FuzzyFTA: a fuzzy fault tree system for uncertainty analysis. This paper describes a new approach and new computational system, FuzzyFTA, for reliability analysis using fault tree and fuzzy logic. Some measures are defined to determine critical components and the uncertainty contribution of each one to the system. The FuzzyFTA system includes algorithms to consider the minimal cut set approach for the top event calculation. After that, these algorithms are used to determine importance measures. The computer code application is the Auxiliary Feedwater System (AFWS) analysis, a recent study made for Angra-I, Brazilian NPP.