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 fl ow diagram in

system defi nition, we developed a dynamic mass-fl ow model to simulate transition scenarios in line with the 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-fl ow 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 diff erence. Through sensitivity analysis, we identifi ed critical modules and break-even

points for unit costs, such as reactor capital and natural uranium mining. Our fi ndings off er crucial insights for decisionmaking

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 eff orts to enhance evaluation accuracy

and reduce uncertainty are needed.