ARIES-AT: Evolution of Vision for Advanced Tokamak Power Plants Farrokh Najmabadi University of California, San Diego, La Jolla, CA, United States of America.

ARIES-AT: Evolution of Vision for Advanced Tokamak Power Plants

Farrokh NajmabadiUniversity of California, San Diego, La Jolla, CA, United States of America

Japan-US Workshop on Fusion Power Plants and Related Advanced Technologies with participation of EU March 29-31, 2001 The University of Tokyo, JAPAN

You can download a copy of the presentation from the ARIES Web Site:ARIES Web Site: http://aries.ucsd.edu/

The ARIES Team: Michael C. Billone2, Leslie Bromberg6, Tom H. Brown7, Vincent Chan4, Laila A. El-guebaly8, Phil Heitzenroeder7, Stephen C. Jardin7, Charles Kessel Jr. 7, Lang L. Lao4, Siegfried Malang10, Tak-kuen Mau1, Elsayed A. Mogahed9, Farrokh Najmabadi1, Tom Petrie4, Dave Petti5, Ronald Miller1, Rene Raffray1, Don Steiner8, Igor Sviatoslavsky9, Dai-kai Sze2, Mark Tillack1, Allan D. Turnbull4, Lester Waganer3, Xueren Wang1

1) University of California, San Diego, 2) Argonne National Laboratory, 3) Boeing High Energy Systems, 4) General Atomics, 5) Idaho National Engineering &

Environmental Lab.,6) Massachusetts Institute of Technology, 7) Princeton Plasma Physics Laboratory, 8) Rensselaer Polytechnic Institute, 9) University of Wisconsin - Madison,10) Forschungszentrum Karlsruhe

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;

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;

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

Top-Level Requirements for Commercial Fusion Power Plants

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

Translation of Requirements to GOALS for Fusion Power Plants

Requirements:

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.

Acceptable cost of development.

Improvements “saturate”after a certain limit

Detailed Systems analysis from TITAN reversed-field pinch (1988 $)

There Is Little Economic Benefit for Operating Beyond ~ 5 MW/m2 of Wall Load

Simple analysis for a cylindrical plasma with length L:

r

What we pay for, VFPC

Hyperbolic dependence

Wall loading Iw 1/r

is set by neutron mfp

VFPC = L ( 2r2)

For r >> , VFPC 2 Lr1 / Iw

For r << , VFPC 2 L 2 const.

“Knee of the curve” is at r

High and cheap copper TF Helicity Injection (ohmic current

drive) Freedom of choice of aspect ratio Optimization driven by geometrical

constraints.

There Is Little Economic Benefit for Operating Beyond 5-10 MW/m2 of Wall Load

• ARIES-RS, ARIES-ST, and ARIES-AT have not optimized at the highest wall load (all operate at around 5 MW/m2 peak)

6

7

8

9

10

0 1 2 3 4 5

Avg. wall load (MW/m2)

CO

E (

c/kW

h)

ARIES-RS

Systems code

Hyperbolic dependence4

5

6

7

8

0 1 2 3 4 5

Avg. Wall Load (MW/m2)

CO

E (c

/kW

h)

ARIES-AT

Systems code

Hyperbolic dependence

• Physics & Engineering constraints cause departure from geometrical dependence e.g., high field needed for high load increases TF cost

• ARIES-AT optimizes at lower wall loading because of high efficiency.

ARIES-AT2 Was Launched to Assess the latest Developments in Advanced Tokamak Physics, Technology and Design Concepts

Advanced Tokamak High-performance reversed-shear

plasma Build upon ARIES-RS research; Include latest physics from the

R&D program; Include optimization techniques

devised in the ARIES-ST study; Perform detailed physics analysis

to enhance credibility.

Advanced Technology High-performance, very-low

activation blanket: High thermal conversion

efficiency; Smallest nuclear boundary.

High-temperature superconductors: High-field capability; Ease of operation.

Advanced Manufacturing Techniques Detailed analysis in support of:

Manufacturing; Maintainability; Reliability & availability.

