Radiocesium decontamination of a riverside in Fukushima, Japan

Area of Science:

• Environmental Science
• Radiological Protection
• Nuclear Engineering

Background:

• Fukushima Dai-ichi nuclear disaster necessitated extensive decontamination.
• Standard topsoil removal is ineffective for contaminated river sediments.
• Radiocesium contamination in river systems presents unique challenges.

Purpose of the Study:

• To test a targeted decontamination strategy for radiocesium in a Fukushima river tributary.
• To assess the effectiveness of sediment removal based on spatial radiocesium distribution.
• To evaluate potential radiation exposure during recreational and educational use of the decontaminated area.

Main Methods:

• Assessed spatial distribution of radiocesium (¹³⁷Cs, ¹³⁴Cs) in flood channel and riverbed sediments.
• Removed contaminated sediment (15-35 cm depth) and dike slope soil (5 cm depth) based on activity concentration.
• Calculated annual external doses for potential future use of the area.

Main Results:

• Radiocesium distribution in sediments was highly heterogeneous, with hotspots exceeding 10 kBq/kg at 25 cm depth.
• Targeted sediment removal significantly reduced air dose rates by approximately 50%.
• Calculated annual external doses for commuting and outdoor education were minimal (1-2% of daily life exposure).

Conclusions:

• The developed decontamination measure effectively reduced radiation exposure in the Abukuma River tributary.
• Targeted sediment removal based on spatial analysis is a viable strategy for riverine decontamination.
• The decontaminated area poses limited radiation risk for public use, including educational activities.