Recent Advances in Fusion:The Energy Source for the XXI Century

Mohamed AbdouDistinguished Professor, Mechanical and Aerospace Engineering Department

Director, Center for Energy Science and Technology Advanced Research (CESTAR)Director, Fusion Science and Technology Center

University of California Los Angeles (UCLA)

The Second International Conference on Thermal Engineering Theory and Applications   

January 3-6, 2006 Al Ain, United Arab Emirates

What is Nuclear Fusion?

• Nuclear Fusion is the energy-producing process taking place in the core of the Sun and stars

• The core temperature of the Sun is about 15 million °C. At these temperatures hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth via sunlight

Fusion Reactions• Deuterium – from water

(0.02% of all hydrogen is heavy hydrogen or deuterium)

• Tritium – from lithium(a light metal common in the Earth’s crust)

Deuterium + Lithium → Helium + Energy

This fusion cycle (which has the fastest reaction rate) is of interest for Energy Production

The World, particularly in developing countries, needs a New Energy Source

• Growth in world population and growth in energy demand from increased industrialisation/affluence will lead to an Energy Gap which will be increasingly difficult to fill with fossil fuels

• Without improvements in efficiency we will need 80% more energy by 2020• Even with efficiency improvements at the limit of technology we would still

need 40% more energy

World Energy Scene* (I)World Energy Scene* (I)1) The world uses a lot of energy

Average power consumption = 13.6 TWs, or 2.2 kWs per person

World energy market ~ $3 trillion/yr (electricity ~$1 trillion/yr)

- very unevenly (OECD 6.2 kW/person; Bangladesh 0.20 kW/person; China 1.3kW/person)

2) World energy use is expected to grow

- growth necessary to lift billions of people out of poverty

3) 80% is generated by burning fossil fuels

climate change & debilitating pollution

- which won’t last for ever

*See Sir Chris Llewellyn-Smith, FPA, October 11, 2005

Need major new (clean) energy sources

- requires new technology

Future Energy UseFuture Energy Use

The International Energy Agency (IEA) expects the world’s energy use to increase 60% by 2030 (while population expected to grow from 6.2B to 8.1B) - driven largely by growth of energy use and population in India (current use = 0.7 kWs/person, vs. OECD average of 6.2 kWs/person) and China (current use = 1.3 kWs/person)

Strong link between energy use and the Human Development Index (HDI ~ life expectancy at birth + adult literacy and school enrolment + gross national product per capita at purchasing power parity) – need increased energy use to lift billions out of poverty

Carbon dioxide levels over the last 60,000 years - we are provoking the atmosphere!

Source University of Berne and National Oceanic, and Atmospheric Administration

Meeting the Energy Challenge Requires:Meeting the Energy Challenge Requires:Fiscal measures to change the behaviour of consumers,

and provide incentives to expand use of low carbon technologies

Actions to improve efficiency (domestic, transport, …)

Use of renewables where appropriate (although locally useful, not hugely significant globally)

BUT only four sources capable in principle of meeting a large fraction of the world’s energy needs:

• Burning fossil fuels (currently 80%) - develop & deploy CO2 capture and storage

• Solar - seek breakthroughs in production and storage• Nuclear fission - hard to avoid if we are serious about reducing fossil

fuel burning (at least until fusion available)• Fusion - with so few options, we must develop fusion as fast as

possible, even if success is not 100% certain

ITER

• The World is about to construct the next step in fusion development, a device called ITER

• ITER will demonstrate the scientific and technological feasibility of fusion energy for peaceful purposes

• ITER will produce 500 MW of fusion power

• Cost, including R&D, is 15 billion dollars

ITER Design - Main Features

Divertor

Central Solenoid

Outer Intercoil Structure

Toroidal Field Coil

Poloidal Field Coil

Machine Gravity Supports

Blanket Module

Vacuum Vessel

Cryostat

Port Plug (IC Heating)

Torus Cryopump

ITER is a collaborative effort among Europe, Japan, US, Russia, China, South Korea, and India

ITER Location

Caradache (France) Rokkasho (Japan)

Cadarache was selected as the ITER construction site. There will be some facilities in Rokassho under the “Broader Approach” agreement.

Fusion Power Station Schematic

Fusion Nuclear Technology (FNT)

FNT Components from the edge of the Plasma to TF Coils (Reactor “Core”)

1. Blanket Components

2. Plasma Interactive and High Heat Flux Components

3. Vacuum Vessel & Shield Components

4. Tritium Processing Systems

5. Instrumentation and Control Systems

6. Remote Maintenance Components

7. Heat Transport and Power Conversion Systems

a. Divertor, limiter

b. RF antennas, launchers, wave guides, etc.

Other Components affected by the Nuclear Environment

Fusion Power & Fuel Cycle Technology

Plasma

Radiation

Neutrons

Coolant for energy conversion

First Wall

Shield

Blanket Vacuum vessel

Magnets

Tritium breeding zone

Blanket (including first wall)Blanket Functions:

A. Power Extraction– Convert kinetic energy of neutrons and secondary gamma rays into heat

– Absorb plasma radiation on the first wall

– Extract the heat (at high temperature, for energy conversion)

B. Tritium Breeding– Tritium breeding, extraction, and control

– Must have lithium in some form for tritium breeding

C. Physical Boundary for the Plasma– Physical boundary surrounding the plasma, inside the vacuum vessel

– Provide access for plasma heating, fueling

– Must be compatible with plasma operation

– Innovative blanket concepts can improve plasma stability and confinement

D. Radiation Shielding of the Vacuum Vessel

Blanket Materials1. Tritium Breeding Material (Lithium in some form)

