Reconstruction of radioiodine deposition in the environment and dose evaluation following the accident at the Fukushima Daiichi Nuclear Power Plant, 3; Environmental dispersion of radioiodine: On the basis of computer simulation

Chino, Masamichi

This presentation reports re-evaluation of source term and atmospheric dispersion in the early stage of the accident based on environmental monitoring data at the Fukushima Pref. monitoring posts, pressure analysis of reactor and aerial survey data of I-131 deposition. The periods of re-evaluation are in the afternoon of March 12, 2011 when the wet venting and hydrogen explosion occurred, from the night of March 14 to the early morning of March 15 when air dose rates increased three times after the decreases of reactor core pressure and from the morning of March 15 to the mid-noon of March 16 when the largest contamination in the environment occurred. The release amounts of radioactive nuclides due to the venting of Unit 1 and the period of large amount of release in the afternoon of March 15 were cleared. The atmospheric dispersion using new source term showed better agreement with measured deposition distribution than previous one.