THE Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 resulted in the radioactive contamination of the Japanese landscape. Accordingly, the authorities decided to conduct extensive remediation activities in the impacted region to allow for the relatively rapid return of the local population.
In November 2011, it was decided to decontaminate 11 municipalities evacuated after the accident and 40 non-evacuated municipalities affected by lower levels of radioactivity in the Fukushima Prefecture. Decontamination activities predominantly targeted agricultural landscapes and residential areas. No decontamination activities are planned for the majority of forested areas, which cover about 75 per cent of the main contaminated area. With most of the work now completed, the European Geosciences Union (EGU) recently published an assessment of the effectiveness of the strategies used, with a focus on radioactive caesium. This isotope was emitted in large quantities during the accident, contaminating more than 9,000 square kilometres of area. The study, conducted by an international group of researchers led by Olivier Evrard of the Laboratory of Climate and Environmental Sciences at Université Paris Saclay, has been published in “Soil”, an open access journal of the EGU.
According to World Nuclear News (WNN), the assessment indicates that removing the surface layer of the soil to a thickness of five centimetres— the main method used for cleaning up cultivated land—has reduced caesium concentrations by around 80 per cent in treated areas. The removal of this soil has cost the government some €24 billion ($27 billion) and until early 2019 generated about 20 million cubic metres of waste.
According to the authors of the study, although the impact of decontamination on the radioactive dose rates for the local population remains a subject of debate in the literature and among the local communities, outdoor workers in the special decontamination zone (of 1,117 sq. km area) represent a group of the local population that may exceed the long-term dosimetric target of one millisievert/year.
The researchers suggest that the volume of waste generated by decontamination may be decreased through incineration of combustible material and recycling of the less contaminated soil for civil engineering structures. However, they have pointed out that most of the material will have to be stored for about 30 years at interim facilities, which were opened in 2017 in the vicinity of the FDNPP, before being transported to final disposal sites outside the Fukushima Prefecture. The analysis also recommends further research on issues associated with the recultivation of decontaminated agricultural land, the monitoring of the contribution of radioactive contamination from forests to rivers that flow across the region, and the return of inhabitants and their reappropriation of the territory after evacuation and decontamination. This will be undertaken by a Franco-Japanese collaboration over a period of five years beginning 2020.
“The feedback on decontamination processes is unprecedented because it is the first time that such a major clean-up effort has been made following a nuclear accident,” WNN quoted Evrard. “The Fukushima accident gives us valuable insights into the effectiveness of decontamination techniques, particularly for removing caesium from the environment,” Evrard said.