REALIZATION OF FUSION AS THE ULTIMATE ENERGY SOURCE FOR HUMANITY

Mohamed AbdouDistinguished Professor of Engineering and Applied Science

Director, Center for Energy Science and Technology (CESTAR)Director, Fusion Science and Technology CenterUniversity of California, Los Angeles (UCLA)

web: http://www.fusion.ucla.edu/abdou/

Invited Keynote Lecture in ExHFT-7:7th World Conference on

Experimental Heat Transfer, Fluid Mechanics and Thermodynamics

Krakow, Poland June 28-July 3, 2009

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REALIZATION OF FUSION AS THE ULTIMATE ENGERGY SOURCE FOR HUMANITY

OUTLINE• Fusion Research Transition and DEMO Goal

• ITER

• Blanket Principles and Interactions

• MHD Thermofluid Issues

• Blanket Types and Issues

• Science-based framework for FNST Development

• Blanket Testing in ITER

• Need for a New Fusion Nuclear Facility

• Summary

077-05/rs

3

What is fusion? Fusion powers the Sun and Stars. Two light nuclei combine to form a

heavier nuclei (the opposite of nuclear fission).

Deuterium and tritium is the easiest, attainable at lower plasma temperature, because it has the largest reactionrate and high Q value.

The World Program is focused on the D-T Cycle

Illustration from DOE brochure

E = mc2

17.6 MeV80% of energy 80% of energy release release (14.1 MeV)(14.1 MeV)

Used to breed Used to breed tritium and close tritium and close the DT fuel cyclethe DT fuel cycle

Li + n → T + HeLi + n → T + HeLi in some form must be Li in some form must be used in the fusion used in the fusion system system

20% of energy release 20% of energy release

(3.5 MeV)(3.5 MeV)

DeuteriumNeutron

Tritium Helium

Incentives for Developing FusionIncentives for Developing Fusion

Sustainable energy source

(for DT cycle: provided that Breeding Blankets are successfully developed and tritium self sufficiency conditions are satisfied)

No emission of Greenhouse or other polluting gases

No risk of a severe accident

No long-lived radioactive waste

Fusion energy can be used to produce electricity and hydrogen, and for desalination.

5

Fusion Research is about to transition from Plasma Physics to Fusion Science and Engineering

• 1950-2010– The Physics of Plasmas

• 2010-2035– The Physics of Fusion – Fusion Plasmas-heated and sustained

• Q = (Ef / Einput )~10• ITER (magnetic fusion) and NIF (inertial fusion)

• 2010-2040 ?– Fusion Nuclear Science and Technology for Fusion – DEMO by 2040?

• > 2050 ?– Large scale deployment!

(illustration is from JAEA DEMO Design)

Cryostat Poloidal Ring Coil

Coil Gap Rib Panel

Blanket

VacuumVessel

Center Solenoid Coil Toroidal Coil

Maint.Port

Plasma

The World Fusion Program has a Goal for a Demonstration Power Plant (DEMO) by ~2040(?)

Plans for DEMO are based on Tokamaks

7

ITER• The World has started construction of 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 is a collaborative effort among Europe, Japan, US, Russia, China, South Korea, and India. ITER construction site is Cadarache, France.

• ITER will begin operation in hydrogen in ~2019. First D-T Burning Plasma in ITER in ~ 2026

ITER is a reactor-grade tokamak plasma physics experiment - a huge step toward fusion energy

JET

~15 m

ITER

~29 m

By Comparison, JET

~10 MW ~1 sec Passively

Cooled

Will use D-T and produce neutrons 500MW fusion power, Q=10 Burn times of 400s Reactor scale dimensions Actively cooled PFCs Superconducting magnets

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Magnet System in Tokamak (e.g. ITER) has 4 sets of coils • 18 Toroidal Field (TF) coils

produce the toroidal magnetic field to confine and stabilize the plasma

− Superconducting, Nb3Sn/Cu/SS

− Max. field: 11.8T

• 6 Poloidal Field (PF) coils position and shape the plasma

− Superconducting, NbTi/Cu/SS

− Max. field: 6T

• Central Solenoid (CS) coil induces current in the plasma

− Superconducting, Nb3Sn/Cu/alloy908

−Max. field: 13.5T

TF coil case provides main structure of the magnet system and machine core

• 18 Correction coils correct error fields− Superconducting, NbTi/Cu/SS− Max. field < 6T

Stored energy in ITER magnetic field is large ~ 1200 MJEquivalent to a fully loaded 747 moving at take off speed 265 km/h

New Long-Pulse Confinement and Other Facilities Worldwide will Complement ITER

ITER Operations: 34% Europe 13% Japan 13% U.S. 10% China 10% India 10% Russia 10% S. Korea

China

Europe

India

Japan (w/EU)

South Korea

U.S.

