Fusion Science and Technology

Mohamed Abdou, Neil Morley, Alice Ying

Mechanical and Aerospace Engineering Dept.CESTAR: Center for Energy Science and Technology Advanced Research

Presentation at KAIST/UCLA Joint Workshop, January 13-14, 2005

WEB SITE: http://www.fusion.ucla.edu/

Fusion Science and Technology at UCLA• Fusion Research is exciting and active worldwide

• UCLA has strong research programs in plasma physics, fusion science and technology

• The largest part of the Fusion Science and Technology Research at UCLA is in the Mechanical and Aerospace Engineering Department

• UCLA leads the US program in Fusion Nuclear Technology

• We already have strong international collaborative programs with Europe, Japanese Universities, JAERI, Korea (KAIST and KAERI), China, and Russia

• Our research involves many technical disciplines: fluid mechanics, heat transfer, MHD, tritium transport, neutronics, materials, structural mechanics

• We have constructed world-class experimental facilities. Many students do their Ph.D. research in these facilities. The facilities also attract important international collaborations

Introduction

Incentives for Developing Fusion• Fusion powers the Sun and the stars

– It is now within reach for use on Earth

• In the fusion process lighter elements are “fused” together, making heavier elements and producing prodigious amounts of energy

• Fusion offers very attractive features:– Sustainable energy source

(for DT cycle; provided that Breeding Blankets are successfully developed)

– 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

The Deuterium-Tritium (D-T) Cycle

• World Program is focused on the D-T cycle (easiest to ignite):

D + T → n + α + 17.58 MeV

• The fusion energy (17.58 MeV per reaction) appears as Kinetic Energy of neutrons (14.06 MeV) and alphas (3.52 MeV)

• Tritium does not exist in nature! Decay half-life is 12.3 years

(Tritium must be generated inside the fusion system to have a sustainable fuel cycle)

• The only possibility to adequately breed tritium is through neutron interactions with lithium– Lithium, in some form, must be used in the fusion system

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 Concepts(many concepts proposed worldwide)

A. Solid Breeder Concepts– Always separately cooled

– Solid Breeder: Lithium Ceramic (Li2O, Li4SiO4, Li2TiO3, Li2ZrO3)

– Coolant: Helium or Water

B. Liquid Breeder ConceptsLiquid breeder can be:

a) Liquid metal (high conductivity, low Pr): Li, or 83Pb 17Li

b) Molten salt (low conductivity, high Pr): Flibe (LiF)n · (BeF2), Flinabe (LiF-BeF2-NaF)

B.1. Self-Cooled– Liquid breeder is circulated at high enough speed to also serve as coolant

B.2. Separately Cooled– A separate coolant is used (e.g., helium)

– The breeder is circulated only at low speed for tritium extraction

B.3. Dual Coolant– FW and structure are cooled with separate coolant (He)

– Breeding zone is self-cooled

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)

Liquid Breeder Blanket Concepts1. Self-Cooled

– Liquid breeder circulated at high speed to serve as coolant

– Concepts: Li/V, Flibe/advanced ferritic, flinabe/FS

2. Separately Cooled– A separate coolant, typically helium, is used. The breeder is

circulated at low speed for tritium extraction.

– Concepts: LiPb/He/FS, Li/He/FS

3. Dual Coolant– First Wall (highest heat flux region) and structure are cooled

with a separate coolant (helium). The idea is to keep the temperature of the structure (ferritic steel) below 550ºC, and the interface temperature below 480ºC.

– The liquid breeder is self-cooled; i.e., in the breeder region, the liquid serves as breeder and coolant. The temperature of the breeder can be kept higher than the structure temperature through design, leading to higher thermal 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

BjgVVVV

11

)( 2pt

-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

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

-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

ITER

4 of 7 Central Solenoid modules

15% of port-based diagnostic packages

44% of ICRH Antenna, plus all transmission lines,

RF-sources, power supplies

Start-up gyrotrons,all transmission lines,and power supplies

BaffleRoughing pumps,

standard components

Tokamak exhaustprocessing system

Cooling for Divertorand Vacuum VesselPellet Injector

Steady-statepower supplies

U.S. In-kind Contributions to ITER

Test Blanket Module

ITER Provides the First Integrated Experimental Conditions for Fusion Technology Testing

• Simulation of all Environmental Conditions

Neutrons Plasma Particles

Electromagnetics Tritium

Vacuum Synergistic Effects

• Correct Neutron Spectrum (heating profile)

