REALIZATION OF FUSION AS THE ULTIMATE ENERGY SOURCE FOR HUMANITYMohamed AbdouDistinguished Professor of Engineering and Applied ScienceDirector, 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 onExperimental Heat Transfer, Fluid Mechanics and Thermodynamics

Krakow, Poland June 28-July 3, 2009

*REALIZATION OF FUSION AS THE ULTIMATE ENGERGY SOURCE FOR HUMANITY

077-05/rs

*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 reaction rate and high Q value. The World Program is focused on the D-T CycleIllustration from DOE brochureE = mc2 17.6 MeV80% of energy release (14.1 MeV)Used to breed tritium and close the DT fuel cycleLi + n T + He Li in some form must be used in the fusion system 20% of energy release (3.5 MeV)DeuteriumNeutronTritiumHelium

Incentives 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 gasesNo risk of a severe accidentNo long-lived radioactive waste

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

*Fusion Research is about to transition from Plasma Physics to Fusion Science and Engineering1950-2010The Physics of Plasmas

2010-2035The Physics of Fusion Fusion Plasmas-heated and sustainedQ = (Ef / Einput )~10ITER (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)The World Fusion Program has a Goal for a Demonstration Power Plant (DEMO) by ~2040(?)Plans for DEMO are based on Tokamaks

*ITERThe 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 energyJET~15 mBy Comparison, JET~10 MW~1 secPassively CooledWill use D-T and produce neutrons500MW fusion power, Q=10Burn times of 400sReactor scale dimensionsActively cooled PFCsSuperconducting magnets

*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 plasmaSuperconducting, Nb3Sn/Cu/SSMax. field: 11.8T

6 Poloidal Field (PF) coils position and shape the plasmaSuperconducting, NbTi/Cu/SSMax. field: 6TCentral Solenoid (CS) coil induces current in the plasmaSuperconducting, Nb3Sn/Cu/alloy908Max. field: 13.5TTF coil case provides main structure of the magnet system and machine core18 Correction coils correct error fields Superconducting, NbTi/Cu/SS Max. field < 6TStored 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 ITERITER Operations: 34% Europe 13% Japan 13% U.S. 10% China 10% India 10% Russia 10% S. KoreaBeing plannedFusion Nuclear Science &Technology Testing Facility (FNSF/CTF/VNS)

*Coolant for energy extractionFirst WallShieldVacuum vesselMagnetsTritium breeding zoneThe primary functions of the blanket are to provide for: Power Extraction & Tritium BreedingDTLithium-containing Liquid metals (Li, PbLi) are strong candidates as breeder/coolant

*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 Flux Components (divertor, limiter, rf/PFC element, etc)3. Vacuum Vessel & Shield Components Fusion Power & Fuel Cycle TechnologyThe location of the Blanket inside the vacuum vessel is necessary but has major consequences:a- many failures (e.g. coolant leak) require immediate shutdownb- repair/replacement take long time

*Fusion environment is unique and complex:multi-component fields with gradientsRBpBT0BInnerEdgeOuterEdgePlasmaWidthNeutron and Gamma fluxesParticle fluxesHeat 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 directionMulti-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)

*Fusion Nuclear Science & Technology IssuesTritium Supply & Tritium Self-SufficiencyHigh Power DensityHigh TemperatureMHD for Liquid Breeders / CoolantsTritium Control (Extraction and Permeation)Reliability / Maintainability / AvailabilityTesting in Fusion FacilitiesChallenging

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

MHD Characteristics of Fusion Liquid Breeder Blanket Systems

**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 materialsPerfect insulators make the net MHD body force zeroBut 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 gradientsSelf-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 zeroConducting walls Insulated wallsImpact of MHD and no practical Insulators :No self-cooled blanket optionSelf-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?

**

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

EU mainline blanket designAll energy removed by separate Helium coolantThe 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 manifoldsB- 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)

*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 heliumBreeding zone is self-cooled Structure and Breeding zone are separated by SiCf/SiC composite flow channel inserts (FCIs) thatProvide thermal insulation to decouple PbLi bulk flow temperature from ferritic steel wallProvide electrical insulation to reduce MHD pressure drop in the flowing breeding zoneFCI does not serve structural functionPb-17Li exit temperature can be significantly higher than the operating temperature of the steel structure High Efficiency

077-05/rs

**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 issuesUnique 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 insulationCourtesy of Munipalli et al.(Ha=1000; Re=1000; =5 S/m, cross-sectional dimension expanded 10x)

*Buoyancy effects in DCLL blanketDCLL DEMO blanket, USVorticity distribution in the buoyancy-assisted (upward) poloidal flowCaused byand associatedCan be 2-3 times stronger than forced flows. Forced flow: 10 cm/s. Buoyant flow: 25-30 cm/sIn buoyancy-assisted (upward) flows, buoyancy effects may play a positive role due to the velocity jet near the hot wall, reducing the FCI TIn buoyancy-opposed (downward) flows, the effect may be negative due to recirculation flowsEffect on the interface T, FCI T, heat losses, tritium transport

*Corrosion Is A Serious Issue For LM BlanketsAt present, the interface temperature between PbLi and Ferritic Steel (FS) is limited to < 470 C because of corrosionThis 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.

