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[en] The research described in this report was performed under a grant from the U.S. Department of Energy (DOE) to describe and compare the merits of two advanced alternative nuclear fuel cycles -- named by this study as the 'UREX+3c fuel cycle' and the 'Alternative Fuel Cycle' (AFC). Both fuel cycles were assumed to support 100 1,000 MWe light water reactor (LWR) nuclear power plants operating over the period 2020 through 2100, and the fast reactors (FRs) necessary to burn the plutonium and minor actinides generated by the LWRs. Reprocessing in both fuel cycles is assumed to be based on the UREX+3c process reported in earlier work by the DOE. Conceptually, the UREX+3c process provides nearly complete separation of the various components of spent nuclear fuel in order to enable recycle of reusable nuclear materials, and the storage, conversion, transmutation and/or disposal of other recovered components. Output of the process contains substantially all of the plutonium, which is recovered as a 5:1 uranium/plutonium mixture, in order to discourage plutonium diversion. Mixed oxide (MOX) fuel for recycle in LWRs is made using this 5:1 U/Pu mixture plus appropriate makeup uranium. A second process output contains all of the recovered uranium except the uranium in the 5:1 U/Pu mixture. The several other process outputs are various waste streams, including a stream of minor actinides that are stored until they are consumed in future FRs. For this study, the UREX+3c fuel cycle is assumed to recycle only the 5:1 U/Pu mixture to be used in LWR MOX fuel and to use depleted uranium (tails) for the makeup uranium. This fuel cycle is assumed not to use the recovered uranium output stream but to discard it instead. On the other hand, the AFC is assumed to recycle both the 5:1 U/Pu mixture and all of the recovered uranium. In this case, the recovered uranium is reenriched with the level of enrichment being determined by the amount of recovered plutonium and the combined amount of the resulting MOX. The study considered two sub-cases within each of the two fuel cycles in which the uranium and plutonium from the first generation of MOX spent fuel (i) would not be recycled to produce a second generation of MOX for use in LWRs or (ii) would be recycled to produce a second generation of MOX fuel for use in LWRs. The study also investigated the effects of recycling MOX spent fuel multiple times in LWRs. The study assumed that both fuel cycles would store and then reprocess spent MOX fuel that is not recycled to produce a next generation of LWR MOX fuel and would use the recovered products to produce FR fuel. The study further assumed that FRs would begin to be brought on-line in 2043, eleven years after recycle begins in LWRs, when products from 5-year cooled spent MOX fuel would be available. Fuel for the FRs would be made using the uranium, plutonium, and minor actinides recovered from MOX. For the cases where LWR fuel was assumed to be recycled one time, the 1st generation of MOX spent fuel was used to provide nuclear materials for production of FR fuel. For the cases where the LWR fuel was assumed to be recycled two times, the 2nd generation of MOX spent fuel was used to provide nuclear materials for production of FR fuel. The number of FRs in operation was assumed to increase in successive years until the rate that actinides were recovered from permanently discharged spent MOX fuel equaled the rate the actinides were consumed by the operating fleet of FRs. To compare the two fuel cycles, the study analyzed recycle of nuclear fuel in LWRs and FRs and determined the radiological characteristics of irradiated nuclear fuel, nuclear waste products, and recycle nuclear fuels. It also developed a model to simulate the flows of nuclear materials that could occur in the two advanced nuclear fuel cycles over 81 years beginning in 2020 and ending in 2100. Simulations projected the flows of uranium, plutonium, and minor actinides as these nuclear fuel materials were produced and consumed in a fleet of 100 1,000 MWe LWRs and in FRs. The model also included recycle and reuse of extant inventories of spent LWR fuel. The results of the simulations allowed comparisons of the two fuel cycles from the standpoints of cost, non-proliferation, radiological health, wastes generated, and sustainability. Results of the research also provide insights regarding (i) multiple recycling of uranium and plutonium from spent MOX fuel in LWRs, (ii) costs and benefits of reenriching and reusing uranium from spent LWR fuel; (iii) effects of using uranium, plutonium, and minor actinides from LWR spent fuels to produce fuel for FRs; (iv) net rates of consumption (burning) in FRs of actinide elements produced in LWRs, and (v) ependencies of and interactions among the different systems of an advanced nuclear fuel cycle -- and the flows of nuclear materials between these systems.