urban water (Tsuji et al., 2019; Yamashita et al., 2015) was higher than in non-urban river. However, few studies investigated the temporal changes of 137Cs dynamics after decontamination in urban area. The objective of this study was to clarify the 137Cs accumulation after decontamination and effect of urban area.
The study pond is located in the central area of Koriyama city, Fukushima Prefecture. The amount of 137Cs deposited around the investigated pond was 0.170 MBq/m2. The study pond was decontaminated by dredging of bottom sediment in 2017. The bottom sediment, pond water, inflow water, outflow water and river water around the study pond were collected from 2018 to 2021 and analyzed for 137Cs concentration.
After decontamination, the average 137Cs inventory at 7 sites ranged from 0.270 to 0.313 MBq/m2. The average 137Cs inventory was not changed after decontamination, however, the variability 137Cs inventory increased year by year. At sites where 137Cs inventory tended to decrease, 137Cs concentration decreased year by year and 137Cs penetration became shallower. At sites where 137Cs inventory tended to increase, 137Cs penetration was deeper year by year. The 137Cs concentration in pond water tended to decrease after decontamination. The 137Cs concentration in SS and dissolved 137Cs concentration decreased from 27.6 kBq/kgDW to 13.6 kBq/kgDW and from 0.0482 Bq/L to 0.0223 Bq/L, respectively. The average 137Cs concentration in SS of inflow water during normal and rainfall event was 5.71 kBq/kgDW and 13.0 kBq/kgDW, respectively. The average total 137Cs concentration (dissolved 137Cs concentration+particulate 137Cs concentration) in outflow water during normal and rainfall event was 0.309 Bq/L and 1.32 Bq/L, respectively. The total 137Cs concentration in outflow water during normal and rainfall event tended to be higher than in inflow and pond water, suggesting that 137Cs tended to discharge. The 137Cs concentration in SS and dissolved 137Cs concentration in river water after passing through the urban area was about 16 times higher than before entering the urban area, suggesting that the 137Cs concentration in SS and dissolved 137Cs concentration in river water in urban area was high. It was suggested that the 137Cs level in the study pond kept high after decontamination because of the inflow of high 137Cs concentration in SS and dissolved 137Cs concentration from urbanized catchment area.
The study pond is located in the central area of Koriyama city, Fukushima Prefecture. The amount of 137Cs deposited around the investigated pond was 0.170 MBq/m2. The study pond was decontaminated by dredging of bottom sediment in 2017. The bottom sediment, pond water, inflow water, outflow water and river water around the study pond were collected from 2018 to 2021 and analyzed for 137Cs concentration.
After decontamination, the average 137Cs inventory at 7 sites ranged from 0.270 to 0.313 MBq/m2. The average 137Cs inventory was not changed after decontamination, however, the variability 137Cs inventory increased year by year. At sites where 137Cs inventory tended to decrease, 137Cs concentration decreased year by year and 137Cs penetration became shallower. At sites where 137Cs inventory tended to increase, 137Cs penetration was deeper year by year. The 137Cs concentration in pond water tended to decrease after decontamination. The 137Cs concentration in SS and dissolved 137Cs concentration decreased from 27.6 kBq/kgDW to 13.6 kBq/kgDW and from 0.0482 Bq/L to 0.0223 Bq/L, respectively. The average 137Cs concentration in SS of inflow water during normal and rainfall event was 5.71 kBq/kgDW and 13.0 kBq/kgDW, respectively. The average total 137Cs concentration (dissolved 137Cs concentration+particulate 137Cs concentration) in outflow water during normal and rainfall event was 0.309 Bq/L and 1.32 Bq/L, respectively. The total 137Cs concentration in outflow water during normal and rainfall event tended to be higher than in inflow and pond water, suggesting that 137Cs tended to discharge. The 137Cs concentration in SS and dissolved 137Cs concentration in river water after passing through the urban area was about 16 times higher than before entering the urban area, suggesting that the 137Cs concentration in SS and dissolved 137Cs concentration in river water in urban area was high. It was suggested that the 137Cs level in the study pond kept high after decontamination because of the inflow of high 137Cs concentration in SS and dissolved 137Cs concentration from urbanized catchment area.