EAST

Being plannedFusion Nuclear Science &Technology Testing Facility (FNSF/CTF/VNS)

KSTARW7-X(also JT-60SA)

JT-60SA(also LHD)

SST-1

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Plasma

Radiation

Neutrons

Coolant for energy extraction

First Wall

Shield

Blanket Vacuum vessel

Magnets

Tritium breeding zone

The primary functions of the blanket are to provide for: Power Extraction & Tritium Breeding

DT

Lithium-containing Liquid metals (Li, PbLi) are strong candidates as breeder/coolant

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Fusion Nuclear Science and Technology (FNST)

FNST includes the scientific issues and technical disciplines as well as materials, engineering and development of fusion nuclear components:

From the edge of Plasma to TF Coils:

1. Blanket Components (includ. FW)

2. Plasma Interactive and High Heat FluxComponents (divertor, limiter, rf/PFC element, etc)

3. Vacuum Vessel & Shield Components

Fusion Power & Fuel Cycle Technology

The location of the Blanket inside the vacuum vessel is necessary but has

major consequences:

a- many failures (e.g. coolant leak) require immediate shutdown

b- repair/replacement take long time

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Fusion environment is unique and complex:multi-component fields with gradients

R

Bp

BT

0

B

InnerEdge

OuterEdge

PlasmaWidth

•Neutron and Gamma fluxes•Particle fluxes

•Heat sources (magnitude and gradient)– Surface (from plasma radiation)– Bulk (from neutrons and gammas)

• Magnetic Field (3-component)– Steady field– Time varying field

• With gradients in magnitude and direction

Multi-function blanket in multi-component field environment leads to:- Multi-Physics, Multi-Scale Phenomena Rich Science to Study

- Synergistic effects that cannot be anticipated from simulations & separate effects tests. Modeling and Experiments are challenging

(for ST)

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Fusion Nuclear Science & Technology Issues

1. Tritium Supply & Tritium Self-Sufficiency

2. High Power Density

3. High Temperature

4. MHD for Liquid Breeders / Coolants

5. Tritium Control (Extraction and Permeation)

6. Reliability / Maintainability / Availability

7. Testing in Fusion Facilities

Challenging

1616

Flows of electrically conducting coolants will experience complicated MHD effects in the magnetic fusion environment 3-component magnetic field and complex geometry

– 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

BjgVVVV

11

)( 2pt

Dominant impact on LM design. Challenging Numerical/Computational/Experimental Issues

MHD Characteristics of Fusion Liquid Breeder Blanket Systems

1818

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

- Net JxB body force

p = VB2 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 walls

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Impact of MHD and no practical Insulators :No self-cooled blanket option

Self-Cooled liquid Metal Blankets are NOT feasible now because of MHD Pressure Drop

A perfectly insulated “WALL” can solve the problem, but is it practical?

1919

Separately-cooled LM Blanket Example: PbLi Breeder/ helium Coolant with RAFM

EU mainline blanket design All energy removed by separate

Helium coolant The idea is to avoid MHD issues.

But, PbLi must still be circulated to extract tritium

ISSUES:– Low velocity of PbLi leads to high

tritium partial pressure , which leads to tritium permeation (Serious Problem)

– Tout limited by PbLi compatibility with RAFM steel structure ~ 470 C (and also by limit on Ferritic, ~550 C)

Possible MHD Issues : – MHD pressure drop in the inlet

manifolds– B- Effect of MHD buoyancy-driven flows

on tritium transport

Drawbacks: Tritium Permeation and limited thermal efficiency

Module box (container & surface heat flux extraction)

Breeder cooling unit (heat extraction from PbLi)

Stiffening structure (resistance to accidental in-box pressurization i.e He leakage) He collector system

(back)

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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

FCI does not serve structural function

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

077-05/rs

2121

High pressure drop is only one of the MHD issues for LM blankets; MHD heat and mass transfer are also of great importance!

and hence disturb current flow and velocity, and redistribute energy

Instabilities and 3D MHD effects in complex detailed geometry and configuration with magnetic and nuclear fields gradients have major impact.

