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The Energy Challenge –Fusion Energy
Farrokh NajmabadiProf. of Electrical EngineeringDirector of Center for Energy ResearchUC San Diego
November 21, 2007
Fusion is one of very few non-carbon based energy options
DT fusion has the largest cross section and lowest temperature (~100M oC). But, it is still a high-temperature plasma!Plasma should be surrounded by a Li-containing blanket to generate T. Or, DT fusion turns its waste (neutrons) into fuel!Through careful design, only a small fraction of neutrons are absorbed in structure and induce radioactivity. For liquid coolant/breeders (e.g., Li, LiPb), most of fusion energy is directly deposited in the coolant simplifying energy recoveryPractically no resource limit (1011 TWy D; 104 (108) TWy 6Li)
D + 6Li → 2 4He + 3.5 MeV (Plasma) + 17 MeV (Blanket)
D + T → 4He (3.5 MeV) + n (14 MeV)n + 6Li → 4He (2 MeV) + T (2.7 MeV)
nT
Two Approaches to Fusion Power –1) Inertial Fusion
Inertial Fusion Energy (IFE)Fast implosion of high-density DT capsules by laser or particle beams (~30 fold radial convergence, heating to fusion temperature).A DT burn front is generated, fusing ~1/3 of fuel (to be demonstrated in National Ignition Facility in Lawrence Livermore National Lab).Several ~300 MJ explosions with large gain (fusion power/input power).
Two Approaches to Fusion Power –2) Magnetic Fusion
Rest of the Talk is focused on MFE
Magnetic Fusion Energy (MFE)Strong magnetic pressure (100’s atm) to confine a low density but high pressure (10’s atm) plasma.Particles confined within a “toroidal magnetic bottle” for 10’s km and 100’s of collisions per fusion event.At sufficient plasma pressure and “confinement time”, the 4He power deposited in the plasma sustains fusion condition.
Plasma behavior is dominated by “collective” effects
Pressure balance (equilibrium) does not guaranty stability.Example: Interchange stability
Impossible to design a “toroidal magnetic bottle” with good curvatures everywhere.Fortunately, because of high speed of particles, an “averaged” good curvature is sufficient.
Outside part of torus inside part of torusFluid Interchange Instability
Tokamak is the most successful concept for plasma confinement
R=1.7 m
DIII-D, General AtomicsLargest US tokamak
Many other configurations possible depending on the value and profile of “q” and how it is generated (internally or externally)
T3 Tokamak achieved the first high temperature (10 M oC) plasma
R=1 m
0.06 MAPlasma Current
JET is currently the largest tokamak in the world
R=3 m
4 MAPlasma Current
Fusion Energy Requirements:
Heating the plasma for fusion reactions to occurto 100 Million Celsius (routinely done in present experiments)
Confining the plasma so that alpha particles sustain fusion burn
Energy Replacement time of about 1 sPlasma density of 1021 /m3 (Air Density is 3X1025 /m3 )Progress in confinement is measured by “Fusion Triple Product” = (plasma temperature)X(energy replacement time)X(plasma density)
Extracting the fusion power and breeding tritiumCo-existence of a hot plasma with material interfaceDeveloping power extraction technology that can operate in fusion environment
Progress in plasma confinement has been impressive
500 MW of fusion Power for 300s Construction will be started shortly in France
Fusi
on tr
iple
pro
duct
n (1
021
m-3
) τ(s
) T(k
eV)
ITER Burning plasma experiment
Large amount of fusion power has also been produced
ITER Burning plasma experiment
DT Experiments
DD Experiments
We have made tremendous progress in understanding fusion plasmas
Substantial improvement in plasma performance though optimization of plasma shape, profiles, and feedback.
Achieving plasma stability at high plasma pressure.Achieving improved plasma confinement through suppression of plasma turbulence, the “transport barrier.”Progress toward steady-state operation through minimization of power needed to maintain plasma current through profile control. Controlling the boundary layer between plasma and vessel wall to avoid localized particle and heat loads.
Fusion: Looking into the future
ITER will demonstrate the technical feasibility of fusion energy
Power-plant scale device. Baseline design:
500 MW of fusion power for 300sDoes not include breeding blanket or power recovery systems.
ITER agreement was signed in Nov. 2006 by 7 international partners (US, EU, Japan, Russa, China, Korea, and India)Construction will begin in 2008.
ARIES-AT is an attractive vision for fusion with a reasonable extrapolation in physics & technology
Competitive cost of electricity (5c/kWh);Steady-state operation;Low level waste;Public & worker safety;High availability.
ITER and satellite tokamaks will provide the necessary data for a fusion power plant
DIII-D DIII-D ITERSimultaneous Max Baseline ARIES-AT
Major toroidal radius (m) 1.7 1.7 6.2 5.2Plasma Current (MA) 2.25 3.0 15 13Magnetic field (T) 2 2 5.3 6.0Electron temperature (keV) 7.5* 16* 8.9** 18**Ion Temperature (keV) 18* 27* 8.1** 18**Density (1020 m-3) 1.0* 1.7* 1.0** 2.2**Confinement time (s) 0.4 0.5 3.7 1.7Normalized confinement, H89 4.5 4.5 2 2.7β (plasma/magnetic pressure) 6.7% 13% 2.5% 9.2%Normalized β 3.9 6.0 1.8 5.4Fusion Power (MW) 500 1,755Pulse length 300 S.S.
* Peak value, **Average Value
The ARIES-AT utilizes an efficient superconducting magnet design
On-axis toroidal field: 6 TPeak field at TF coil: 11.4 T
TF Structure: Caps and straps support loads without inter-coil structure;
Superconducting MaterialEither LTC superconductor (Nb3Sn and NbTi) or HTCStructural Plates with grooves for winding only the conductor.
