Following the accident at the Fukushima Daiichi nuclear plant in March 2011, the Japanese authorities carried out major decontamination works in the affected area, covering more than 9000 square kilometers. With most of this work completed, the scientific journal SOIL of the European Geosciences Union (EGU) on 12 December published a synthesis of approximately 60 scientific papers, that together provide an overview of the decontamination strategies used and their effectiveness dealing with radiocaesium. This work is the result of an international collaboration led by Olivier Evrard, a researcher at the Laboratory of Climate and Environmental Science at Université Paris Saclay.
Soil decontamination began in 2013 and has now been nearly completed in the identified priority areas in Fukushima Prefecture. A decision was taken in November 2011 to decontaminate eleven municipalities evacuated after the accident, and a futher 40 non-evacuated municipalities affected by lower levels of radioactivity. However, areas that are difficult to access have not yet been decontaminated.
The research indicates that removing the surface layer of the soil to a thickness of 5cm – the main method used by the Japanese authorities to clean up cultivated land – reduced caesium concentrations by about 80% in treated areas. However, removing the uppermost part of the topsoil, which has proved effective in treating cultivated land, cost the Japanese state about €24 billion ($26.6bn). It also generated a significant amount of waste, which is difficult to treat, transport and store pending shipment to final disposal sites outside Fukushima prefecture by 2050. By early 2019, Fukushima’s decontamination efforts had generated about 20 million cubic metres of waste.