A dynamic simulation model, named NUCYCLE, for nuclear fuel cycle systems was developed to analyze the lifecycle environmental impact of complex combinations of various fuel cycle processes and reactor types. The dynamic mass flow analysis capability of the developed model was verified against the OECD/NEA benchmark scenarios. The results of the open fuel cycle in this model are in close agreement with other models. As the complexity of fuel cycle systems increases with multiple recycling, the developed model produces results that are slightly different from other models, but the overall trends observed in the model are similar to those of other models for all the benchmark scenarios. The model was also applied to assess the environmental impact of three nuclear fuel cycle transition scenarios used for the verification study. The life cycle assessment estimates the remaining stockpile of high level waste and the accumulated emission of CO2 ranged 3-4 gCO(2)/kWh. Full recycling has the lowest CO2 emission because of reduced activities in uranium mining, conversion, and enrichment. (C) 2016 Elsevier Ltd. All rights reserved.