*Macrostructure of the washed samples after contact with the PbLi flowB=0 TB=1.8 TFrom: F. Muktepavela et al. EXPERIMENTAL STUDIES OF THE STRONG MAGNETIC FIELD ACTION ONTHE CORROSION OF RAFM STEELS IN Pb17Li MELT FLOWS, PAMIR 7, 2008Strong experimental evidence of significant effect of the applied magnetic field on corrosion rate. The underlying physical mechanism has not been fully understood yetExperiments in Riga (funded by Euratom) Show Strong Effect of the Magnetic Field on Corrosion (Results for PbLi in Ferritic Steel)

*Need R&D on Corrosion: Modelling and Experiments in MHD Flows Relevant to the Fusion System EnvironmentCorrosion 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 profilesNeed to simulate the temperature field and temperature gradients in the hot and cold sections.Better instrumentationR&D to develop corrosion resistant barriers will have high pay off.Highest interest is in PbLi systems with both ferritic steel and SiC (FCI).

*MHD FlowIllustration of Coupling between MHD and heat and mass transfer in blanket flowsHeat TransferMass TransferConvectionTritium transportCorrosionHe Bubbles formation and their transportDiffusionBuoyanoy-driven flowsDissolution and diffusion through the solidInterfacial phenomenaTransport of corrosion productsDeposition and aggregationTritium PermeationDissolution, convection, and diffusion through the liquidCoupling through the source / sink term, boundary conditions, and transport coefficients

*Theory/Modeling/DataBasicSeparateEffectsMultipleInteractionsPartiallyIntegratedIntegratedProperty MeasurementPhenomena ExplorationNon-Fusion FacilitiesScience-Based Framework for FNST R&D involves modeling and experiments in non-fusion and fusion facilitiesDesign CodesComponentFusion Env. ExplorationConcept ScreeningPerformance VerificationDesign Verification & Reliability DataTesting 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 facilitiesTesting 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 layersResult: 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 UCLA1 m/s flow, B = 0 B = 1.2 TLiquid 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 *Fusion heat flux requirements rival that of rocket engines, but must operate for long periods of timeEffects of thermal cycling are particularly worrisome for ITER operation, where many pulses of the burning plasma are requiredFusion plasma facing components must survive for long operating time with severe heat fluxesPMTF-1200 high heat flux facility at SNLHigh 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 ceramicsUsing 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

**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 profilesSimulation of 2D MHD turbulence in PbLi flowFCI temperature, stress and deformationResulting temperature field also strongly couples to phenomena such as tritium transport and permeation, and corrosionCourtesy of S. SmolentsevExample: MHD flow & FCI behavior are highly coupled in a complex fusion environment

*ITER Provides Substantial Hardware Capabilities for Testing of Blanket SystemVacuum Vessel Bio-shield A PbLi loop Transporter located in the Port Cell Area He pipes to TCWS2.2 mTBM System (TBM + T-Extrac, Heat Transport/Exchange)ITER has allocated 3 ITER equatorial ports (1.75 x 2.2 m2) for TBM testingEach 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

*THREE Stages of FNST Testing in Fusion Facilities are Required Prior to DEMOSub-Modules/Modules Stage IFusion Break-in & Scientific ExplorationStage IIStage III Engineering Feasibility & Performance VerificationComponent Engineering Development & Reliability GrowthModulesModules/SectorsD E M O1 - 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 weeks1-2 MW/m2,steady state or long burnCOT ~ 1-2 weeks0.1 - 0.3 MW-y/m2Role of ITER TBMRole 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 operationChallenges for Material/Magnet Researchers: Development of practical demountable joint in Normal Cu MagnetsDevelopment of Inorganic Insulators (to reduce inboard shield and size of device)

*Lessons learned:The most challenging problems in FNST are at the INTERFACESExamples:

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)

**SummaryFusion is the most promising long-term energy optionrenewable 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 investigatedModeling 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 ~2026The 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 testingIn addition to ITER, a Fusion Nuclear Facility (FNSF) is required to develop FNST.

**The baseline parameters for QPS are 0.9 m major radius, avg minor radius of .35 m and a 1 T magnetic field

We desire a factory assembled unit, consisting of the stellarator core in and attempt****************