The ARIES-RS Study Set the Goals and Direction of Research for ARIES-AT

Efficiency 610oC outlet (including divertor) Low recirculating power

> 1000 oC coolant outlet > 90% bootstrap fraction

ARIES-RS Performance ARIES-AT Goals Economics

Power Density Reversed-shear Plasma Radiative divertor Li-V blanket with insulating coatings

Higher performance RS Plasma, SiC composite blanket High Tc superconductors

Availability Full-sector maintenance Simple, low-pressure design

Same or better

Safety and Environmental attractiveness

Low afterheat V-alloy No Be, no water, Inert atmosphere Radial segmentation of fusion core to minimize waste quantity

SiC Composites Further attempts to minimize waste quantity

Manufacturing Advanced manufacturing techniques

Major Parameters of ARIES-RS and ARIES-AT

Cost of electricity (c/kWh) 7.5 4.7

ARIES-RS ARIES-ATAspect ratio 4.0 4.0Major toroidal radius (m) 5.5 5.2Plasma minor radius (m) 1.4 1.3Toroidal 5%* 9.2%*

Normalized 4.8* 5.4*

• Designs operate at 90% of maximum theoretical limit.

Plasma elongation (x) 1.9 2.2

Plasma current 11 13Peak field at TF coil (T) 16 11.1Peak/Avg. neutron wall load (MW/m2) 5.4/4 4.9/3.3Thermal efficiency 0.46 0.59Fusion power (MW) 2,170 1,760

Current-drive power to plasma (MW) 81 37Recirculating power fraction 0.17 0.145

Physics Analysis

Continuity of ARIES research has led to the progressive refinement of research

ARIES-I:

• Trade-off of with bootstrap

• High-field magnets to compensate for low

ARIES-II/IV (2nd Stability):

• High only with too much bootstrap

• Marginal reduction in current-drive power

ARIES-RS:

• Improvement in and current-drive power

• Approaching COE insensitive of power density

ARIES-AT:

• Approaching COE insensitive of current-drive

• High is used to reduce toroidal field

Need high equilibria with high bootstrap

Need high equilibria with aligned bootstrap

Better bootstrap alignment

More detailed physics

Impr

oved

Phy

sics

ARIES-AT2: Physics Highlights

Using > 99% flux surface from free-boundary plasma equilibria rather than 95% flux surface used in ARIES-RS leads to larger elongation and triangularity and higher stable

ARIES-AT blanket allows vertical stabilizing shell closer to the plasma, leading to higher elongation and higher

A kink stability shell ( = 10 ms), 1cm of tungsten behind the blanket, is utilized to keep the power requirements for n = 1 resistive wall mode feedback coil at a modest level.

We eliminated HHFW current drive and used only lower hybrid for off-axis current drive.

As a whole, we performed detailed, self-consistent analysis of plasma MHD, current drive, transport, fueling, and divertor.

The ARIES-AT Equilibrium is the Results of Extensive ideal MHD Stability Analysis – Elongation Scans Show an Optimum Elongation

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

ARIES-I Introduced SiC Composites as A High-Performance Structural Material for Fusion

Excellent safety & environmental characteristics (very low activation and very low afterheat).

High performance due to high strength at high temperatures (>1000

oC).

Large world-wide program in SiC: New SiC composite fibers with proper

stoichiometry and small O content. New manufacturing techniques based

on polymer infiltration or CVI result in much improved performance and cheaper components.

Recent results show composite thermal conductivity (under irradiation) close to 15 W/mK which was used for ARIES-I.

Continuity of ARIES research has led to the progressive refinement of research

ARIES-I:

• SiC composite with solid breeders

• Advanced Rankine cycle

Starlite & ARIES-RS:

• Li-cooled vanadium

• Insulating coating

ARIES-ST:

• Dual-cooled ferritic steel with SiC inserts

• Advanced Brayton Cycle at 650 oC

ARIES-AT:

• LiPb-cooled SiC composite

• Advanced Brayton cycle with = 59%

Many issues with solid breeders; Rankine cycle efficiency saturated at high temperature

Max. coolant temperature limited by maximum structure temperature

High efficiency with Brayton cycle at high temperature

Impr

oved

Bla

nket

Tec

hnol

ogy

Outboard blanket & first wall

ARIES-AT2: SiC Composite Blankets

Simple, low pressure design with SiC structure and LiPb coolant and breeder.

