Robert W. Conn Farrokh Najmabadi University of California San Diego Presentation to:

1. Environmental, Safety, and Economics Studies of Magnetic Fusion, Including Power Plant Design Studies Robert W. Conn Farrokh Najmabadi University of California San Diego Presentation to: SEAB Task Force on Fusion Energy April 28, 1999 Princeton Plasma Physics Laboratory Electronic copy: http://aries.ucsd.edu/najmabadi/TALKS/9904-SEAB/ ARIES Web Site: http:/aries.ucsd.edu/ARIES

2. Scientific & Technical Achievements Projections and Design Options R&D Needs and Development Plan Framework:Assessment Based on Attractiveness & Feasibility Goals and Requirements Periodic Input from Energy Industry Evaluation Based on Customer Attributes Attractiveness Characterization of Critical Issues Feasibility No: Redesign Yes Balanced Assessment of Attractiveness & Feasibility

3. 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.

4. Top-Level Requirements for Commercial Fusion Power Plants 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. Above requirements must be achieved consistent with a competitive life-cycle cost of electricity goal. Extra

5. 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.

6. Portfolio of MFE Configurations Externally ControlledSelf 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

7. 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.

8. 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)

9. 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.

10. 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.

11. 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

12. 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

13. 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. Extra

14. Key Performance Parameters of ARIES-RS

15. 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)

16. 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.

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

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

19. Radioactivity Levels in Fusion Power PlantsAre Very Low and Decay Rapidly after Shutdown 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. • Low afterheat results in excellent safety characteristics • Low specific activity leads to low-level waste that decays away in a few hundreds years. After 100 years, only 10,000 Curies of radioactivity remain in the 585 tonne ARIES-RS fusion core.

20. 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.

21. Laser or Plasma Arc Forming • 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 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. Extra

22. 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.