Comparative Life Cycle Assessment of MOX and REMIX Fuels in Fast Reactors: Environmental Benefits of Closing the Nuclear Fuel Cycle

FR26: International Conference on Fast Reactors and Related Fuel Cycles Abstract ID : 104 Comparative Life Cycle Assessment of MOX and REMIX Fuels in Fast Reactors: Environmental Benefits of Closing the Nuclear Fuel Cycle Content The transition toward sustainable nuclear energy systems requires optimizing the nuclear fuel cycle to minimize environmental burdens and maximize resource utilization. Conventional once-through light water reactors (LWRs) utilize less than 1% of the total energy potential of natural uranium, as only a small portion of U-235 and some plutonium bred from U-238 are fissioned before discharge. In contrast, fast reactors (FRs) operating under closed fuel cycles with mixed oxide (MOX) or regenerated mixture (REMIX) fuels can enhance uranium utilization, reduce long-term radiotoxicity, and contribute to decarbonization objectives aligned with the IAEA’s Atoms4NetZero initiative. A comparative life cycle assessment (LCA) was performed for three representative fuel cycles: (1) open oncethrough UO₂, (2) fast reactor single-recycle MOX, and (3) fast reactor multi-recycle REMIX. The system boundaries and methodological assumptions are summarized in Table 1, which includes reactor type, fuel composition, burn-up, breeding ratio, reprocessing losses, and electricity mix. The LCA followed ISO 14040/44 standards and used IAEA, OECD/NEA, and ORNL datasets. Environmental performance was assessed through six indicators: Global Warming Potential (GWP₁₀₀), uranium requirement, HLW volume, radiotoxicity at 1000 years, minor actinide inventory, and Cumulative Energy Demand (CED). As presented in Table 2, both MOX and REMIX cycles show substantial environmental advantages over the once-through cycle. The MOX cycle reduces uranium demand by ~30% and HLW volume by 35%, while lowering radiotoxicity by 60%. The REMIX configuration achieves up to 55% reduction in uranium demand, 45% less HLW, and 70% lower radiotoxicity. Minor actinide generation also declines, reducing repository burden. Only GWP₁₀₀ shows a moderate increase (5–10%), caused by the carbon intensity of current reprocessing. When modeled under a low-carbon energy scenario—where reprocessing uses nuclear or renewable electricity —the GWP₁₀₀ of closed cycles decreases by 10–20% relative to the open cycle. Under these conditions, total life-cycle emissions fall below 10 g CO₂-eq/kWh, keeping nuclear power among the lowest-carbon energy options. The CED remains within 10% of the baseline, offset by avoided uranium mining and enrichment. These results confirm that the main environmental advantage of fast reactor fuel cycles lies not in immediate CO₂ reduction but in long-term resource efficiency and waste minimization. Tables 1 and 2 illustrate that closed cycles are key to a sustainable and resource-efficient nuclear future. Tables 1 and 2 Country/Int. organization Colombia Author: Prof. PRIETO VALDERRAMA, Camilo (Pontificia Universidad Javeriana (Colombia)) Co-author: Prof. PATIÑO, Diego (Pontificia Universidad Javeriana) Presenter: Prof. PRIETO VALDERRAMA, Camilo (Pontificia Universidad Javeriana (Colombia)) Track Classification: 4. NFC - Track 3. Fuel Cycle Technologies and Sustainability Contribution Type: ORAL Submitted by Prof. PRIETO VALDERRAMA, Camilo <[email protected]> on Monday 13 October 2025 Last modified: Monday 13 October 2025