Use of High-Temperature Superconductors Simplifies the Magnet Systems
HTS does offer operational advantages:
Higher temperature operation (even 77K), or dry magnetsWide tapes deposited directly on the structure (less chance of energy dissipating events)Reduced magnet protection concerns
Inconel strip
YBCO Superconductor Strip Packs (20 layers each)
8.5 430 mm
CeO2 + YSZ insulating coating(on slot & between YBCO layers)
Epitaxial YBCOInexpensive manufacture would consist on layering HTS on structural shells with minimal winding!
DT Fusion requires a T breeding blanket
Requirement: Plasma should be surrounded by a blanket containing Li
D + T → He + nn + 6Li → T + He
Through careful design, only a small fraction of neutrons are absorbed in structure and induce radioactivity
Rad-waste depends on the choice of material: Low-activation materialRad-waste generated in DT fusion is similar to advanced fuels (D-3He)For liquid coolant/breeders (e.g., Li, LiPb), most of fusion energy (carried by neutrons) is directly deposited in the coolant simplifying energy recovery
Issue: Large flux of neutrons through the first wall and blanket:Need to develop radiation-resistant, low-activation material: Ferritic steels, Vanadium alloys, SiC composites
Outboard blanket & first wall
ARIES-AT features a high-performance blanket
Simple, low pressure design with SiC structure and LiPb coolant and breeder.
Innovative design leads to high LiPb outlet temperature (~1,100oC) while keeping SiC structure temperature below 1,000oC leading to a high thermal efficiency of ~ 60%.
Simple manufacturing technique.
Very low afterheat.
Class C waste by a wide margin.
Modular sector maintenance enables high availability
Full sectors removed horizontally on railsTransport through maintenance corridors to hot cells Estimated maintenance time < 4 weeks
ARIES-AT elevation view
Advances in fusion science & technology has dramatically improved our vision of fusion power plants
Estimated Cost of Electricity (c/kWh)
02468
101214
Mid 80'sPhysics
Early 90'sPhysics
Late 90's Physics
AdvancedTechnology
Major radius (m)
0
1
2
3
4
5
6
7
8
9
10
Mid 80's Pulsar
Early 90'sARIES-I
Late 90'sARIES-RS
2000 ARIES-AT
After 100 years, only 10,000 Curies of radioactivity remain in the585 tonne ARIES-RS fusion core.
SiC composites lead to a very low activation and afterheat.All components of ARIES-AT qualify for Class-C disposal under NRC and Fetter Limits. 90% of components qualify for Class-A waste.
Ferritic SteelVanadium
Radioactivity levels in fusion power plantsare very low and decay rapidly after shutdown
Level in Coal Ash
Fusion Core Is Segmented to Minimize the Rad-Waste
Only “blanket-1” and divertorsare replaced every 5 years
Blanket 1 (replaceable)Blanket 2 (lifetime)
Shield (lifetime)
Waste volume is not large
0
50
100
150
200
250
300
350
400
Blanket Shield VacuumVessel
Magnets Structure Cryostat
Cum
ulat
ive
Com
pact
ed W
aste
Vol
ume
(m3)
1270 m3 of Waste is generated after 40 full-power year (FPY) of operation.Coolant is reused in other power plants29 m3 every 4 years (component replacement), 993 m3 at end of service
Equivalent to ~ 30 m3 of waste per FPYEffective annual waste can be reduced by increasing plant service life.
0
200
400
600
800
1000
1200
1400
Class A Class C
Cum
ulat
ive
Com
pact
ed W
aste
Vol
ume
(m3)
90% of waste qualifies for Class A disposal
Fusion: Why is taking so long?
There has been no urgency in developing new sources of energy
Proposed fusion development plan in 1976 aimed at fielding a fusion Demo by 2000.Recent DOE Fusion Development Plan (2003) aimed at fielding a fusion Demo by 2030.
The required funding to implement the plans were not approved.Proposals for fielding a burning plasma experiments since mid 1980s.Fusion program was restructured in mid 1990s, focusing on developing fusion sciences (with 1/3 reduction in US funding).
Fielding a fusion Demo is NOT the official goal of DOE at presentLarge interest and R&D investment in Europe and Japan (and China, India, Korea)
Development of fusion has been constrained by funding!
$M
, FY
02
19
80
FED ITER
Demo Demo
Current cumulative funding
~ 1 week of world energy sale
In Summary, …
In a CO2 constrained world uncertainty abounds
No carbon-neutral commercial energy technology is available today.Carbon sequestration is the determining factor for fossil fuel electric generation.A large investment in energy R&D is needed. A shift to a hydrogen economy or carbon-neutral syn-fuels is also needed to allow continued use of liquid fuels for transportation.
Problem cannot be solved by legislation or subsidy. We need technical solutions.
Technical Communities should be involved or considerable public resources would be wasted
The size of energy market ($1T annual sale, TW of power) is huge. Solutions should fit this size market
100 Nuclear plants = 20% of US electricity production$50B annual R&D represents 5% of energy sale
Status of fusion power
Over 15 MW of fusion power is generated (JET, 1997) establishing “scientific feasibility” of fusion power
Although fusion power < input power.ITER will demonstrate “technical feasibility” of fusion power by generating copious amount of fusion power (500MW for 300s) with fusion power > 10 input power.Tremendous progress in understanding plasmas has helped optimize plasma performance considerably. Vision of attractive fusion power plants exists.Transformation of fusion into a power plant requires considerable R&D in material and fusion nuclear technologies (largely ignored or under-funded to date).
This step, however, can be done in parallel with ITER
Thank you!Any Questions?