[en] The insertion of a new concept (fuel, reactor, process) must be evaluated in the global electronuclear system with an analysis of the impact on the fuel cycle (Enrichment, Fuel Fabrication, Reactor, Processing, Interim Storage, Waste storage). An approach of scenario studies is used to evaluate different solutions to manage nuclear materials (uranium, plutonium) and wastes (minor actinides and fission products), from the present situation (partially closed cycle) until the total closed cycle with GEN IV systems, in calculating the fluxes and the inventories of these elements in each step of the fuel cycle and to treat the transient period to pass from one situation to the others. For some interesting scenarios, the approach consists on a simulation of transient scenarios from the present situation to the equilibrium situation with a COSI code. The results given at each point of the fuel cycle and for each year permit to demonstrate the technological feasibility and to evaluate the impacts on environmental, economical, proliferation and waste storage aspects. After a presentation of the operational approach, this paper gives an example for a French transient scenario between the present situation and the end of the 21. century with the introduction of GEN IV fast reactors. The results presented in this paper give the impacts on: - The natural uranium resources, - The capacity of different plants (enrichment, fabrication, reprocessing) and interim storages for spent fuels, - The inventory, function of time, of different elements (Pu, Np, Am, Cm) at each stage of the fuel cycle and in the wastes, - The thermal power the high level wastes. (authors)