Keywords:Fukushima Daiichi Nuclear Power Plants, Severe Accident, 3 weeks analysis, SAMPSON
As participant in the project aimed at improving the understanding of Fukushima Daiichi (1F) NPP conditions, IAE has performed a comprehensive evaluation and analyses of the 1F units. At the beginning the accident scenario has been evaluated deeply among all the members of the project, subsequently the SAMPSON code has been applied to confirm assumed phenomena and clarify uncertain points. The analysis has confirmed that at Unit 3 a large portion of the core melted and relocated in the lower plenum. Thereafter, because of lack of cooling, RPV failed and subsequently debris was gradually transferred to the pedestal triggering the MCCI. It is estimated that a little amount of debris might have remained in the lower plenum while a considerable portion relocated to the pedestal with limited spread to the DW.