[en] Sensitivity analyses for the in-vessel combustible gas generation, using the MELCOR program, are described in this report for the APR1400. The typical accident sequences of a station blackout and a large LOCA scenario are selected. A lower head failure model, a Zircaloy oxidation reaction model and a B₄C reaction model are considered for the sensitivity parameters. As for the base case, 1273.15K for a failure temperature of the penetrations or the lower head, an Urbanic-Heidrich correlation for the Zircaloy oxidation reaction model and the B4C reaction model are used. Case 1 used 1650K as the failure temperature for the penetrations and Case 2 considered creep rupture instead of penetration failure. Case 3 used a MATPRO-EG and G correlation for the Zircaloy oxidation reaction model and Case 4 turned off the B₄C reaction model. The results of the studies are summarized below : (1) Both the higher penetration failure temperature and the creep rupture failure model cause a large amount of hydrogen generation for a station blackout sequence. For a large LOCA, however, the hydrogen generation doesn't change much. (2) The MATPRO-EG and G correlation for a Zircaloy oxidation reaction results in less hydrogen generation than the Urbanic-Heidrich correlation (Base case) for both scenarios. (3) When the B₄C reaction model turns off, the amount of hydrogen decreases for two sequences. (4) The amount of CO, CO₂, and CH₄ do not significantly change for two sequences. It is found that the selection of hydrogen generation model affects fuel relocation characteristics inside the core include fuel channel blockage. Since it changes the amount of hydrogen generated from the core, a future study is recommended on this area