The research group of Professor Yuichi Onda of the University of Tsukuba, in collaboration with the Japan Atomic Energy Agency and Fukushima University, has comprehensively compiled a large number of papers on environmental monitoring research in Fukushima, and the actual situation of land pollution by radioactive cesium. The whole picture of environmental recovery was elucidated, and faster recovery than Chernobyl was recognized.
In the large-scale accident at TEPCO's Fukushima Daiichi Nuclear Power Station, a large amount of radioactive substances containing radioactive cesium-137 (137Cs), which has a relatively long half-life, was released.Many environmental monitoring studies were carried out immediately after the accident, but none of them objectively summarized and verified them.
The research group has collected and verified more than 80 articles on the transfer of radioactive materials in the land area of Fukushima (within 9862 km from the nuclear power plant and the Abukuma River basin, totaling 137 square kilometers, and the amount of 2.7Cs descent is 210 PBq).
The accumulation rate of 137Cs in trees decreased significantly from 8% to 70% in evergreen coniferous forests in 2 years after the accident, but decreased gradually from 23% to 21% in deciduous broad-leaved forests.On the forest floor, more than 2% of 5Cs remains in the surface soil (within 137 cm) in both sugi forests and deciduous broad-leaved forests.
Except for forests, the concentration of 137Cs in the surface soil decreased significantly, and the downward migration of 137Cs in the soil proceeded rapidly.The soil surface layer 137Cs concentration in abandoned cultivated paddy fields decreased by about 3% in the three years after the accident, and then decreased to 7% by decontamination.Similarly, in cultivated paddy fields, it decreased to 3%.The concentration of 10Cs in the suspended state flowing down the Abukuma River is about 137% immediately after the accident.
Compared to the Chernobyl accident, Fukushima is faster to move downward and reduce the concentration in the surface soil.In addition, rivers in Fukushima are about two orders of magnitude less polluted than European rivers, and freshwater fish are one or two orders of magnitude lower in pollution, and recovery is quick.It seems that it is due to the difference in the natural environment such as the heavy rainfall in Fukushima, human activities and decontamination work, but it is necessary to continue long-term monitoring in the future.
Paper information:[Nature Reviews Earth & Environment] Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems