Dr. Tsubokura's Radiation Lecture Vol.102
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
103. Circumstances vary after nuclear accidents
Nuclear accidents are rated according to the International Nuclear Events Scale from Level 0 to Level 7, depending on their impact and intensity. Among global nuclear accidents, those at the Chernobyl power plant in 1986 and Fukushima Daiichi nuclear power plant in 2011 were the only accidents rated Level 7. Although the classification of these two accidents is the same, the circumstances and subsequent countermeasures were not.
First, the type of radioactive materials and their levels were different at Chernobyl and Fukushima. The levels of iodine-131, cesium-137, strontium-90, and plutonium-239 emitted after the nuclear accident at Fukushima were about 1/10th, 1/6th, 1/50th, and 1/10,000th, respectively, of those after the Chernobyl accident.
In particular, levels of strontium and plutonium released from the Fukushima Daiichi nuclear power plant accident were lower compared to the Chernobyl accident. Therefore, almost all of the additional radiation exposure recorded in the Fukushima prefecture today is from cesium. On the other hand, during the Chernobyl accident, 90% of the internal exposure was caused by cesium, and 10% was from strontium. For this reason, the countermeasures taken after the Chernobyl disaster were based on a wider variety of radio