Effectiveness of Fukushima decontamination studied

The study - Effectiveness of landscape decontamination following the Fukushima nuclear accident: A review - is the result of an international collaboration led by Olivier Evrard, researcher at the Laboratory of Climate and Environmental Sciences at Université Paris Saclay.

In Fukushima Prefecture, the decision was taken in November 2011 to decontaminate 11 municipalities evacuated after the accident and the 40 non-evacuated municipalities affected by lower levels of radioactivity. Decontamination activities, aimed at allowing for a relatively rapid return of the local population, predominantly targeted agricultural landscapes and residential areas. No decontamination activities are currently planned for the majority of forested areas, which cover about 75% of the main contaminated area.

The study focuses mainly on the fate of radioactive caesium in the environment because this isotope was emitted in large quantities during the accident, contaminating an area covering more than 9000 square kilometres. Its findings indicate 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 - has reduced caesium concentrations by around 80% in treated areas. The removal of this soil has cost the government some EUR24 billion (USD27 billion) and has generated a significant volume of waste. By early 2019, about 20 million cubic metres of waste had been generated.

The analysis recommends further research on: the issues associated with the recultivation of decontaminated agricultural land; the monitoring of the contribution of radioactive contamination from forests to the rivers that flow across the region; and, the return of inhabitants and their reappropriation of the territory after evacuation and decontamination. This research will be the subject of a French-Japanese and multidisciplinary international research project, Irradiation Measurement Human Tolerance via Environmental Tolerance (MITATE), led by the French National Centre for Scientific Research (CRNS) and Japanese organisations, which will start in January 2020 for an initial period of five years.

"The feedback on decontamination processes following the Fukushima nuclear accident is unprecedented because it is the first time that such a major clean-up effort has been made following a nuclear accident," said Evrard. "The Fukushima accident gives us valuable insights into the effectiveness of decontamination techniques, particularly for removing caesium from the environment."