[en] Some previous assessments of the probability of containment failure caused by in-vessel steam explosions in a PWR have recognized large uncertainties and assigned broad ranges to the probability, while others have concluded that the probability is small or zero. In this report the uncertainty in the probability of containment failure is studied by combining the uncertainties in the component physical processes using a Monte Carlo method. It is concluded that, despite substantial research, the combined uncertainty is still large. Some areas are identified in which improvements in this understanding may lead to large reductions in the overall uncertainty. 49 references