This paper focuses on the development of a conceptual framework for integrating fault injection mechanisms into the RDD-100 tool to support the dependability analysis of computer systems early in the design process. The proposed framework combines functional and behavioral modeling, fault injection and simulation. Starting from the RDD-100 model built by the system designers, two techniques are discussed for the mutation of this model to analyze its behavior under faulty conditions: a) insertion of saboteurs into the model, and b) modification of existing component descriptions. Four types of fault models are distinguished and specific mechanisms to simulate the corresponding fault models are proposed for each mutation technique. An approach combining the advantages of both techniques is proposed and a prototype implementing this approach is briefly described.