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: ARIES Web Site:

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

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- 3 He-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 Nb 3 Sn 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. Extra

Key Performance Parameters of ARIES-RS

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 (m 3 )

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)

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Radioactivity Levels in Fusion Power Plants Are 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 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 Extra

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.