Abstract: Independent analyses by the present author on Fukushima accident are introduced. The analyses have been performed of the core melt behavior of the Unit 1, Unit 2 and Unit 3 reactors of Fukushima Daiichi Nuclear Power Station on March 11^th-15^th, 2011. The analyses are based on a phenomenological methodology with measured data investigation and a simple physical model calculation. Estimated are time variation of core water level, core material temperature and hydrogen generation rate. The analyses have revealed characteristics of accident process of each reactor. In the case of Unit 2 reactor, the calculated result suggests little hydrogen generation because of no steam generation in the core for zirconium-steam reaction during fuel damage process. It could be the reason of no hydrogen explosion in the Unit 2 reactor building. Analyses have been performed also on the core material behavior in another chaotic period of March 19^th-31^th, 2011, and it resulted in a re-melt hypothesis that core material in each reactor should have melted again due to shortage of cooling water. The hypothesis is consistent with many observed features of radioactive materials dispersion into the environment. The analyses show validity and importance of independent analyses based on simple physical model calculation.  

Keyword: Fukushima Daiichi accident; core melt; re-melt; simple physical model