Liquid: Li, LiPb (83Pb 17Li), lithium-containing molten salts

Solid: Li2O, Li4SiO4, Li2TiO3, Li2ZrO3

2. Neutron Multiplier (for most blanket concepts)

Beryllium (Be, Be12Ti)

Lead (in LiPb)

3. Coolant

– Li, LiPb – Molten Salt – Helium – Water

4. Structural Material– Ferritic Steel (accepted worldwide as the reference for DEMO)

– Long-term: Vanadium alloy (compatible only with Li), and SiC/SiC

5. MHD insulators (for concepts with self-cooled liquid metals)

6. Thermal insulators (only in some concepts with dual coolants)

7. Tritium Permeation Barriers (in some concepts)

8. Neutron Attenuators and Reflectors

A Helium-Cooled Li-Ceramic Breeder Concept: Example

Material Functions•Beryllium (pebble bed) for neutron multiplication

•Ceramic breeder (Li4SiO4, Li2TiO3, Li2O, etc.) for tritium breeding

•Helium purge (low pressure) to remove tritium through the “interconnected porosity” in ceramic breeder

•High pressure Helium cooling in structure (ferritic steel)Several configurations exist (e.g. wall parallel or “head on” breeder/Be arrangements)

Li/Vanadium Blanket Concept

Breeding Zone

(Li flow)

Primary Shield

Secondary Shield

Reflector

Li

Li

Li

Secondary shield(B4C)

Primary shield

(Tenelon)

Reflector

Lithium

Lithium

Vanadium structure

Vanadium structure

Pathway Toward Higher Temperature Through Innovative Designs with Current Structural Material (Ferritic Steel):

Dual Coolant Lead-Lithium (DCLL) FW/Blanket Concept

First wall and ferritic steel structure cooled with helium

Breeding zone is self-cooled Structure and Breeding zone are

separated by SiCf/SiC composite flow channel inserts (FCIs) that Provide thermal insulation to

decouple PbLi bulk flow temperature from ferritic steel wall

Provide electrical insulation to reduce MHD pressure drop in the flowing breeding zone

Self-cooled Pb-17Li

Breeding Zone

He-cooled steel

structure

SiC FCI

DCLL Typical Unit Cell

Pb-17Li exit temperature can be significantly higher than the operating temperature of the steel structure High Efficiency

Flows of electrically conducting coolants will experience complicated magnetohydrodynamic (MHD) effects

What is magnetohydrodynamics (MHD)?– Motion of a conductor in a magnetic field produces an EMF that can

induce current in the liquid. This must be added to Ohm’s law:

– Any induced current in the liquid results in an additional body force in the liquid that usually opposes the motion. This body force must be included in the Navier-Stokes equation of motion:

– For liquid metal coolant, this body force can have dramatic impact on the flow: e.g. enormous MHD drag, highly distorted velocity profiles, non-uniform flow distribution, modified or suppressed turbulent fluctuations

)( BVEj

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Large MHD drag results in large MHD pressure drop

• Net JxB body force p = cVB2 where c = (tw w)/(a )

• For high magnetic field and high speed (self-cooled LM concepts in inboard region) the pressure drop is large

• The resulting stresses on the wall exceed the allowable stress for candidate structural materials

• Perfect insulators make the net MHD body force zero

• But insulator coating crack tolerance is very low (~10-7).

– It appears impossible to develop practical insulators under fusion environment conditions with large temperature, stress, and radiation gradients

• Self-healing coatings have been proposed but none has yet been found (research is on-going)

Lines of current enter the low resistance wall – leads to very high induced current and high pressure drop

All current must close in the liquid near the wall – net drag

from jxB force is zero

Conducting walls Insulated wall

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Many liquid wall reactor concepts for high power density were conceived & analyzed in APEX

Thin liquid wall concept (blanket region behind LW not shown)

Many candidate liquids were studied: Li, Sn-Li, Sn, Flibe and Flinabe

Several liquid wall flow schemes were conceived: – Thick liquid walls– Thin fast flowing protection layer (CLIFF)– Inertial or EM assisted wall adhesion– Integrated or stand-alone divertors

Concept performance was analyzed from many perspectives– Liquid wall flow MHD and heat transfer– Breeding, shielding and activation potential– Simplicity of system design, maintenance

Interactions of liquid walls with plasma operation were emphasized– Plasma edge effects, impurities & recycling– Liquid metal motion coupling to plasma modes

SurfaceRenewal

DivertorCassette

Fast FlowCassette

OutboardFast Flow

InboardFastFlow

Bottom DrainFlow

HIMAG simulation of the above experiment

Flow Velocity : 3 m/s Average surface normal field gradient: 0.6 T/m

New simulation tools and experimental facilities used to address flowing liquid metals in NSTX divertor fields – now

being applied to DCLL-TBM

New phenomenon observed in both experiments and numerical simulation for film flows in NSTX divertor: the liquid film tends to ‘pinch in’ away from the wall under a positive surface normal magnetic field gradient.

‘Pinching in’

Gallium flow experiment at UCLA M-TOR facility

Simulation with MHD research code (at UCLA) shows tendency for strong reversed flow jets near slot or crack in flow channel insert (MTOR experiments in development)

PbLi

FCI

Summary

• The D-T Fusion process offers the promise of:– Virtually unlimited energy source from cheap abundant fuels;– No atmospheric pollution of greenhouse and acid rain gases;– Low radioactive burden from waste for future generations.

• Tremendous Progress has been achieved over the past decades in plasma physics and fusion technology.

• Fusion R&D involves many challenging areas of physics and technologies and is carried out through extensive international collaboration

• EU, JA, USA, RF, PRC, Korea, and India are about to construct ITER to demonstrate the scientific and technological feasibility of fusion energy (ITER will produce 500MW of fusion power )