Nuclear accident-derived 3H in river water of Fukushima Prefecture during 2011–2014

Abstract

During 2011–2014, we measured 3H concentrations in river water samples collected during base flow conditions and during several flood events from two small rivers in a mountainous area in Fukushima Prefecture, which received deposition of 137Cs from the Fukushima Dai-ichi Nuclear Power Plant accident. 3H concentrations above background levels were found in water samples collected during both base flow conditions and flood events in 2011. The 3H concentrations during flood events were generally higher than those during base flow conditions. The 3H concentrations in both rivers during base flow conditions and flood events decreased with time after the accident and reached almost background levels in 2013.We also measured 3H concentrations in freshwater samples from 16 other rivers and one dam in eastern Fukushima Prefecture from 2012 to 2014 during base flow conditions. The measured 3H concentrations were higher than the background level in 2012 and decreased with time. The 137Cs inventory in the catchment area at each sampling point was estimated from air-borne monitoring results in the literature and compared with the 3H concentrations. We found surprisingly good correlations between 137Cs inventories in the catchment areas and 3H concentrations in the water samples. Further studies will be necessary to clarify the reason for the good correlation.