Core melt sequences are studied at the design stage of third generation reactors due to the high threat posed to population and environment. Phenomenological models employed in the deterministic codes for transient simulation are often based on experimental campaigns and past accidents, thus subject to uncertainty that is propagated to the code outputs. As the impact of uncertain model inputs on the evolution of system variables and key timings of a severe accident is determined, critical components can be identified and operator procedures adjusted. This task requires a large number of model runs which is often practicable only on an HPC cluster.