Twelve years after the nuclear accident that occurred in Fukushima in March 2011, radioactive contamination remains a major concern in north-eastern Japan. The Japanese authorities completed an unprecedented decontamination programme. The central objective was to not expose local inhabitants to excessive radioactive doses. At the onset of the full reopening of the Difficult-to-Return Zone in 2023, the current review provides an update of a previous synthesis published in 2019.

This dataset provides an original compilation of radioactive dose rates and artificial radionuclide activities in sediment deposited after floods in the rivers draining the main radioactive pollution plume in Fukushuma, Japan, between November 2011 and November 2020. In total, 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns were analysed. This provides a unique post-accidental dataset to better understand the environmental fate of radionuclides.

The method for reconstructing the long-term dependence of radionuclide concentrations in rivers and reservoirs based on their vertical distribution in bottom sediments is proposed. Reconstructed time dependencies of particulate and dissolved Cs-137 activity concentrations in the Upa River were found to be described well by the semi-empirical “diffusion” model.