Flow filtration/adsorption and simultaneous monitoring technologies of radiocesium 137Cs in river water

This study develops a method that combines a radiation-grafting fibrous Cs-adsorbent filter of ammonium molybdophosphate (AMP) and a Ce:Gd3Al2Ga3O12 scintillator-based gamma-ray detector for in situ measurements of the activity concentrations of 137Cs in a continuous water flow. To ensure adequate performance, the study locations were set along an upper tributary stream of the Ukedo River and a nearby spring-fed stream, approximately 30 km northwest of the Fukushima Daiichi Nuclear Power Plant. In the tributary stream, the activity concentrations of 137Cs slowly decreased from 19 to 1.7 mBq/L between 2018 and 2020 until reaching equilibrium with a few millibecquerels in 10 years after the accident. This equilibrium value is significantly below the admissible radiocesium activity (10 Bq/L) for drinking water. The spring-fed stream rarely included 137Cs. The monitoring results support previous views about the environmental fate of 137Cs in a forest ecosystem at the Abukuma granitic catchments. The major advantage of this method is that utilizing fibrous Cs adsorbents with AMP-loaded graft chains enables the effective accumulation of 137Cs through a large amount of stream water. Therefore, 137Cs gamma-rays can be detected simultaneously, and combining these strategies provide a unique monitoring platform for on-site and real-time detection of 137Cs at the trace level.