Level 2 probabilistic risk assessments of nuclear plants (analysis of radionuclide release from containment) may require hundreds of runs of severe accident analysis codes such as MELCOR or RELAP/SCDAP to analyze possible sequences of events (scenarios) that may follow given initiating events. With the advances in computer architectures and ubiquitous networking, it is now possible to utilize multiple computing and storage resources for such computational experiments. This paper presents a system software infrastructure that supports execution and analysis of multiple dynamic event-tree simulations on distributed environments. The infrastructure allow for 1) the testing of event tree completeness, and, 2) the assessment and propagation of uncertainty on the plant state in the quantification of event trees