Soil decontamination work undertaken after the Fukushima nuclear accident in Japan - mostly by stripping - has reduced radioactive cesium concentrations by 80%, whose lifetime is calculated in hundreds of years; but the problem of forests remains intact, indicates a synthesis of scientific studies.
These stripping works, decided by the Japanese authorities after the Fukushima disaster in March 2011, were carried out on more than 9,000 square kilometers, a region that extends from the area near the nuclear power plant (11 municipalities evacuated) to a larger area of 40 municipalities, affected at lower but significant levels of radioactivity.
Lessons from the first decontamination work
They are now almost completed and, for the first time, researchers are learning from a synthesis of about sixty scientific publications, published in the journal Soil of the European Union of Geosciences. According to this synthesis, " stripping of the topsoil layer to a thickness of 5 centimeters, the main method used by the Japanese authorities to remediate cropland, has reduced cesium concentrations by about 80% in treated areas. ".
This remediation work - which had not been done after the Chernobyl disaster - was therefore " effective " and allowed "to verify in the field that the radiocaesium remains in the upper layers of the soil ". affirmed to AFP Olivier Evrard, researcher at the Laboratory of climate and environmental sciences (CEA / CNRS / University of Versailles St-Quentin-en-Yvelines), and coordinator of the publication. The researcher recalls that Cesium 137 " is the highest risk for the population in the medium and long term, because it can be estimated that there will remain about three centuries in the environment in the absence of decontamination action ".
The lessons of soil decontamination at #Fukushima, a publication coordinated by Olivier Evrard, researcher at #LSCE_IPSL to find 👉 https://t.co/U8Fd92PBEf. This study provides an overview of the #contamination strategies used and their effectiveness. #Japan #sol pic.twitter.com/Aaqt3EG0mhCEA_Officiel (@CEA_Officiel) December 12, 2019
" Hard to treat " waste
The cost of this decontamination is nevertheless extremely high: the removal of the superficial part of the topsoil " cost the Japanese State about 24 billion euros, " the authors of the summary said in a statement. The technique also generates a large amount of waste (20 million m3), " difficult to treat ".
But above all, this work did not concern the forests, which cover " three quarters of the affected area ". Intact, they are therefore " a potential long-term reservoir of radiocaesium, " warn scientists. However, these forests are subject to soil erosion, with typhoons, floods and landslides, which can lead to contamination of the river system. Another method of decontamination " phytoextraction " (already tested at Chernobyl), has been evaluated: it consists of planting plants that pump cesium from the soil. " But studies show us that the yield is not good, " says Olivier Evrard.
( with AFP )
► [Reportage] Fukushima: 8 years later, the life of the Japanese remains difficult