Fuel Cycle Subcommittee: Overview and Status

1. Fuel Cycle Subcommittee:Overview and Status Fusion-Fission Hybrid Workshop Gaithersburg, MD September 30, 2009 Robert N. Hill Department Head – Nuclear Systems Analysis Nuclear Engineering Division Argonne National Laboratory Work sponsored by U.S. Department of Energy Office of Nuclear Energy, Science & Technology

2. Overview • A wide variety of hybrid concepts are proposed • Different fuel cycle missions are postulated • Thus, it is important to provide a systematic and well defined framework to categorize • Goals of different fuel cycle approaches • Strategies employed to meet the fuel cycle goals • This is a prerequisite for valid comparisons • (e.g., a breeder compared to a minor actinide burner should have vastly different performance)

3. Outline of Fuel Cycle Chapter • 3.1 Fission Fuel Cycles • 3.2 Fusion Fuel Cycles • 3.3 Proposed Hybrid Fuel Cycles • Limited input on 3.3 before workshop! Given that fusion-fission hybrids primarily conceived to deal with fission fuel cycle issues, the focus of this presentation will be on 3.1

4. 3.1 Fission Fuel Cycles • Nuclear energy is a significant contributor to U.S. and international electricity production • 16% world, 20% U.S., 78% France • Given the concern over carbon emissions, there may be significant growth worldwide • In the U.S., a once-through fuel cycle has been employed to-date • Large quantities of spent fuel stored at reactor sites • Final waste disposal is not secured • With nuclear expansion, this is not a sustainable approach; thus, advanced fuel cycles being explored – two key goals • Waste Management • Resource Utilization

5. AFCI is considering a variety of fuel cycle options: Closed fuel cycle with actinide management Energy Production Reactor • Spent nuclear fuel will be separated into re- useable and waste materials • Residual waste will go to a geological repository • Uranium recycled for resource extension • Fuel fabricated from recycled actinides used in recycle reactor • Fuel cycle closure with repeated use in recycle reactor Extend Uranium Resources Recycle Used Uranium Recycle Reactor Recycle Fuel Fabrication

6. Advanced Nuclear Fuel Cycle – Potential Benefits • Reduction in the volume of HLW that must be disposed in a deep geologic disposal facility as compared to the direct disposal of spent nuclear fuel • Factor of 2-5 reduction in volume as compared to spent nuclear fuel • Intermediate-level (GTCC) and low-level volumes could be large and disposal pathways would have to be developed • Reduction in the amount of long-lived radioactive material (e.g., minor actinides) that must be isolated in a geologic disposal facility (reduction of source term) • Potential for re-design of engineered barriers • Advanced waste forms could result in improved performance and reduced uncertainty over the very long time periods • Reduction in decay heat allowing for increased thermal management flexibility, potentially increasing emplacement density • Increased loading density - better utilization of valuable repository space

7. Waste Hazard and Risk Measures • Radiotoxicity reflects the hazard of the source materials • transuranics dominate after about a 100 years. The fission products contribution to the radiotoxicity is small after 100 years • Radiotoxicity alone does not provide any indication of how a geologic repository may perform • Engineered and natural barriers serve to isolate the wastes or control the release of radionuclides

8. Transmutation for Improved Waste Management • Long-term heat, radiotoxicity, and peak dose are all dominated by the Pu-241 to Am-241 to Np-237 decay chain • Thus, destruction of the transuranics (neptunium, plutonium, americium, and curium) is targeted to eliminate all problematic isotopes • Some form of reprocessing is necessary to extract transuranic elements for consumption elsewhere • The transuranic (TRU) inventory is reduced by fission • Commonly referred to as ‘actinide burning’ • Transmutation by neutron irradiation • Additional fission products are produced • This requires the development of transmutation fuel forms • Robust fast reactor fuel form – high reliability • Partial destruction each recycle – high burnup goal • In the interim, the TRU inventory is contained in the transmutation fuel cycle