• Unbalanced pressure drops (e.g. from insulator cracks) leading to flow control and channel stagnation issues

• Unique MHD velocity profiles and instabilities affecting transport of mass and energy

Accurate Prediction of MHD Heat &Mass Transfer is essential to addressing important issues such as:

• thermal stresses, • temperature limits,• failure modes for structural and

functional materials, • thermal efficiency, and • tritium permeation.

FCI overlap gaps act as conducting breaks in FCI insulation

Courtesy of Munipalli et al.

(Ha=1000; Re=1000; =5 S/m, cross-sectional dimension expanded 10x)

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Buoyancy effects in DCLL blanket

max( ) ~ exp{ }q r q r

DCLL DEMO blanket, US

Vorticity distribution in the buoyancy-assisted (upward) poloidal flow

Caused by

and associated

Can be 2-3 times stronger than forced flows. Forced flow: 10 cm/s. Buoyant flow: 25-30 cm/s

In buoyancy-assisted (upward) flows, buoyancy effects may play a positive role due to the velocity jet near the “hot” wall, reducing the FCI T

In buoyancy-opposed (downward) flows, the effect may be negative due to recirculation flows

Effect on the interface T, FCI T,

heat losses, tritium transport

)()( max rExpqrq

Kk

aqT 3

2max 10~

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Corrosion Is A Serious Issue For LM Blankets

• At present, the interface temperature between PbLi and Ferritic Steel (FS) is limited to < 470 C because of corrosion

– This is very restrictive and does not allow higher temperature operation with FS or advanced ODS.

• Data available are from corrosion experiments with no magnetic field. They are static or dynamic.

– Results show strong dependence on temperature and on the velocity of PbLi.– Therefore, corrosion should be expected to experience MHD effects due to sharp

changes in the velocity and temperature profiles.– There is experimental evidence of the effect of magnetic field.

• Criteria for determining the allowable interface temperature :a) thinning of the walls (in the “hot” section) due to corrosion b) deposition of the corrosion products transported in the heat transport loop to the Heat

Exchanger (“cold” section) causing radioactive “CRUD” that hampers HX maintenance.c) corrosion products deposition in the “cold” section causing clogging small orifices,

valves, etc.

Usually the criterion c) is applied with the assumption, that the corrosion rate has to be limited to 20 micron/year in order to avoid clogging. This leads to an allowable interface temperature of ~ 470 C as measured in  experiments with turbulent flow without magnetic fields

• Experiments with sodium loops have shown that deposits in the "cold" sections is more limiting than thinning of the "hot" walls

Hence, in addition to corrosion rates, it is important to predict the behavior of the corrosion products in the entire heat transport loop, particularly “deposition”.

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Macrostructure of the washed samples after contact with the PbLi flow

B=0 T

B=1.8 T

From: F. Muktepavela et al. EXPERIMENTAL STUDIES OF THE STRONG MAGNETIC FIELD ACTION ONTHE CORROSION OF RAFM STEELS IN Pb17Li MELT FLOWS, PAMIR 7, 2008

Strong experimental evidence of significant effect of the applied magnetic field on corrosion rate. The underlying physical mechanism has not been fully understood yet

Experiments in Riga (funded by Euratom) Show Strong Effect of the Magnetic Field on Corrosion

(Results for PbLi in Ferritic Steel)

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Need R&D on Corrosion: Modelling and Experiments in MHD Flows Relevant to the Fusion System Environment

• Corrosion includes many physical mechanisms that are currently not well understood (dissolution of the metals in the liquid phase, chemical reactions of dissolved non-metallic impurities with solid material, transfer of corrosion products due to convection and thermal and concentration gradients, etc.).

• We need to better understand corrosion process, including transport and deposition.

• We need new models that can predict corrosion rates and transport and deposition of corrosion products throughout the heat transport system.

