RECENT RESULTS FROM USA MAGNETIC FUSION POWER PLANTS Farrokh Najmabadi University of California, San Diego, La Jolla, CA, United States of America German Nuclear Society Annual Meeting on Nuclear Technology May 2004, Düsseldorf, You can download a copy of this presentation from ARIES Web Site:

The ARIES Team Has Examined Several Magnetic Fusion Concept as Power Plants in the Past 15 Years 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) Fusion neutron source study (2000) ARIES-AT advanced technology and advanced tokamak (2000) ARIES-IFE assessment of IFE chambers (2003) ARIES-CS Compact Stellarator Study (Current Research)

Analysis of Conceptual Fusion Power Plants Identifies Key R&D Issues and Provides a Vision for Fusion Research Scientific & Technical Achievements Periodic Input from Energy Industry Goals and Requirements 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

Analysis of Conceptual Fusion Power Plants Identifies Key R&D Issues and Provides a Vision for Fusion Research 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 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 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. 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 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.

Analysis of Conceptual Fusion Power Plants Identifies Key R&D Issues and Provides a Vision for Fusion Research 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

Customer Requirements

Public Acceptance:  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; Public Acceptance:  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; Top-Level Requirements for Fusion Power Plants Was Developed in Consultation with US Industry  Economic Competitiveness: Above requirements must be achieved simultaneously and consistent with a competitive life-cycle cost of electricity. Reliable Power Source:  Closed tritium fuel cycle on site;  Ability to operate at partial load conditions (50% of full power);  Ability to maintain power core (avilability > 80%);  Ability to operate reliably with < 0.1 major unscheduled shut-down per year. Reliable Power Source:  Closed tritium fuel cycle on site;  Ability to operate at partial load conditions (50% of full power);  Ability to maintain power core (avilability > 80%);  Ability to operate reliably with < 0.1 major unscheduled shut-down per year.

Top-Level Requirements Translate into Directions for System Optimization Top –Level Requirements for Commercial Fusion Power  Have an economically competitive life-cycle cost of electricity: Low recirculating power; High power density; High thermal conversion efficiency; Less-expensive systems.  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.

Fusion Plasma

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

Important Parameters of a Fusion Plasma  Fusion power density, P f ~  2 B T 4 and    (I/aB) High magnetic field Higher performance plasma (   )  Recirculating power is dominated by the power to drive and maintain plasma current. Maximize self-driven bootstrap current  Confinement is not a major issue for a power plant size plasma. Important Parameters of a Fusion Plasma  Fusion power density, P f ~  2 B T 4 and    (I/aB) High magnetic field Higher performance plasma (   )  Recirculating power is dominated by the power to drive and maintain plasma current. Maximize self-driven bootstrap current  Confinement is not a major issue for a power plant size plasma. Optimization involves trade-off among various parameters  Trade-off between bootstrap current fraction and   Advanced Tokamak Regime  Trade-off between vertical stability and plasma shape  Trade-off between plasma edge condition and plasma facing components capabilities,  …

Approaching COE insensitive of current drive Approaching COE insensitive of power density Evolution of ARIES Designs 1 st Stability, Nb 3 Sn Tech. ARIES-I’ Major radius (m)8.0   ) 2% (2.9) Peak field (T)16 Avg. Wall Load (MW/m 2 )1.5 Current-driver power (MW)237 Recirculating Power Fraction0.29 Thermal efficiency0.46 Cost of Electricity (c/kWh)10 Reverse Shear Option High-Field Option ARIES-I % (3.0) ARIES-RS 5.5 5% (4.8) ARIES-AT % (5.4)

Detailed Physics Modeling Has Been Performed for ARIES-AT High accuracy equilibria; Large ideal MHD database over profiles, shape and aspect ratio; RWM stable with wall/rotation or wall/feedback control; NTM stable with LHCD; Bootstrap current consistency using advanced bootstrap models; External current drive; Vertically stable and controllable with modest power (reactive); Rough kinetic profile consistency with RS /ITB experiments, as well GLF23 transport code; Modest core radiation with radiative SOL/divertor; Accessible fueling; No ripple losses; 0-D consistent startup;

Fusion Technologies

ARIES-AT Fusion Core

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.

