Spatial variations of tritium concentrations in groundwater collected in the southern coastal region of Fukushima, Japan, after the nuclear accident

Koki Kashiwaya,Atsunao Marui,Katsuaki Koike,Reo Ikawa,Shinji Nakaya,Taiki Kubo,Yuta Muto

doi:10.1038/s41598-017-12840-3

Abstract

Spatial variations in tritium concentrations in groundwater were identified in the southern part of the coastal region in Fukushima Prefecture, Japan. Higher tritium concentrations were measured at wells near the Fukushima Daiichi Nuclear Power Station (F1NPS). Mean tritium concentrations in precipitation in the 5 weeks after the F1NPS accident were estimated to be 433 and 139 TU at a distance of 25 and 50 km, respectively, from the F1NPS. The elevations of tritium concentrations in groundwater were calculated using a simple mixing model of the precipitation and groundwater. By assuming that these precipitation was mixed into groundwater with a background tritium concentration in a hypothetical well, concentrations of 13 and 7 TU at distances of 25 and 50 km from the F1NPS, respectively, were obtained. The calculated concentrations are consistent with those measured at the studied wells. Therefore, the spatial variation in tritium concentrations in groundwater was probably caused by precipitation with high tritium concentrations as a result of the F1NPS accident. However, the highest estimated tritium concentrations in precipitation for the study site were much lower than the WHO limits for drinking water, and the concentrations decreased to almost background level at the wells by mixing with groundwater.

Highlights

The huge earthquakes on and after 11 March 2011, the ensuing Tsunami, and the accident at the Fukushima Daiichi Nuclear Power Station (F1NPS) wreaked enormous damage in Japan
River water collected once a year from 16 rivers and one dam under base flow conditions showed elevated tritium concentrations compared to background levels
Yabusaki et al.[9] reported on tritium concentrations for seven groundwater and spring water samples collected from the northern coastal region in Fukushima prefecture, and pointed out the possibility that the tritium concentration was elevated by recharge from precipitation with high tritium concentrations after the F1NPS accident

Summary

Introduction

The huge earthquakes on and after 11 March 2011, the ensuing Tsunami, and the accident at the Fukushima Daiichi Nuclear Power Station (F1NPS) wreaked enormous damage in Japan. River water collected once a year (from 2012 to 2014) from 16 rivers and one dam under base flow conditions showed elevated tritium concentrations compared to background levels Their mean annual concentration decreased consistently from 2012 to 2014. Yabusaki et al.[9] reported on tritium concentrations for seven groundwater and spring water samples collected from the northern coastal region in Fukushima prefecture, and pointed out the possibility that the tritium concentration was elevated by recharge from precipitation with high tritium concentrations after the F1NPS accident. Tritium concentrations in some types of water samples collected around the F1NPS were reported, but the impact of tritium emitted by the accident on groundwater was not systematically evaluated. The water level meter could not be inserted at more than half of the wells because of the well structure, the depth was obtained in most of these cases by interviewing the well owner

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Conclusion