Environmental, Safety, and EconomicsStudies of Magnetic Fusion,Including Power Plant Design Studies

Robert W. ConnFarrokh NajmabadiUniversity of California San Diego

Presentation to:SEAB Task Force on Fusion EnergyApril 28, 1999Princeton Plasma Physics Laboratory

Electronic copy: http://aries.ucsd.edu/najmabadi/TALKS/9904-SEAB/

ARIES Web Site: http:/aries.ucsd.edu/ARIES

Framework:Assessment Based on Attractiveness & Feasibility

Periodic Input fromEnergy Industry

Goals andRequirements

Scientific & TechnicalAchievements

Evaluation Based on Customer Attributes

Attractiveness

Characterizationof Critical Issues

Feasibility

Projections andDesign Options

Balanced Assessment ofAttractiveness & Feasibility

No: Redesign R&D Needs andDevelopment Plan

Yes

Elements of the Case for Fusion Power WereDeveloped through Interaction with Representativesof U.S. Electric Utilities and Energy Industry

• Clear life-cycle cost advantage over other power station options;

• Ease of licensing;

• No need for evacuation plan;

• No high-level waste;

• Reliable, available, and stable as an electrical power source;

• No local or global atmospheric impact;

• Closed, on-site fuel cycle;

• High fuel availability;

• Capable of partial load operation;

• Available in a range of unit sizes.

• No public evacuation plan is required: total dose < 1 rem at site boundary;

• Generated waste can be returned to environment or recycled in less than afew hundred years (not geological time-scale);

• No disturbance of public’s day-to-day activities;

• No exposure of workers to a higher risk than other power plants;

• Closed tritium fuel cycle on site;

• Ability to operate at partial load conditions (50% of full power);

• Ability to maintain power core;

• Ability to operate reliably with less than 0.1 major unscheduled shut-downper year.

Top-Level Requirements forCommercial Fusion Power Plants

Extra

• Above requirements must be achieved consistent with acompetitive life-cycle cost of electricity goal.

GOAL: Demonstrate that Fusion Power Can Bea Safe, Clean, & Economically Attractive Option

Requirements:

• Have an economically competitive life-cycle cost of electricity:∗ Low recirculating power;

∗ High power density;

∗ High thermal conversion efficiency.

• Gain Public acceptance by having excellent safety andenvironmental characteristics:

∗ Use low-activation and low toxicity materials and care in design.

• Have operational reliability and high availability:∗ Ease of maintenance, design margins, and extensive R&D.

• Acceptable cost of development.

Portfolio of MFE Configurations

Externally Controlled Self Organized

Example: StellaratorConfinement field generated by

mainly external coils

Toroidal field >> Poloidal field

Large aspect ratio

More stable, better confinement

Example: Field-reversed ConfigurationConfinement field generated mainly by

currents in the plasma

Poloidal field >> Toroidal field

Small aspect ratio

Simpler geometry, higher power density

Conceptual Design of Magnetic Fusion PowerSystems Are Developed Based on a ReasonableExtrapolation of Physics & Technology

• Plasma regimes of operation are optimized based on latestexperimental achievements and theoretical predictions.

• Engineering system design is based on “evolution” of present-day technologies, i.e., they should be available at least in smallsamples now. Only learning-curve cost credits are assumed incosting the system components.

The ARIES Team Has Examined Several MagneticFusion Concept as Power Plants in the Past 10 Years

• TITAN reversed-field pinch (1988)

• ARIES-I first-stability tokamak (1990)

• ARIES-III D-3He-fueled tokamak (1991)

• ARIES-II and -IV second-stability tokamaks (1992)

• Pulsar pulsed-plasma tokamak (1993)

• SPPS stellarator (1994)

• Starlite study (1995) (goals & technical requirements for power plants & Demo)

• ARIES-RS reversed-shear tokamak (1996)

• ARIES-ST spherical torus (1999)

ARIES-RS is an attractive vision for fusion with areasonable extrapolation in physics & technology

∗ Competitive cost ofelectricity;

∗ Steady-state operation;

∗ Low level waste;

∗ Public & worker safety;

∗ High availability.

The ARIES-RS Utilizes An EfficientSuperconducting Magnet Design

TF Coil Design

• 4 grades of superconductorusing Nb3Sn and NbTi;

• Structural Plates withgrooves for winding onlythe conductor.

TF Structure

• Caps and straps supportloads without inter-coilstructure;

• TF cross section is flattenedfrom constant-tension shapeto ease PF design.

The ARIES-RS Replacement Sectors areIntegrated as a Single Unit for High Availability

Key Features

• No in-vessel maintenanceoperations

• Strong poloidal ringsupporting gravity andEM loads.

• First-wall zone anddivertor plates attached tostructural ring.

• No rewelding of elementslocated within radiationzone

• All plumbing connectionsin the port are outside thevacuum vessel.

Extra

The ARIES-RS Blanket and Shield AreSegmented to Maximize Component Lifetime

Outer blanket detail• Blanket and shield consists of

4 radial segments.

• First wall segment, attachedto the structural ring, isreplaced every 2.5 FPY.

• Blanket/reflector segment isreplaced after 7.5 FPY.