Innovative design leads to high LiPb outlet temperature (~1,100oC) while keeping SiC structure temperature below 1,000oC leading to a high thermal efficiency of ~ 60%.

Simple manufacturing technique. Very low afterheat.

Class C waste by a wide margin.

LiPb-cooled SiC composite divertor is capable of 5 MW/m2 of heat load.

Innovative Design Results in a LiPb Outlet Temperature of 1,100oC While Keeping SiC Temperature Below 1,000oC

• Two-pass PbLi flow, first pass to cool SiCf/SiC box second pass to superheat PbLi

q''plasma

Pb-17Li

q'''LiPb

Out

q''back

vback

vFW

Poloidal

Radial

Inner Channel

First Wall Channel

SiC/SiCFirst Wall SiC/SiC Inner Wall

700

800

900

1000

1100

1200800

900

1000

1100

1200

1

2

3

4

5

6

00.020.040.060.080.1

00.020.040.060.080.1

Radial distance (m)

Poloidaldistance(m)

SiC/SiC

Pb-17Li

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

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.

RecuperatorIntercooler 1Intercooler 2

Compressor 1

Compressor 2Compressor 3

HeatRejection

HX

Wnet

Turbine

Blanket

IntermediateHX

5'

1

22'

38

9

4

7'9'

10

6

T

S

1

2

3

4

5 6 7 8

9 10

Divertor

LiPbBlanketCoolant

He DivertorCoolant

11

11

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.

Use of High-Temperature Superconductors Simplifies the Magnet Systems

Inconel strip

YBCO Superconductor Strip Packs (20 layers each)

8.5 430 mm

CeO2 + 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

ARIES-AT Also Uses A Full-Sector Maintenance Scheme

Impact of Advanced Technologies on Fusion Power Plant Characteristics

Impact

Dramatic impact on cost and attractiveness of power plant: Reduces fusion plasma size; Reduces unit cost and enhanced

public acceptance.

Detailed analysis in support of: Manufacturing; Maintainability; Reliability & availability.

Simpler magnet systems Not utilized; Simple conductor, coil, & cryo-

plant. Utilized for High Tc superconductors. High availability of 80-90%

Sector maintenance leads to short schedule down time;

Low-pressure design as well as engineering margins enhance reliability.

Technologies

High-performance, very-low activation blanket: High thermal conversion

efficiency; Smallest nuclear boundary.

High-temperature superconductors: High-field capability; Ease of operation.

Advanced Manufacturing Techniques

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)

0

2

4

6

8

10

12

14

Mid 80'sPhysics

Early 90'sPhysics

Late 90's Physics

AdvancedTechnology

Major radius (m)

0

1

2

3

4

5

6

7

8

9

10

Mid 80's Pulsar

Early 90'sARIES-I

Late 90'sARIES-RS

2000 ARIES-AT

ARIES-AT parameters:Major radius: 5.2 m Fusion Power 1,760 MWToroidal : 9.2% Net Electric 1,000 MWAvg. Wall Loading: 3.3 MW/m2 COE 4.7

c/kWh

Summary

• Identification of top-level requirements are essential in developing conceptual designs of fusion power plants.

• ARIES designs have explored the wide range of advanced tokamak power plants:

* ARIES-I: First Stability * ARIES-RS: Nominal reversed shear

* ARIES-II: Second Stability * ARIES-AT: Aggressive reversed shear

• Combination of advanced tokamak physics and advanced technologies lead to attractive fusion systems.

• Achieving full safety and environmental potential of fusion is an absolute necessity (but it is not sufficient).

• The goal of the US program in power plant studies is to guide fusion R&D. It strives for a balance between attractiveness (extrapolation in data base) and creditability. Past history indicates that we have been typically projecting only 10 years ahead!