Following the terrible accident in Fukushima, the Japanese authorities decided to carry out major decontamination work in the affected region. However, this project is now largely complete. What do you need to know about this unprecedented work?
On March 11, 2011, a magnitude 9.1 earthquake followed by a terrible tsunami caused the total shutdown of the main cooling system at the Fukushima Daiichi nuclear power plant (Japan). What followed was a meltdown of the cores of reactors 1, 2 and 3 as well as the overheating of the spent fuel pool of reactor 4. This terrible accident, which caused more than 18,000 deaths, also had a major impact on the 'environment , well beyond Japan.
You should know that the Japanese authorities then decided to carry out major soil decontamination work in the Fukushima area. However, this incredible project concerns an area of more than 9,000 km²! In a publication in the journal SOIL on December 12, 2019, the French researcher Olivier Evrard (CNRS/CEA) presents the synthesis of some sixty scientific publications on the subject. The goal? Provide an overview of the decontamination strategies used, as well as their effectiveness.
Recall that during the disaster, radioactive cesium was emitted in large quantities. However, one of the isotopes of cesium (137Cs) has a half-life of 30 years and this represents the greatest threat to the population in the medium and long term. Indeed, in the absence of decontamination, this cesium could remain approximately 300 years in the environment ! Nevertheless, after seven years of work, the cesium concentrations in the treated areas have been reduced by 80%.
According to the summary, these encouraging results are the result of a technique adopted by the Japanese authorities. The latter was intended to clean up cultivated land. This is a stripping of the surface layer of the soil to a thickness of 5 cm. Incidentally, this work cost the Japanese state around 24 billion euros.
Nevertheless, how not to mention the large amount of waste that must be transported, stored and processed? At the beginning of 2019, the authorities had counted no less than 20 million cubic meters waste from decontamination work. These will be stored for years near the plant but should then be sent elsewhere. There is talk of final storage sites outside Fukushima prefecture, and this by 2050.
It should be noted that the decontamination mainly concerned agricultural landscapes as well as residential areas. Unfortunately, the forests have not been treated, although the latter represent 75% of the surfaces located within the radioactive plume! The reasons given by the authorities mainly concern the astronomical costs of such an undertaking.
And yet, the consequences for people and the environment are far from negligible. Indeed, forests now represent an important reservoir of radioactive cesium which could be "redistributed" in the future, through the landscapes. Several events can be at the origin of this redistribution:soil erosion, floods, landslides, as well as typhoons. The fear of the researchers relates in particular to the possibility that the remediated areas are again contaminated.
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