The effects of a total loss of power with station blackout and subsequent core meltdown for the model of boiling water reactor were simulated by using specialized computer program. The simulation included the processes running inside the reactor core as well as inside cooling systems and containment. The anal. was focused on the mechanisms of non-condensable gas generation (H-2, CO, CO, MeH) and steam prodn., which created the highest threat of damage of the reactor containment.