A transition fuel cycle analysis was performed fromstart-up using low enriched uranium (LEU) to a selfsustainingequilibrium core recycling all uranium andtransuranics in a fast reactor fleet. Because there are somany valid approaches based on variations andassumptions of design goals and safety and regulatoryrequirements, this is not presenting results of specificanalyses performed, but informing on the understandingof the general behavior, potential benefits, and issues andchallenges for the use of LEU for initial deployment of afleet of commercial reactors. This required a range ofdesign approaches to be considered, a number of reactorconcepts were analyzed, a point core model was utilizedto assess the basic nuclear physics and neutron balance,along with idealize spreadsheet transition models, anddetail dynamic system models of the fuel cycle transition.This is necessary to understand and inform on the manyconsiderations important for understanding behaviorform LEU start-up to self-sustaining equilibrium fastreactor fleet under the broad range of possible futures.A good qualitative understanding was developed anddescribed, along with a grasp of the potential issues andchallenges associated with the primary designalternatives envisioned. The use of LEU in fast reactorswill result in a significant increase in demand for naturaluranium and enrichment over light-water reactors(LWRs) because of the higher enrichments. The averagecomposition of the recycle fuel will vary significantly overtransition which will take many recycles (decades) toapproach steady state. The recycle material will be muchless radiologically challenging than that recycled fromLWRs, which will delay (assuming the LWR fuel iseventually recycled) the need for remote fabrication if theminor actinides are recycled. The investment in allrecycle technologies can be delayed until the FRs havebeen demonstrated and expand such that sufficientdemand exists to justify the large capital investmentrequired for reprocessing and fabrication of recycled fuel.
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