a fission-fusion hybrid reactor in steady-state l-mode tokamak configuration with natural uranium
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
A Fission-Fusion Hybrid Reactor in Steady-State L-Mode Tokamak
Configuration with Natural Uranium
Mark Reed
FUNFI
Varenna, Italy
September 13th, 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
Contention
Fission-fusion hybrids could actually be more viable than stand-alone fusion reactors and
obviate some challenges of fission.
€
Qhybrid = Q fus
1
5+
4
5Q fis
⎛
⎝ ⎜
⎞
⎠ ⎟
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)
PART II: Fission
The maximum natural uranium blanket power gain
Basic Layout
Li-Pb
natural uranium with He coolant
shield
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
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
Layer Thickness Optimization
Subcritical Neutron Multiplication
k = 0.27
k0 = 1.19
Total Power Composition
Fusion-Born Neutron Fate
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
PART III: Fusion
The minimum tokamak size for steady-state L-mode operation
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
Fusion power surface density PF/AS and fixed Bmax uniquely define each operating point
€
q ~Ba2 1+ κ 2
( )
RIP
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PAUX + Pα = PLOSS
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PAUX +n2
4⟨σ DTv⟩EαV =
3nkT
τ E
V
985.0
276.5−
⎟⎠
⎞⎜⎝
⎛=aRκ 2 < R/a < 4
( )2/ aIFn PG π=
AUXAUX
F
P
P
P
PQ α5
==1
2
3
4
5
6
0-D Tokamak Relations
Stand-Alone Fusion Reactor
Q = 40, R/a = 2.6, Bmax = 15 T, PF/AS = 5 MW/m2.
Fission-Fusion Hybrid Reactor
Q = 6.3, R/a = 3.1, Bmax = 15 T, PF/AS = 3 MW/m2.
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)
PART IV: Conclusions
What this all means
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
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?
Acknowledgements
Prof. Ron Parker (fusion)
Prof. Ben Forget (fission)
M. Reed, R. Parker, B. Forget. “A Fission-Fusion Hybrid Reactor in L-Mode Tokamak Configuration with Natural Uranium”. PSFC/RR-11-1 (2011).
MIT Plasma Science and Fusion Center (PSFC) report:
Extra Slides
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).
Hybrid Power
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Q fus =Pfus
Paux
€
Q fis =Pfis
(4 /5)Pfus
€
Qhybrid = Q fus
1
5+
4
5Q fis
⎛
⎝ ⎜
⎞
⎠ ⎟
The fission blanket augments the fusion power.
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
T= 10 keV 100keV
Log
(D-T
rat
e co
effic
ient
)