Updated analysis of Fukushima Unit 3 with MELCOR 2.1. Part 2: Fission product release and transport analysis

The fission product release and transport during the accident of Fukushima Daiichi Unit 3 was analysed in the present paper as a complement to the thermal-hydraulic analysis presented in the first part of the present study, where three sequences obtained with MELCOR 2.1. were evaluated. The calculation results were compared against the available data for fission products: i) dose rate measurements in the containment drywell and suppression chamber, ii) the environmental release data by reverse calculations performed with WSPEEDI-II, and iii) estimations of water releases to the turbine and reactor buildings. From the fission product analysis perspective, the best results were obtained with case 2 sequence, further confirming the results obtained in the first part of the analysis. However, the comparison of the analysis results with the dose rate measurements in the drywell indicates that the reactor pressure vessel failure took place 2 h earlier than predicted in the case 2, i.e., at ca. 62 h after scram.