Keywords:Fukushima Daiichi Nuclear Power Plants, Severe Accident, Meltdown, SAMPSON
The accident at the Fukushima Daiichi unit 3 has been studied extensively in the last years but still wide uncertainty exists on the employment of the operative systems. Such uncertainties reflect on the onset and progression of the core melting. In the present analysis the SAMPSON code has been applied to the whole accident in order to identify and discuss such uncertainties. The results have shown that the core melt will progress after ADS depressurization and that around 40% of the core will relocate. Such relocation is responsible for the RPV failure and transfer of the fuel debris into the pedestal.