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A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak Configuration with Natural Uranium

A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak Configuration with Natural Uranium. Mark Reed. FUNFI Varenna, Italy September 13 th , 2011. PART I: The Issue PART II: Fission PART III: Fusion PART IV: Conclusions. PART I: The Issue. Why this might be a good idea.

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A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak Configuration with Natural Uranium

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  1. A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak Configuration with Natural Uranium Mark Reed FUNFI Varenna, Italy September 13th, 2011

  2. PART I: The Issue • PART II: Fission • PART III: Fusion • PART IV: Conclusions

  3. PART I: The Issue Why this might be a good idea

  4. Contention Fission-fusion hybrids could actually be more viable than stand-alone fusion reactors and obviate some challenges of fission.

  5. Constraints • D-T tokamaks • Fully non-inductive (steady-state) • Low confinement mode (L-mode) operation • Pebble bed blanket with helium coolant • Natural or depleted uranium • Lithium-lead eutectic layer for tritium breeding (one triton per fusion neutron)

  6. PART II: Fission The maximum natural uranium blanket power gain

  7. Basic Layout natural uranium with He coolant Li-Pb shield

  8. Neutronics Methodology • Developed a subcritical Monte Carlo code (benchmarked with MCNP) • Treated uranium and lithium layers as elongated toroidal shells (quartic solutions for neutron path lengths) • ENDF cross-sections and other nuclear data

  9. Blanket Variables • Uranium toroidal layer thickness • Lithium toroidal layer thickness • Relative positioning of toroidal layers • Homogenized uranium density (different pebble designs) • Lithium enrichment • Major and minor tokamak radii

  10. Layer Thickness Optimization

  11. Subcritical Neutron Multiplication k0 = 1.19 k = 0.27

  12. Total Power Composition

  13. Fusion-Born Neutron Fate

  14. Fission Results • Blanket power gain of 7 • Tritium breeding ratio of 1.05 • Uranium layer thickness of 18 cm • Lithium enrichment of 90% 6Li • Helium coolant velocity ≈ 10 m/s

  15. PART III: Fusion The minimum tokamak size for steady-state L-mode operation

  16. 0-D Tokamak Model • Volume-averaged parameters • Simply relate R, a, B, q*, Pfus, and Qfus • Current limit and safety factor (q* > 2) • Greenwald density limit • Troyon no-wall pressure limit (βN < 3) • L-mode operation (H-89 scaling) • Fully non-inductive (fNI ≈ 1) • Solenoid flux approximately twice plasma flux

  17. Fusion power surface density PF/AS and fixed Bmax uniquely define each operating point 2 < R/a < 4 0-D Tokamak Relations 4 1 2 5 6 3

  18. Stand-Alone Fusion Reactor Q = 40, R/a = 2.6, Bmax = 15 T, PF/AS = 5 MW/m2.

  19. Fission-Fusion Hybrid Reactor Q = 6.3, R/a = 3.1, Bmax = 15 T, PF/AS = 3 MW/m2.

  20. Fusion Results • Major radius of 5.2 m • Aspect ratio of 2.8 • Maximum on-coil magnetic field of 15 T • Fusion gain of 6.7 • Total fusion power of 1.7 GW • Safety factor of 3.0 • H89 = 1.48 (L-mode)

  21. PART IV: Conclusions What this all means

  22. Fission-Fusion Advantages • Fully non-inductive L-mode operation at small scale (low capital cost relative to pure fusion devices) • Subcritical operation (flexibility and safety) • Control of fission blanket indirectly through control of the tokamak plasma – fission blanket gain increases with time due to plutonium breeding • No uranium enrichment (non-proliferation) • Enhanced transmutation of long-lived fission products through (n,2n) reactions

  23. Conclusion Instead of complicating the already difficult challenges of fission and fusion, fission-fusion hybrids could actually simplify many difficult aspects of fission and fusion. A profusion of pro-fusion sentiment?

  24. Acknowledgements Prof. Ron Parker (fusion) Prof. Ben Forget (fission) MIT Plasma Science and Fusion Center (PSFC) report: M. Reed, R. Parker, B. Forget. “A Fission-Fusion Hybrid Reactor in L-Mode Tokamak Configuration with Natural Uranium”. PSFC/RR-11-1 (2011).

  25. Extra Slides

  26. L-mode and H-mode • H-mode has rough profiles that create edge-localized modes (ELMs), the bane of current fusion research. • L-mode does not give rise to ELMs but has lower power density. • Some current hybrid designs are based on ITER (H-mode).

  27. Hybrid Power The fission blanket augments the fusion power.

  28. At large size, increases in temperature lead to operation at the maximum D-T rate coefficient. T near <σv> maximum provides inherent stability (negative reactivity coefficient) Absolute <σv> maximum limits feasible parameter space 66 keV Log (D-T rate coefficient) T= 10 keV 100keV

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