A modeling approach to estimate 3H discharge from rivers: Comparison of discharge from the Fukushima Dai-ichi and inventory in seawater in the Fukushima coastal region.

Abstract Estimation of 3H discharge from river catchments is important to evaluate the effect of Fukushima Dai-ichi discharge and future planned 3H release to the ocean on the coastal environment. Using a previously developed model based on the tank model and observed 3H concentration in river water, the 3H discharge from the Abukuma River and 13 other rivers in the Fukushima coastal region were estimated from June 2013 to March 2020. The 3H discharge from catchments of the Abukuma River and 13 other rivers in the Fukushima coastal region during 2014–2019 were estimated to be 1.2–4.0 TBq/y. These values were approximately 2–22 times larger than the annual 3H discharge from the Fukushima Dai-ichi after 2016, indicating the significance of 3H discharge from the catchments through the rivers. This estimation is expected to be useful to evaluate and predict 3H concentrations and inventories in the Fukushima coastal region for consideration of planned 3H release to the ocean.