Radionuclide pollution inside the Fukushima Daiichi exclusion zone, part 1: Depth profiles of radiocesium and strontium-90 in soil

In June 2013 and July 2014, soil samples were collected from unremediated locations within Fukushima prefecture, with special focus on the Fukushima exclusion zone. The soil samples were analyzed for radiocesium by gamma spectroscopy, and then 90Sr by liquid scintillation counting (LSC) after ion specific extraction chromatography. Activity concentrations are compared between sampling years, sampling sites, and soil layers, revealing a general downward trend in activities but also some inconsistencies. Maximum activity concentrations of 137Cs in soil were found in close vicinity of the gate of Fukushima Daichi Nuclear Power Plant and reached up to 106 Bq·kg−1 in 2013. Thirteen months later, these maximum levels were lower by a factor of at least 5. Activity ratios of 90Sr/137Cs were usually around 2 · 10−4, but locally increased to the 10−3 range, and in one spot even to the 10−1 range. Finally, attempts were made to analyze rare radionuclides in environmental samples from this area, in particular tritium (3H) and 60Fe, however no traces were found in the vegetation and soil samples, respectively.