Use of High-Temperature Superconductors Simplifies the Magnet Systems Inconel strip YBCO Superconductor Strip Packs (20 layers each) mm CeO 2 + YSZ insulating coating (on slot & between YBCO layers)  HTS does not offer significant superconducting property advantages over low temperature superconductors due to the low field and low overall current density in ARIES-AT  HTS does offer operational advantages:  Higher temperature operation (even 77K), or dry magnets  Wide tapes deposited directly on the structure (less chance of energy dissipating events)  Reduced magnet protection concerns  and potential significant cost advantages Because of ease of fabrication using advanced manufacturing techniques

Advanced Brayton Cycle Parameters Based on Present or Near Term Technology Evolved with Expert Input from General Atomics *  Key improvement is the development of cheap, high-efficiency recuperators. Recuperator Intercooler 1Intercooler 2 Compressor 1 Compressor 2 Compressor 3 Heat Rejection HX W net Turbine Blanket Intermediate HX 5' 1 2 2' ' 9' 10 6 T S Divertor LiPb Blanket Coolant He Divertor Coolant 11

ARIES-ST Features a High-Performance Ferritic Steel Blanket Typically, the coolant outlet temperature is limited to the max. operating temperature of structural material (550 o C for ferritic steels). By using a coolant/breeder (LiPb), cooling the structure by He gas, and SiC insulators, a coolant outlet temperature of 700 o C is achieved for ARIES-ST leading to 45% thermal conversion efficiency. OB Blanket thickness 1.35 m OB Shield thickness 0.42 m Overall TBR 1.1

 Simple, low pressure design with SiC structure and LiPb coolant and breeder. Outboard blanket & first wall ARIES-AT 2 : SiC Composite Blankets  Simple manufacturing technique.  Very low afterheat.  Class C waste by a wide margin.  LiPb-cooled SiC composite divertor is capable of 5 MW/m 2 of heat load.  Innovative design leads to high LiPb outlet temperature (~1,100 o C) while keeping SiC structure temperature below 1,000 o C leading to a high thermal efficiency of ~ 60%.

Innovative Design Results in a LiPb Outlet Temperature of 1,100 o C While Keeping SiC Temperature Below 1,000 o C Two-pass PbLi flow, first pass to cool SiC f /SiC box second pass to superheat PbLi Bottom Top PbLi Outlet Temp. = 1100 °C Max. SiC/PbLi Interf. Temp. = 994 °C Max. SiC/SiC Temp. = 996°C PbLi Inlet Temp. = 764 °C

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;

Attractiveness: Evaluation Based on Customer Requirements

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)Major radius (m) Approaching COE insensitive of power density High Thermal Efficiency High  is used to lower magnetic field

ARIES-AT is Competitive with Other Future Energy Sources EPRI Electric Supply Roadmap (1/99): Business as usual Impact of $100/ton Carbon Tax. AT 1000 (1 GWe) AT 1500 (1.5 GWe) Estimated range of COE (c/kWh) for 2020* * Data from Snowmass Energy Working Group Summary. Estimates from Energy Information Agency Annual Energy Outlook 1999 (No Carbon tax).

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. 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.

Multi-Dimensional Neutronics Analysis was Performed to Calculate TBR, activities, & Heat Generation Profiles  Very low activation and afterheat Lead to excellent safety and environmental characteristics.  All components qualify for Class-C disposal under NRC and Fetter Limits. 90% of components qualify for Class-A waste.  On-line removal of Po and Hg from LiPb coolant greatly improves the safety aspect of the system and is relatively straight forward.

ARIES-AT Also Uses A Full-Sector Maintenance Scheme

Feasibility: Fusion Development Path

The development path to realize fusion as a practical energy source includes:  Demonstration of high performance, steady-state burning plasmas.  Fusion power technologies are a pace setting element of fusion development. Development of fusion power technologies requires: 1)Strong base program including testing of components in non- nuclear environment as well as fission reactors. 2)Material program including an intense neutron source to develop and qualify low-activation material. 3)A Component Test Facility for integration and test of power technologies in fusion environment.  Fusion power technologies are a pace setting element of fusion development. Development of fusion power technologies requires: 1)Strong base program including testing of components in non- nuclear environment as well as fission reactors. 2)Material program including an intense neutron source to develop and qualify low-activation material. 3)A Component Test Facility for integration and test of power technologies in fusion environment.

ITER-Based Development Path Tokamak physics ITER Base Plasma physics ST, stellarator, RFP, other ICCs Major Facilities Base Technologies 14-MeV neutron source Fusion power technologies Plasma support technologies Decision point DEMO Component Test Facility Theory & Simulation ICC ETRDEMO