3:45 PM - 4:00 PM
[MAG34-07] Estimation of Pathways Based on the Temporal Variation of Oceanic 137Cs Derived from the Fukushima Daiichi Nuclear Power Plant Accident
Keywords:Fukushima Daiichi Nuclear Power Plant, Cs-137, Direct release, river discharge
The accident at the Fukushima Daiichi Nuclear Power Plant (1F NPP) resulted in the release of 137Cs into the environment. Since 137Cs concentrations in the ocean have not recovered to pre-accident levels, it is important to elucidate the supply pathways of 137Cs to the ocean in more detail.
In this study, we attempted to estimate the contribution of each supply pathway at each monitoring station based on the time-series changes in the monitoring data of 137Cs concentrations in the ocean.
Since there is a marked difference between the 137Cs flux directly leaked from the 1F NPP site or nearby areas and that discharged from the river Therefore, we thought it would be possible to estimate the contribution rates of direct release and river discharge by focusing on the time-series changes in the concentration of 137Cs in the ocean. So far, contribution rates have only been estimated by simulation. In this study, we estimated the contribution rate based on the measured 137Cs concentrations in the ocean from March 2012 to July 2016, and the contribution of rivers was estimated by assuming that the rate of decrease of 137Cs concentration in the ocean is determined by the rate of decrease of direct leakage and river discharge.
As a result, the contribution rates from the 1F NPP, the Abukuma River, and the Ukedo River were found to be large in the vicinity of each river. By focusing on the differences in the time-series changes of each river, we were able to estimate the contribution rate of each river, which has not been analyzed in previous studies. The contribution rate estimated in this study showed a high correlation (R2=0.88) with the contribution rate estimated by simulation in the previous study. Given the high correlation between the contribution rates estimated from methods independent of the previous study, the contribution rate estimates made in this study and the previous study are both valid. However, the values do not have a one-to-one correspondence, suggesting that the influence of rivers may have been underestimated in this study.
In this study, we attempted to estimate the contribution of each supply pathway at each monitoring station based on the time-series changes in the monitoring data of 137Cs concentrations in the ocean.
Since there is a marked difference between the 137Cs flux directly leaked from the 1F NPP site or nearby areas and that discharged from the river Therefore, we thought it would be possible to estimate the contribution rates of direct release and river discharge by focusing on the time-series changes in the concentration of 137Cs in the ocean. So far, contribution rates have only been estimated by simulation. In this study, we estimated the contribution rate based on the measured 137Cs concentrations in the ocean from March 2012 to July 2016, and the contribution of rivers was estimated by assuming that the rate of decrease of 137Cs concentration in the ocean is determined by the rate of decrease of direct leakage and river discharge.
As a result, the contribution rates from the 1F NPP, the Abukuma River, and the Ukedo River were found to be large in the vicinity of each river. By focusing on the differences in the time-series changes of each river, we were able to estimate the contribution rate of each river, which has not been analyzed in previous studies. The contribution rate estimated in this study showed a high correlation (R2=0.88) with the contribution rate estimated by simulation in the previous study. Given the high correlation between the contribution rates estimated from methods independent of the previous study, the contribution rate estimates made in this study and the previous study are both valid. However, the values do not have a one-to-one correspondence, suggesting that the influence of rivers may have been underestimated in this study.