Abstract
The 2011 off the Pacific coast of Tohoku Earthquake occurred Friday 11 March, 14:46 (Japan Standard Time, JST). The earthquake and tsunami inflicted serious damages on the Fukushima 1 nuclear power plant, especially the cooling functions. On 15 March, radioactive dust was escaping from the power plant. For serious situation on 14 April, we summarize the diffusion of radioactive matter and impacts against the environment. We point out the following: (1) The diffusing distances are different according to the direction. Such facts show that the radiation exposure is caused by radioactive dust, which is moved and sunk by wind and rain. (2) The ambient dose rates in Fukushima prefecture are accumulated during 737 h and they are compared with those of 2010. There is a village where the rate is 7.6 mSv. We optimize an expression of the ambient dose rate for the village, and integrate it. We get 41.1 mSv/year. The village is 40 km NW from the nuclear power plant. By using the same way, we predict the accumulated rate of Fukushima city, and get 16.2 mSv/year. (3) The soil of the village radiates 1.63 × 105 or 2.2 × 105 Bq/kg from 137Cs. The values are detected on 20 March and 26 March. The residence half-time for 131I is 9.6 d. We calculate the half-time of the water in a pond, and get 11 d and 7.2 d for 137Cs and 131I. (4) We find two monitoring points of 162 and 293 mSv/year, which are 30 km and 20 km in NW direction.