– These models need to account for MHD velocity profiles and heat transfer in the blanket and the temperature gradients and complex geometry in the entire heat transport systems.

• More comprehensive experiments are needed.– Need to simulate MHD velocity profiles– Need to simulate the temperature field and temperature gradients in the “hot” and

“cold” sections.– Better instrumentation

• R&D to develop corrosion resistant “barriers” will have high pay off.

• Highest interest is in PbLi systems with both ferritic steel and SiC (FCI).

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MHD Flow

Illustration of Coupling between MHD and heat and mass transfer in blanket flows

Heat Transfer Mass Transfer

ConvectionTritium

transportCorrosion

He Bubbles

formation and their transport

Diffusion Buoyanoy-driven flows

Dissolution and diffusion through the

solid

Interfacial phenomena

Transport of corrosion products

Deposition and aggregation

Tritium Permeation

Dissolution, convection, and diffusion through

the liquid

Coupling through the source / sink term, boundary conditions, and transport coefficients

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Theory/Modeling/Data

BasicSeparateEffects

MultipleInteractions

PartiallyIntegrated

Integrated

Property Measurement

Phenomena Exploration

Non-Fusion Facilities

Science-Based Framework for FNST R&D involves modeling and experiments in non-fusion and fusion facilities

Design Codes

Component

•Fusion Env. Exploration•Concept Screening•Performance Verification

Design Verification & Reliability Data

Testing in Fusion Facilities

(non neutron test stands, fission reactors and accelerator-based neutron sources)

• Experiments in non-fusion facilities are essential and are prerequisites to testing in fusion facilities

• Testing in Fusion Facilities is NECESSARY to uncover new phenomena, validate the science, establish engineering feasibility, and develop components

MHD flows in fusion context are characterized by very unique effects not seen in ordinary fluid dynamics

• High interaction parameter ~103 to 105

(ratio Magnetic / Inertial Forces)– Inertia forces are small compared

with electromagnetic forces, except in some thin layers

• Result: Joule dissipation associated with the strong magnetic field induces a strong flow anisotropy, ultimately leading to a quasi-2D state.

MTOR Thermofluid/MHD facility at UCLA

1 m/s flow, B = 0 B = 1.2 T

Liquid metal free surface flow experimentMagnetic field suppresses short wavelength surface oscillations and consolidates them into larger surface disturbances aligned with the field

Ying (UCLA)

Slide 29

• Fusion heat flux requirements rival that of rocket engines, but must operate for long periods of time

• Effects of thermal cycling are particularly worrisome for ITER operation, where many pulses of the burning plasma are required

Fusion plasma facing components must survive for long operating time with severe heat fluxes

PMTF-1200 high heat flux facility at SNL

High heat flux experiments Repeated high heat flux and thermal cycle survivability tests on mockups of the first wall for ITER, both EU (right column) and US (left column) samples survived 12,000 cycles at 0.875 MW/m2 and 1000 cycles at 1.4 MW/m2 (Ulrickson, SNL)

Irradiation experiments in fission reactors to test tritium release/retention in lithium ceramics

• Using lithium bearing ceramics is one option, often in the form of small pebble beds

• But this material must release tritium and resist damage by neutrons and extreme thermal conditions

• Fission experiments are being used to explore this behavior prior to testing in fusion

Ceramic breeder irradiation experimentsUnit cells of Beryllium and Li4SO4 have been tested in the NRG reactor in Petten, Netherlands to investigate tritium release characteristics and combine neutron and thermomechanical damage to ceramic breeder and beryllium pebble beds

077-05/rs

3131

Testing Blankets in the fusion environment is Necessary: Combined effects of Radiation, Surface Heat flux, Nuclear Heating & gradients, Magnetic field & gradients, etc can be reproduced only in a fusion facility.

