Distribution of strontium-90 in soils affected by Fukushima dai-ichi nuclear power station accident in the context of cesium-137 contamination

Abstract

90Sr and 137Cs activity concentrations were determined by radiometric methods in 76 soil samples (soil, litter, rain gutter deposit, and roadside sediment samples) affected by the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident and collected from the Fukushima exclusion zone. The 90Sr and 137Cs activity concentrations were in the range of 3 to 1050 Bq kg−1 (median 82 Bq·kg−1) and 0.7 to 6770 kBq·kg−1 (median 890 kBq·kg−1), respectively (decay correction date: March 15, 2011). A strong positive correlation was found between 90Sr and 137Cs activity concentration and higher mobility of 90Sr was confirmed in Japanese soil samples. The activity ratio of 90Sr/137Cs in 85% of all samples was in the range of 5.0 × 10−5 to 5.0 × 10−4 with a median of 1.2 × 10−4. From the activity ratio values it was concluded that the 90Sr released to the atmosphere was only around 0.0003–0.02 PBq which is negligible compared to the Chernobyl accident (∼10 PBq) or other nuclear accident contaminations. From the standpoints of radioecology and radiation safety, 137Cs remains the primary pollutant of the FDNPS accident.