AbstractA synthesized methodology of safety analysis and evaluation for fusion systems has been developed to concretely assess the adaptability of fusion systems to the environment from the earliest stages of system development. The methodology objective was to summarize both the safety design requirements and achieve rational safety in fusion systems. The framework of the methodology was constructed to clarify its logical consistency. The safety characteristics of fusion systems were then investigated in detail paying attention primarily to potential hazards, so that a fusion system was identified as a distributed system in regard to energy sources and radioactive materials. Based on this recognition, a General Descriptive Model (GDM) of a fusion system has been constructed which is a highly generalized and integrated expression. The safety ensuring principle, on the other hand, set up items to be protected and categorized events for a fusion system. The development of the safety ensuring principle was a key to the practical performance of safety analysis and its evaluation in a general fusion system. Finally, by using the Function-Based Safety Analysis (FBSA) on the GDM, abnormal events were summarized into 16 typical events, according to the safety ensuring principle. Consequently, 20 design based events for the general fusion system were selected to envelope all credible abnormal events.