This paper presents a comparative and quantitative analysis of transition scenarios to potential fuel cycle options, focusing on once-through (OT) and pyro-sodium-cooled fast reactor (pyro-SFR) cycles. By employing a module-based flow diagram in system definition, we developed a dynamic mass-flow model to simulate transition scenarios in line with current Korean nuclear plans. Additionally, we derived an economic evaluation model to determine the levelized cost of electricity (LCOE) for each fuel cycle option. This model includes detailed equations for calculating reactor capital costs and the optimal concentration of depleted uranium. Our mass-flow analysis highlights the pyro-SFR cycle's superior resource utilization and reduced high-level radioactive waste (HLW) production. However, this cycle necessitates additional reactors and back-end cycle facilities. The economic evaluation reveals a marginally higher LCOE for the pyro-SFR cycle, attributed to the costs of constructing and operating these additional facilities. However, uncertainty analysis indicates that uncertainties in unit costs diminish the impact of the cost difference. Through sensitivity analysis, we identified critical modules and break-even points for unit costs, such as reactor capital and natural uranium mining. Our findings offer crucial insights for decision making in spent fuel management plans or policies. System analysis always faces challenges due to data limitations and the commercialization barriers of back-end fuel cycle technologies, however, continued efforts to enhance evaluation accuracy and reduce uncertainty is needed.