Analysis of the accident in the Fukushima Daiichi nuclear power station Unit 3 with MELCOR_2.1

In the present paper, the Fukushima Unit 3 accident has been studied by using Melcor_2.1. An initial calculation was performed by using design conditions or operators reported actions. Several series of sensitivity cases have been performed in order to reproduce the main accident measurements (e.g. pressure histories of the reactor pressure vessel, dry-well and wet-well; downcomer water levels and the observed hydrogen explosion time). The sensitivity studies consisted in variations of Reactor Core Isolation Cooling and High Pressure Coolant Injection operation, Alternative Water Injection, venting, leaking to the dry-well and failure parameters of the lower head. The outcomes of the sensitivity calculations have pointed out the likely-state of the U3 core after 6 days of the accident start.