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

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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)

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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

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Blanket Shield VacuumVessel

Magnets Structure Cryostat

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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.

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Class A Class C

Cum

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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?