Outline of the Fukushima Daiichi Nuclear Power Plant (FDNPP) Accident

To accurately assess the current status of environmental radioactive contamination in FDNPP accident, it is necessary to understand the dynamics of radionuclides in the environment in the initial phase immediately after the Fukushima nuclear accident. Because the topography and weather in Japan are involved, it is difficult to accurately reproduce the behavior of radionuclides released from the FDNPP reactors. Furthermore, power lines were cut off in many areas of East Japan, including Tokyo, because of the effects of the Great East Japan Earthquake disaster. Therefore, many radiation monitoring systems failed immediately after the earthquake. As a result, available radiation monitoring data in East Japan are very limited. In this chapter, the situation in the early stage of the FDNPP accident is reviewed, and the behavior and amount of radioactive materials released from the broken reactor to the environment are considered. The author was unable to directly measure the status of radioactive contamination and changes in radiation dose on the FDNPP premises during this period. The data used for the discussions are based on those published by TEPCO.