PbLi flow is strongly influenced by MHD interaction with plasma confinement field and buoyancy-driven convection driven by spatially non-uniform volumetric nuclear heating

This MHD flow and convective heat transport processes determine the temperature and thermal stress of SiC FCI

The FCI temperature and thermal stress coupled with early-life radiation damage effects in ceramics affect deformation, cracking, and properties of the FCI

Cracking and movement of the FCIs will strongly influence MHD flow behavior by opening up new conduction paths that change electric current profiles

Simulation of 2D MHD turbulence in PbLi

flow

FCI temperature, stress and deformation

Resulting temperature field also strongly couples to phenomena such as tritium transport and permeation, and corrosion

Courtesy of S. Smolentsev

Example: MHD flow & FCI behavior are highly coupled in a complex fusion environment

32

ITER Provides Substantial Hardware Capabilities for Testing of Blanket System

Vacuum Vessel

Bio-shield

A PbLi loop Transporter located in

the Port Cell Area

He pipes to TCWS

2.2 m

TBM System (TBM + T-Extrac, TBM System (TBM + T-Extrac, Heat Transport/Exchange…)Heat Transport/Exchange…)

Equatorial Port Plug Assy.

TBM Assy

Port Frame

ITER has allocated 3 ITER equatorial ports (1.75 x 2.2 m2) for TBM testing

Each port can accommodate only 2 modules (i.e. 6 TBMs max)

Fluence in ITER is limited to 0.3MW-y/m2 . We have to build another facility, for FNST development

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THREE Stages of FNST Testing in Fusion Facilities are Required Prior to DEMO

Sub-Modules/Modules

Stage I

Fusion “Break-in” & Scientific Exploration

Stage II Stage III

Engineering Feasibility & Performance

Verification

Component Engineering Development &

Reliability Growth

Modules Modules/Sectors

D E M O

1 - 3 MW-y/m2 > 4 - 6 MW-y/m2

0.5 MW/m2, burn > 200 s1-2 MW/m2,

steady state or long pulseCOT ~ 1-2 weeks

1-2 MW/m2,steady state or long burn

COT ~ 1-2 weeks

0.1 - 0.3 MW-y/m2

Role of ITER TBM

Role of FNF (CTF/VNS)

ITER is designed to fluence < 0.3MW-y/m2. ITER can do only Stage I

A Fusion Nuclear Facility, FNF is needed , in addition to ITER, to do Stages II (Engineering Feasibility) and III (Reliability Growth)

FNF must be small-size, low fusion power (< 150 MW), hence, a driven plasma with Cu magnets.

Example of Fusion Nuclear Facility (FNF) Device Design Option : Standard Aspect Ratio (A=3.5) with demountable TF coils (GA design)

• High elongation, high triangularity double null plasma shape for high gain, steady-state plasma operation

Challenges for Material/Magnet Researchers:

• Development of practical “demountable” joint in Normal Cu Magnets

• Development of Inorganic Insulators (to reduce inboard shield and size of device)

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Lessons learned:The most challenging problems in FNST

are at the INTERFACES• Examples:

– MHD insulators

– Thermal insulators

– Corrosion (liquid/structure interface temperature limit)

– Tritium permeation

• Research on these interfaces must integrate the many technical disciplines of fluid dynamics, heat transfer, mass transfer, thermodynamics and material properties in the presence of the multi-component fusion environment (must be done jointly by blanket and materials researchers)

3636

Summary• Fusion is the most promising long-term energy option

– renewable fuel, no emission of greenhouse gases, inherent safety

• The blanket must simultaneously achieve tritium breeding and power extraction at high temperature in a multi-component fusion environment (magnetic field, radiation field, surface heat flux, bulk heating) with strong gradients. This results in new phenomena and synergistic effects that can not be anticipated from simulations and separate-effect tests.

• Fluid dynamics, heat & mass transfer play important role in R&D for blankets and other plasma-facing components. Other important disciplines are neutronics, radiation effects, structural mechanics.

• LM Blankets are most promising, but their potential is limited by MHD effects. Innovative concepts must continue to be proposed and investigated

• Modeling and experiments for blanket and PFC are challenging because of complex geometry, multi component fields with gradients, and the inability to simulate bulk heating in the lab without neutrons. Significant progress has been made in 3-D modeling and in laboratory experiments.

• 7 nations started construction of ITER to demonstrate the scientific and technological feasibility of fusion energy. ITER will have first DT plasma in ~2026

• The most challenging Phase of Fusion development still lies ahead. It is the development of Fusion Nuclear Science and Technology (FNST)

– ITER, limited fluence, addresses only initial Stage of FNST testing– In addition to ITER, a Fusion Nuclear Facility (FNSF) is required to develop FNST.