9. Reactor Types for Transmutation System:Minimization of Waste • Conventional LWRs using LEU fuels produce TRU • At current 50 GWd/MT burnup, 1.3% TRU content at discharge • This corresponds to ~250 kg/year for each GWe power • For any fission energy system, 1 gram of actinides destroyed produces roughly 1 MWt-day of energy • This implies 1.3%/5% = 25% of the original LWR energy production is created in the destruction of the TRU content (significant capacity) • Thus, efficient use of this energy is a key to both system economics and resource utilization • However for uranium-based fuel, TRUs are also being produced • This behavior is quantified by the conversion ratio (CR) • Dictated primarily by the recycle fuel composition (U content) • Fast system can be designed with CR ranging from >1 (breeders) to <<1 (burners); for thermal reactors CR < 0.7 is achievable with MOX

10. Reactor Types for Transmutation System:Minimization of Waste (cont.) • To assure no TRUs remain in waste, the LWR production rate must be balanced by destruction in the actinide burners (AB) • For pure burner (CR=0), 1 burner for every four LWRs • For CR=0.25, 1 burner for every three LWRs • For CR=1, all recycle reactors • If only the minor actinides are to be consumed in the burner reactor, the initial production rate by LWRs is only 10% of the TRU content • However, the plutonium must be consumed elsewhere • Additional minor actinides are produced as the plutonium is consumed, particularly if a thermal spectrum is utilized

11. Reactor Types for Transmutation System:Maximization of Energy • The opposite trend is observed when the goal is to maximize the energy production for a fixed amount of resource materials • For a given quantity of recovered TRU, the energy can be extended by recycling the material in a high CR system • Thus, net resource utilization is vastly improved at high CR • For once-through cycle, 7MT of uranium ore required to produce 1 MT of fuel to 5% burnup -- .05/7 = 0.7% of the energy content • With TRU recovery and recycle, burnup extended to .05 + .013/(1-CR) • Roughly 1% of energy content at low conversion ratio • Limit of 100% utilization at CR=1 where a make-up feed (e.g., depleted uranium or thorium) that contains fertile material is required

12. 3.2 Fusion Fuel Cycles • Tritium needs to be produced to sustain the fusion cycle • 14 MeV neutrons can be used to breed • Typically employ Li-6 capture in fusion blanket • For hybrid, fusion blanket must also be utilized • Wide variety of technology options • Homogeneous or heterogeneous with fission blanket • Neutron balance is enhanced through subcritical multiplication in the fission blanket

13. 3.x.4 Proliferation Issues • The proliferation risks associated with spent fuel reprocessing and recycle continue to be hotly debated • At least partial separation is required • Fission products are waste, actinides recycled • This reduces the radiation barrier • Safeguards employed for material accounting • Physical protection provides additional barriers • Technology misuse is another concern • Enrichment technology may be an easier pathway • Any neutron source can produce fissile material • Fertile targets installed to capture neutrons • This became an issue for ADS concepts

14. 3.3 Hybrid Fuel Cycles • Waste management role • Lack of criticality constraint allows operation on very low reactivity fuels and potentially very high burnup • However, practical operation (e.g., large power swings) and material (e.g., radiation damage) challenges exist • Some proposals: • Burn the entire TRU inventory • Target a smaller fleet of minor actinide burners • Sustain “support” of LWR power production or nuclear close-out scenarios (like ADS) • Resource extension role proposals: • Breed fuel for use in fission fuel cycle • Perform an extended in-situ breed and burn • Similar challenges to the burner mode noted above

15. Backup Slides

16. Fast and Thermal Reactor Energy Spectra • In LWR, most fissions occur in the 0.1 eV thermal “peak” • In SFR, moderation is avoided – no thermal neutrons

