Updated analysis of Fukushima unit 3 with MELCOR 2.1. Part 1: Thermal-hydraulic analysis

The state of the core after 350 h seems to be in agreement with our case 2, where ca. 64 tons of debris and stainless steel structures remained in the lower head and ca. 70 tons of debris were ejected to the pedestal. Taking into account the limitation in the modelling of the failure modes of a BWR, this estimation is very uncertain. Further discussion will be provided in the second part of the paper where the fission product release and transport will be studied and compared against available source term calculations.