• Both shield segments arelifetime components:

∗ High-grade heat isextracted from the high-temperature shield;

∗ Ferritic steel is usedselectively as structureand shield filler material. Extra

The divertor is part of the replacement module,and consists of 3 plates, coolant and vacuummanifolds, and the strongback support structure

The divertor structures fulfillseveral essential functions:1) Mechanical attachment ofthe plates;

2) Shielding of the magnets;

3) Coolant routing paths for theplates and inboard blanket;

4) “superheating” of thecoolant;

5) Contribution to the breedingratio, since Li coolant is used.

Extra

Key Performance Parameters of ARIES-RS

Requirements Design Feature Performance Level

Economics COE 7.5 c/kWh

Power Density Reversed-shear PlasmaLi-V blanket with insulating coatingRadiative divertor

Wall load:5.6/4.0 MW/m2

Surface heat flux:6.0/2.0 MW/m2

Efficiency 610o C outlet (including divertor)Low recirculating power

46% gross efficiency~90% bootstrap fraction

Lifetime Radiation-resistant V-alloy 200 dpa

Availability Full-sector maintenanceSimple, low-pressure design

1 month< 1 MPa

Safety Low afterheat V-alloyNo Be, no water, Inert atmosphere

< 1 rem worst-case off-sitedose (no evacuation plan)

Environmentalattractiveness

Low activation materialRadial segmentation of fusion core

Low-level waste (Class-A)Minimum waste volume

Our Vision of Magnetic Fusion Power Systems HasImproved Dramatically in the Last Decade, and Is DirectlyTied to Advances in Fusion Science & Technology

Estimated Cost of Electricity (c/kWh) Volume of Fusion Core (m3)

02468

101214

Mid 80'sPhysics

Early 90'sPhysics

Late 90's Physics

1 Gwe 2 Gwe

0

1000

2000

3000

4000

Mid 80's Pulsar

Early 90'sARIES-I

Late 90'sARIES-RS

1 Gwe 2 Gwe

The ARIES-ST Study Has Identified KeyDirections for Spherical Torus Research

• Substantial progress is madetowards optimization of high-performance ST equilibria,providing guidance for physicsresearch.

Assessment:

• 1000-MWe ST power plants arecomparable in size and cost toadvanced tokamak power plants.

• Spherical Torus geometry offersunique design features such assingle-piece maintenance.

• Modest size machines canproduce significant fusion power,leading to low-cost developmentpathway for fusion.

Spherical Torus Geometry Offers Some UniqueDesign Features (e.g., Single-Piece Maintenance)

Spherical Torus Geometry Offers Some UniqueDesign Features (e.g., Single-Piece Maintenance)

Extra

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

104 105 106 107 108 109 1010 1011

ARIES-STARIES-RS

Act

ivit

y (C

i/W

th)

Time Following Shutdown (s)

1 mo 1 y 100 y1 d

Radioactivity Levels in Fusion Power PlantsAre Very Low and Decay Rapidly after Shutdown

• Low afterheat results in excellent safety characteristics

• Low specific activity leads to low-level waste that decaysaway in a few hundreds years.

ARIES-RS: V Structure, Li Coolant;

ARIES-ST: Ferritic Steel Structure,

He coolant, LiPb Breeder;

Designs with SiC composites will

have even lower activation levels.

After 100 years, only 10,000 Curies

of radioactivity remain in the

585 tonne ARIES-RS fusion core.

Advances in Physics and Technology Are Helping toReduce the Cost of Fusion Systems Substantially.Continued Improvements Can Reasonably Be Expected.Examples:• Higher performance plasmas (e.g, Advanced tokamak, ST);

• High-Temperature Superconductors:∗ Operation at higher fields;

∗ Operation at higher temperatures and decreased sensitivity to nuclearheating simplifies cryogenics.

• Advanced Manufacturing Techniques:∗ Manufacturing cost can be more than 20 times the raw material costs;

∗ New “Rapid Prototyping” techniques aim at producing near-finishedproducts directly from raw material (powder or bars). Results:

low-cost, accurate, and reliable components.

⇒ Visions for Fusion Power Systems Provide Essential Guidance toFusion Science & Technology R&D.

• A laser or plasma-arc deposits alayer of metal (from powder) on ablank to begin the material buildup

• The laser head is directed to laydown the material in accordancewith a CAD part specification

Beam and PowderInteraction Region

Z-Axis Positioningof Focusing Lensand Nozzle

High PowerLaser

PowderDeliveryNozzle

PositioningTable

Preform

Formed Part

Schematic of Laser Forming Process

AeroMet has produced avariety of titanium partsas seen in attached photo.Some are in as-builtcondition and othersmachined to final shape.Also see Penn State foradditional information.

Laser or Plasma Arc Forming

Extra

Conclusions

• Marketplace and customer requirements establish designrequirements and attractive features for a competitive commercialfusion power product.

• Progress in the last decade is impressive and indicates that fusioncan achieve its potential as a safe, clean, and economicallyattractive power source.

• Key requirements for fusion research:

∗ A reduced cost development path

∗ Lower capital investment in plants.

• Visions for fusion power systems provide essential guidance toR&D directions of the program.

• Progress in plasma physics understanding and engineering andtechnology are the key elements in achieving the goals of fusion.