17. Impact of Energy Spectrum on Fuel Cycle (Transmutation) Performance • Fissile isotopes are likely to fission in both thermal/fast spectrum • Fission fraction is higher in fast spectrum • Significant (up to 50%) fission of fertile isotopes in fast spectrum Net result is more excess neutrons and less higher actinide generation in FR

18. Equilibrium Composition in Fast and Thermal Spectra • Equilibrium higher actinide content much lower in fast spectrum system • Generation of Pu-241 (key waste decay chain) is suppressed • However, if starting from once-through LWR composition (e.g., burner reactor) the higher actinide content will be higher than the U-238 equilibrium

19. Fuel Cycle Implications The physics distinctions facilitate different fuel cycle strategies • Thermal reactors are typically configured for once-through (open) fuel cycle • They can operate on low enriched uranium (LEU) • They require an external fissile feed (neutron balance) • Higher actinides must be managed to allow recycle • Separation of higher elements – still a disposal issue • Extended cooling time for curium decay • Fast reactors are typically intended for closed fuel cycle with uranium conversion and resource extension • Higher actinide generation is suppressed • Neutron balance is favorable for recycled TRU • No external fissile material is required • Can enhance U-238 conversion for traditional breeding • Can limit U-238 conversion for burning

20. Advanced Nuclear Fuel Cycle – Potential Benefits • Cs/Sr (and decay products), Cm, and Pu dominate “early” decay heat • Am dominates “later” decay heat • Removal of decay heat producers would allow for increased utilization of repository space

21. Aqueous Processing Potential Waste Streams and Waste Forms Cladding: Zircaloy Hardware: SS Chopping Metal Waste Form Volox Specialized Waste Forms Gases: I, HTO, Kr, Xe, CO2 Dissolu-tion Metal Waste Form UDS: Pd, Ru, Rh, Mo, Tc, Zr, O Tc Metal Waste Form Ion Exchange UREX U Decay Storage Waste Form (glass or ceramic) FPEX Cs/Sr: Cs, Sr, Ba, Rb Metal Waste Form TRUEX TMFP: Fe, S, Ru, Pd, Rh, Mo, Zr Glass Waste Form LNFP: Ce, Ln, Pr, Nd, Y TALSPEAK Losses TRU: Pu, Am, Cm, Np

22. Advanced Nuclear Fuel Cycle – Waste Form Development Cs/Sr Glass Glass Bonded Sodalite Metallic Waste Form from Electro-Chemical Processing Lanthanide Borosilicate Glass

23. Advanced Nuclear Fuel Cycle - Waste Management • Waste management is an important factor in developing and implementing an advanced closed nuclear fuel cycle • The waste management system is broader than disposal (processing, storage, transportation, disposal) • Deep geologic disposal will still be required • Disposal of low level and intermediate level (GTCC) wastes will be required • Volumes potentially larger than once-through • An advanced closed nuclear fuel cycle would allow for a re-optimization of the back-end of the current once-through fuel cycle, taking advantage of: • Minor actinide separation/transmutation • Heat producing fission product (Cs/Sr) management (i.e., decay storage) • Decisions must consider this entire system • Regulatory, economic, risk/safety, environmental, other considerations

24. Waste Management System for Advanced Fuel Cycle • AFCI Integrated Waste Management Strategy establishes the framework for analyzing and optimizing the waste management system • Emphasizes recycle and reuse, but based on economic recovery evaluation factoring in value of material and cost avoidance of disposal • Considers need for industry to have a reliable system to routinely transport nuclear materials and dispose wastes • Considers disposal options based on the risk of the waste streams and waste forms • Rather than requiring all waste be disposed as HLW in a geologic repository • Requires change to existing waste classification system embodied in current regulatory framework • A key aspect is the inclusion of managed storage facilities where isotopic concentrations, and heat, are allowed to decay prior to storage • Evaluation of alternatives and options are being performed under the context of the IWMS

25. Integrated Waste Management Strategy – Logic Diagram