A Fukushima Daiichi Unit 3 MELCOR model from Technical Research Centre of Finland (VTT) was modified to simulate the Fukushima Daiichi Unit 2 accident. Several simulations were performed using three different modeling approaches. The base model (1F2 v1) includes only the basic modifications to reproduce the accident. The intermediate model (1F2 v2) includes an improved model of the Wet Well. In the advanced model (1F2 v3), the reactor core isolation cooling system logic was modified to avoid the use of tabular functions for the mass flow inlet and outlet. As a result of this analysis it is concluded that there is a strong dependency on parameters which still have many uncertainties, such as the reactor core isolation cooling system two-phase flow operation, the alternative water injection, the suppression pool behavior, the rupture disk behavior and the containment failure modes which affect the final state of the reactor core.

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