Nordic Boiling Water Reactors (BWRs) employ containment pressure relief and filtered venting and ex-vessel debris coolability in the deep pool located under the reactor pressure vessel as a severe accident management (SAM) strategy. Effectiveness of this strategy depends on melt release conditions from the vessel which is the major source of uncertainty in risk quantification of containment failure in Nordic BWRs in ROAAM+ Framework. In this work we focus on uncertainty analysis of vessel failure mode and melt release conditions in unmitigated station blackout accident in Nordic BWR. The timing and mode of vessel failure and melt release conditions are predicted by MELCOR code. We demonstrate the effect of MELCOR code uncertain modelling parameters and modelling options on the resultant uncertainty in vessel failure mode and melt release conditions. Results of analysis show that penetration failure is predicted to occur before creep-rupture failure of the vessel lower head, however it does not preclude eventual creep-rupture failure of the vessel lower head. The mode of debris ejection from the vessel has the dominant effect on the likelihood of creep-rupture failure of the vessel lower head and debris ejection rate from the vessel.