Environmental, Safety, and Economics Studies 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 and Requirements

Scientific & TechnicalAchievements

Evaluation Based on Customer Attributes

Attractiveness

Characterizationof Critical Issues

Feasibility

Projections andDesign Options

Balanced Assessment ofAttractiveness & Feasibility

No: RedesignR&D Needs and

Development Plan

Yes

Elements of the Case for Fusion Power Were Developed through Interaction with Representatives of 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 a few 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-down per year.

Top-Level Requirements for Commercial Fusion Power Plants

Extra

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

GOAL: Demonstrate that Fusion Power Can Be a 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 and environmental 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: Stellarator

Confinement field generated by mainly external coils

Toroidal field >> Poloidal field

Large aspect ratio

More stable, better confinement

Example: Field-reversed Configuration

Confinement 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 Power Systems Are Developed Based on a Reasonable Extrapolation of Physics & Technology

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

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

The ARIES Team Has Examined Several Magnetic Fusion 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 a reasonable extrapolation in physics &

technology

Competitive cost of electricity;

Steady-state operation; Low level waste; Public & worker safety; High availability.

The ARIES-RS Utilizes An Efficient Superconducting Magnet Design

TF Coil Design

• 4 grades of superconductor using Nb3Sn and NbTi;

• Structural Plates with grooves for winding only the conductor.

TF Structure

• Caps and straps support loads without inter-coil structure;

• TF cross section is flattened from constant-tension shape to ease PF design.

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

Key Features

• No in-vessel maintenance operations

• Strong poloidal ring supporting gravity and EM loads.

• First-wall zone and divertor plates attached to structural ring.

• No rewelding of elements located within radiation zone

• All plumbing connections in the port are outside the vacuum vessel.

Extra

The ARIES-RS Blanket and Shield Are Segmented to Maximize Component Lifetime

Outer blanket detail

• Blanket and shield consists of 4 radial segments.

• First wall segment, attached to the structural ring, is replaced every 2.5 FPY.

• Blanket/reflector segment is replaced after 7.5 FPY.

• Both shield segments are lifetime components: High-grade heat is

extracted from the high-temperature shield;

Ferritic steel is used selectively as structure and shield filler material. Extra

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

The divertor structures fulfill several essential functions:

1) Mechanical attachment of the plates;

2) Shielding of the magnets;

3) Coolant routing paths for the plates and inboard blanket;

4) “superheating” of the coolant;

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

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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 Has Improved Dramatically in the Last Decade, and Is Directly Tied 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 Key Directions for Spherical Torus Research

• Substantial progress is made towards optimization of high-performance ST equilibria, providing guidance for physics research.

Assessment:

• 1000-MWe ST power plants are comparable in size and cost to advanced tokamak power plants.

• Spherical Torus geometry offers unique design features such as single-piece maintenance.

• Modest size machines can produce significant fusion power, leading to low-cost development pathway for fusion.

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

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

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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 (

Ci/

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 decays away 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 to Reduce 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 nuclear

heating 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-finished

products directly from raw material (powder or bars). Results:

low-cost, accurate, and reliable components.

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

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

• The laser head is directed to lay down the material in accordance with 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 a variety of titanium parts as seen in attached photo. Some are in as-built condition and others machined to final shape. Also see Penn State for additional information.

Laser or Plasma Arc Forming

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Conclusions

• Marketplace and customer requirements establish design requirements and attractive features for a competitive commercial fusion power product.

• Progress in the last decade is impressive and indicates that fusion can achieve its potential as a safe, clean, and economically attractive 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 to R&D directions of the program.

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