• Large Volume of Test Vehicle

• Large Total Volume, Surface Area of Test Matrix

• Solid Breeders– He/SB/Be/FS: All parties are strongly interested– H2O/SB/Be/FS: Only Japan (some interest from China)

• Liquid Breeders– He/LiPb/FS (Separately cooled): EU lead (one of two main concepts for

EU, interest from other parties)– Dual Coolant (He/LiPb/FS with SiC): US lead, strong interest from EU

and other parties– Li/V (Self-cooled): Russia is main advocate (but no significant

resources on R&D!)– Molten Salts: US and Japanese Universities want the option to decide

later whether to test– He/Li/FS: Korea’s proposal

Blanket Concepts for ITER-TBM Selected by the Various Parties

Blanket Testing in ITER is one of ITER’s Key Objectives

Strong international collaboration among the ITER Parties is underway to provide the science basis and engineering capabilities for ITER TBMs

Bio-Shield Plug

Cryostat Plug

Transporter

Cryostat Extension

TBM Frame & Shield Plug

Breeder Concentric

Pipe

Drain Pipe

FW

US Solid breeder submodule

EU HCLL Test Module

Conceptual Liquid Breeder Port Layout and Ancillary equipment

UCLA Activities

UCLA Program in Fusion Engineering Research

Current UCLA Research Activities– ITER Test Blanket Module R&D– Molten Salt Thermofluid MHD (Jupiter-II)– Solid Breeder / SiC Thermomechanics (Jupiter-II)– Solid Breeder / Steel Thermomechanics (IEA)– ITER Basic Machine and Procurement Package

Support– Free Surface MHD Flows for Plasma Facing

Components– IFE Chamber Clearing Study

Experiments, Microscopic and Macroscopic Modeling efforts simultaneously underway to Understand and Predict Solid Breeder

Blanket Pebble Bed Thermomechanics Interactions

Radial distance (mm)

No

rma

lStr

ess

(MP

a)

0 10 20 30 40 50-2.5

-2.25

-2

-1.75

-1.5

-1.25

-1

-0.75

-0.5

-0.25

0

0.25

0.5

Temp = 450oCTemp = 650oCTemp = 822oC

Radial distance (mm)

No

rma

lStr

ess

(MP

a)

0 10 20 30 40 50-2

-1.5

-1

-0.5

0

0.5

1

Time = 0 hrTime = 2 hrTime = 24 hrTime = 48 hr

Stress relaxed as creep initiatedStress magnitude profiles at different times

Stress exerted on the wall at different bed temperatures

MARC calculations

MARC calculations

Solid breeder pebbles after the tests

107

108

109

0 0.005 0.01 0.015 0.02 0.025

Time = 0 minutes Time = 2000 minutes

Container Radius (m)

Average stress exerted on the particles at initial time and at time 2000 minutes

Test Article for Deformation Study

DEM calculations

Force distribution inside the particles with 1% compressive strain

IEA collaboration on solid breeder pebble bed time dependent thermomechanics interactions/deformation

research Primary Variables• Materials• Packing• Loadings• Modes of operation

Irradiation Effect(NRG)

Primary & Secondary Reactants:• Temperature magnitude/ gradient• Differential thermal stress/contact pressure• Plastic/creep deformation• Particle breakage• gap formation

Goal:Performance/Integrity prediction & evaluation

Partially integrated out-of-pile and fission reactor tests (NRG,ENEA)

Finite Element Code (ABQUS, MARC)

(NRG, FZK, UCLA)

Discrete Element Model (UCLA)

Design Guideline and Evaluation (out-of-pile & in-pile tests, ITER TBMs)

Database Experimental Program

(FZK, JAERI, CEA,UCLA)

Thermo-physical and Mechanical PropertiesConsecutive equations

Single/multiple effect experiments(NRG, UCLA)

UCLA is collaborating on HIMAG 3D - a complex geometry simulation code for free surface MHD flows

Simulations are crucial to both understanding phenomena and exploring possible flow option for NSTX Li module

Problem is challenging from a number of physics and computational aspects requiring clever formulation and numerical implementation

Unstable MHD velocity profiles in gradient magnetic fields breakdown into instability

Complex geometry: Free surface flow

around cylindrical penetration

Complex geometry MHD codes already being applied to DCLL blanket with SiC

Flow Channel Inserts• 2D and 3D codes

(developed for Liquid walls) have been modified for DCLL

• Initial results show strong sidelayer jets at SiC = 500 S/m with current DCLL design

• 2D and 3D codes give conflicting results concerning flow in the “stagnant” gap region.

