Radiological Conditions in the Environment around the Fukushima Daiichi Nuclear Power Plant Site

摘要

Large-scale environmental monitoring that has been repeatedly performed has revealed the characteristics of radiological conditions around the Fukushima NPP site. Several radionuclides other than radiocesium were detected three months after the accident, but radiocesium turned out to be far more important than the other radionuclides from the viewpoint of long-term exposures. Radiocesium deposition was found to be heterogeneous at different scales. On the one hand, air dose rates in environments related to human living have decreased much faster than the physical decay of radiocesium; on the other hand, the reduction has been close to physical decay in pure forests. Movement of deposited radiocesium has generally been very slow except in urban areas, while radiocesium deposited on the ground has gradually penetrated into the ground, resulting in decreased air dose rates because of the increased radiation shielding effect.