Comparative Life Cycle Assessment of MOX Fast-Reactor Fuel Cycles and Exploratory REMIX-Type Recycling Scenarios Environmental Benefits of Closing the Nuclear Fuel Cycle

Closing the nuclear fuel cycle is widely recognized as a key pathway for enhancing the long-term sustainability of nuclear energy systems. This study presents a comparative life cycle assessment of three configurations: a once-through UO₂ cycle, a fast-reactor MOX closed cycle, and an exploratory REMIX-type recycled-fuel scenario. A cradle-to-grave framework is applied to quantify greenhouse gas emissions, material requirements, cumulative energy demand, high-level waste generation, and long-term radiotoxicity, with uncertainty propagation addressed through Monte Carlo simulation and global sensitivity analysis. Across all configurations, life-cycle greenhouse gas emissions remain consistently low (<20 g CO₂-eq/kWh), confirming that fuel-cycle structure does not materially alter the climate mitigation potential of nuclear electricity. In contrast, pronounced differences emerge in resource efficiency and waste management. The MOX-based fast-reactor configuration reduces natural uranium demand by approximately 50% and significantly lowers long-term radiotoxicity and high-level waste volumes relative to the once-through cycle. The REMIX-type scenario exhibits further reductions across these indicators within the adopted fuel-cycle inventory assumptions, illustrating the potential environmental implications of integrated uranium–plutonium recycling pathways. Sensitivity analysis reveals that environmental performance is primarily governed by upstream parameters, including uranium ore grade, enrichment technology, reprocessing energy demand, and the carbon intensity of fuel-cycle operations, rather than by reactor-specific variables. Importantly, the REMIX-type scenario is treated strictly as a fuel-cycle-level exploratory construct; it is not represented as a validated fast-reactor core design, and no claims are made regarding fast-reactor core feasibility, breeding ratios above unity, or isotopic equilibrium. These findings demonstrate that fuel-cycle closure, particularly through MOX-based fast-reactor systems, constitutes a technically grounded strategy for improving material efficiency and waste outcomes without compromising the low-carbon profile of nuclear energy. More broadly, the study highlights the need to integrate life cycle assessment with reactor physics, core-design, and fuel-performance analyses before advanced recycled-fuel scenarios can be interpreted as deployable reactor configurations