Uncertainty analyses using the Melcor severe accident analysis code

The MELCOR code is a detailed system level computer code capable of performing integrated self-consistent analyses of severe accident progression in commercial nuclear power plants, supporting level 2 probabilistic risk assessment (PRA) studies. Originally developed as a fast running tool with simplified models for performing probabilistic safety analyses and sensitivity studies, MELCOR now employs largely best estimate models for severe accident phenomena while retaining rich capabilities for performing sensitivity and uncertainty analysis. Extensive user access to fundamental coefficients and parameters of MELCOR underlying physics models combined with the advent of fast and increasingly economical computing power has enabled complex system models like MELCOR to be applied to uncertainty analyses such as those performed using Monte Carlo and Latin Hypercube Sampling (LHS) methods. This paper illustrates two such recent applications of MELCOR 1.8.5 to the uncertainty analysis of hydrogen production and of containment aerosol behavior in severe reactor accidents. The examples illustrated in this paper show both the application of LHS to accommodate computationally intensive accident models and a Monte Carlo analysis involving larger sample size for less computationally intensive analyses to attain better sampling statistics. (author)