• Code improvements and debugging, and continued simulations planned for FY05.

Slice from 3D Simulation

Velocity profile from2D Simulation

Strong negative flow jet near pressure equalization slot not seen in 3D simulation

Gap corner jets not seen in 2D simulation

UCLA MTOR can be for basic flow physics, free surface and TBM module

simulation experiments

Large magnetic volume for complex geometry modules

Higher field smaller volume regions for higher MHD interaction experiments

30 liter gallium alloy flowloop

FC#1

FC#2 MTOR LM-MHD Facility

Turbulent fluctuations organize into 2D structures with vorticity along the magnetic field

Corner vortices and small surface disturbances suppressed Flow can Pinch-IN in field gradients and separate from the wall Drag can be severe, slowing film down by 2x or 3x

B

Experiments on film flows show formation of 2D turbulence structures

B

U

Sophisticated 2-D neutronics analysis shows testing objective can be achieved for a proposed NT TBM

0

1 10-5

2 10-5

3 10-5

4 10-5

5 10-5

0 10 20 30 40 50 60 70

Distance from Frame, cm

Left Configuration Right Configuration

Layer#

Layer#

1

2

3

4

5

6

7

8

9

1

3

2

4

5

6

3

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80

Left TBM WallBe Layer-Left Config.Left VCP-Left Config.Br1Right TBM WallBe Layer- MiddleBe-Rt. SubmduleBe Layer-Rt. Config.Rt. VCP- Left Config.Left VCP-Rt. Config.Rt. VCP-Rt. Config.

Toroidal Distance from Frame, cm

Depth = 42 mm behind FW

Breeder (Lft. Config.)

Be (Rt. Config.)

Proposed NT TBM

JA TBMTritium production profiles are nearly flat over a reasonable distance in the toroidal direction allowing accurate measurements be performed

Finding:Flat nuclear heating and tritium production profiles allow two designs to be evaluated in a ¼ port submodule

Pulsed electro-thermal plasma gun facility provides extreme high heat flux capability for IFE super-heated vapor condensation study

Condensed steel droplets on top of deposited film

Droplet size ~ 1 to 2 m

Condensation characterization from super-heated vapor (for Z-pinch)

Electrical network system provides a pulsed energy source simulating the pellet explosion for

rapid vapor generation

Expansion chamber and diagnostics for super-heated vapor consideration studies

Vapor density decays exponentially with a time constant of 6.58 ms in the range between 5x1017 cm-3 and 2x1015

cm-3

Time 0

820 s

1640 s

Frame sequences recorded with high speed camera - 10,000 frames per second

and shutter speed of 100 ms

Vapor pressure decay curve

Goal:

assessing chamber assessing chamber clearing issues in clearing issues in Inertial Fusion Inertial Fusion Energy systemsEnergy systems

Possibilities for Collaboration

Excellent opportunities exist for collaboration between US and Korea on

fusion engineering

• US has extensive experience in fusion blanket systems developed over 30 years

• US has focused blanket R&D on key areas of blanket feasibility

• Korea has strong background in fission and now fusion technology systems

• Korea has strong industrial and manufacturing capabilities

• Collaboration possibilities are numerous, especially on development and deployment of ITER TBMs of joint interest.

Possibilities for US-Korea Collaboration on Helium-Cooled Ceramic Breeder

Blankets• Development and characterisation of

ceramic breeder and beryllium pebbles• Thermo-mechanics of pebble beds• Tritium release characteristics of

ceramic breeders and beryllium• Beryllium behaviour under irradiation• Helium cooling technology• Prototypical mock-up testing in out-of-

pile facility• In-pile testing of sub-modules• Development of instrumentation

Possibilities for US-Korea Collaboration on Liquid Metal*

Breeder Blankets• Fabrication techniques for SiC Inserts• MHD and thermalhydraulic experiments on SiC flow

channel inserts with Pb-Li alloy• Pb-Li and Helium loop technology and out-of-pile test

facilities• MHD-Computational Fluid Dynamics simulation • Tritium permeation barriers• Corrosion experiments• Test modules design, fabrication with RAFS, preliminary

testing• Instrumentation for nuclear environment

*Similar possibilities exist also for molten-salt blankets