Thermofluid MHD issues for liquidbreeder blankets and first walls

Neil B. Morley and Sergey Smolentsev

MAE Dept., UCLA

APEX/TBM Meeting

November 3, 2003

Main Thermofluid Issue for Liquid Metals

MHD pressure drop very high for electrically conducting ducts and complex geometry flow elements (especially long, high field, inboard flow channels)

Secondary issues• MHD velocity profile effect on heat transfer and

corrosion profiles• High reactivity (safety and compatibility issue)

Possible solutions to MHD pressure drop issue

• Lower K– Insulator coatings– Flow channel inserts– Laminated wall– Elongated channels with anchor links or other design solutions

• Lower U – Heat transfer enhancement or dual/separate coolant to lower first

wall velocity– High temperature operation to lower mass flow requirements

• Lower B – High beta, low B plasma– Outboard blanket only

• Lower L (this game can only be played on the outboard)• Lower (molten salt)

2UBKL

Pl

K represents a measure of relative conductance of induced current closure paths

Break electrical coupling to thick load bearing channel walls

LM-MHD pressure drop window for outboard bare walled channels

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Magnetic Field (T)

Pip

e S

tres

s (M

Pa)

Base Case

Blanket Thickness = .6 m

Flow Length = 5 m

Bulk T rise = 300 K

NWL = 2.5 MW/m2

ITER FW ARIES-RS FW

Lithium Outboard Base Case - NWL = 5 MW/m2 - Blanket Thickness = 0.4 m - Blanket Length = 7.5 m - Coolant Bulk T rise = 200 K

Tc

BLS

p

w

22)NWL((Sze, 1992)

U ~ .2-.3 m/s

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Magnetic Field (T)

Pip

e S

tres

s (M

Pa)

Base Case

Blanket Thickness = .25 m

Flow Length = 4 m

Bulk T rise = 300 K

NWL = 2.5 MW/m2

ITER FW ARIES-RS FW

Lithium Inboard Base Case - NWL = 5 MW/m2 - Blanket Thickness = 0.2 m - Blanket Length = 6.0 m - Coolant Bulk T rise = 200 K

LM-MHD pressure drop window for inboard bare walled channels

Tc

BLS

p

w

22)NWL( (Sze, 1992)

U ~ .2-.3 m/s

Liquid Lithium Breeder

• Configuration:– Self-cooled– Vanadium alloy

structure

• Reference Designs:– Blanket Comparison

and Selection Study– Tokamak Power

Systems Study– ARIES-RS– Russian DEMO?,

Japan??

Insulator coating solution has been the main focus in US for Li/V

• Coating issues affecting thermofluid performance– What is the crack fraction, size, distribution as a function of time

(self-healing or periodically-healed)– How well does the lithium penetrate small cracks and electrically

contact the pressure bearing wall as a function of time

• Impact on MHD pressure drop

Both issues affect the instantaneous K factor for a flow element and flow distribution between channels will vary

• Impact on local velocity profile

Both issues will affect amount of flow in core and sidelayers and even the direction of local velocity flow near cracks

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Magnetic Field (T)

Pip

e S

tre

ss

(M

Pa

)

Base Case

Crack Fraction = 1e-3

Crack Fraction = 1e-4

Crack Fraction = 1e-5

Crack Fraction = 1e-6

ITER FW ARIES-RS FW

Lithium Inboard Base Case - NWL = 5 MW/m2 - Blanket Thickness = 0.2 m - Blanket Length = 6.0 m - Coolant Bulk T rise = 200 K - Channel width = 5 cm - Wall thickness = 8 mm - Coating thickness = 20 micron

LM-MHD pressure drop window for inboard insulated walled channels

1

2

221

)NWL(

f

wcw

p

w

fa

tt

Tc

BLS

MHD questions for blanket & materials community in evaluation study

• Can stable coatings be found? What is the current assessment?• What is the real tolerance to coating imperfections on pressure drop

with realistic collection of flow elements (straight channels + bends, manifolds, and multiple flow elements + regions of strong field variation) with/without first wall cooling

• How can we characterize coating integrity and Li penetration into flaws for the simplest geometries?– Electrical resistance measurements of good coatings in contact with Li– SEM images– MHD testing of coated pipes– Codes to look at 2 phase MHD behavior in near crack regions to help

characterize crack filling behavior

• Should we consider alternatives, like laminated walls or flow channel inserts to remove direct contact of the Li with the insulator?

• Should tests be planned in ITER even if no coating capable of high field operation has been found?

Liquid Lead-Lithium Breeder

• Configurations:– Self-Cooled, Dual-Coolant,

and Separately-Cooled

– Ferritic steel and/or SiC structure and inserts

• Reference Designs:– Blanket Comparison and

Selection Study

– ARIES-AT (self-cooled with SiC structure ) and ARIES-ST (dual-coolant)

– European TAURO, Dual Coolant, and Separately-cooled concepts

Flow channel inserts are main PbLi pressure drop reduction technique for

dual coolant concept

• Types of Flow Channel Inserts– Insulator layer sheathed in ferritic steel– SiC flow channel inserts

• FCIs will behave similarly to laminated wall in many geometric elements

• Main Thermofluid issues, Pressure drop and velocity profiles:– In and near FCI overlap regions– in and near complex flow elements (manifolds, bends, etc.)– in regions of strong field gradients– near cracked or saturated SiC pores

MHD issues for separately-cooled Pb-Li

• Claim is that there is no feasibility issue for slow flowing Pb-Li. This claim should be looked at closely in the study

• MHD modeling of natural convection with MHD might be needed to help predict interface temperatures, heat transfer, T permeation, and safety evaluations

• Large size natural convection experiments may be needed (Literature on natural convection experiments needs to be reviewed).

• EU plans to field separately cooled Pb-Li modules. Close coordination is desirable.

MHD questions for blanket & materials community in evaluation study

• Work in the 1980s and 90s should be revisited. Is there a need for select element experiments in MTOR or LIMITS? e.g. overlap of FCI pieces, manifolds

• Should new modeling tools can be applied to single design elements and to multiple element and complex geometry module designs with FCI

• What is the materials assessment of fabrication (necessary shapes and hermetic coating) and reliability (permeation of Pb-Li into porous ceramic) of necessary SiC FCI features. What about traditional metal sheathed FCI fabrication and reliability?

• Will EU co-operate / collaborate on aspects of self-cooled Pb-Li breeder zones with FCIs?

• Should Pb-Li MHD submodule be MHD tested in ITER using ferritic steel sheathed inserts, and SiC inserts during later stages if qualified?

LM-MHD Simulation Codes

-10 0 10050100

x

-10

0

10

z

X Y

Z

X Y

Z

3-D unstructured mesh for channel flow with insulator crack, Crack size / Duct size = 1 / 100, Number of cells = 3639060, Number of cells over one crack = 10

Several state-of-the-art codes for studying closed channel

LM-MHD flows

HIMAG: 3-D LM-MHD with unstructured mesh for complex geometry (right)

2-D, 3-D MHD research codes developed at UCLA applicable for certain problems

Arbitrary geometry core flow code by L. Buhler for high Ha,N flows. Very powerful but not applicable to all flows

Ha = 200, N = 1000, Velocity profiles at various downstream locations following the steep magnetic field gradient at x = 0.

Currently MTOR has a 15 Liter Ga-In-Sn flow loop and a 30 Liter volume of alloy available

• Large volume magnetic torus can accommodate large structures (manifolds, modules, etc.) in moderate field (currently ~.5 T, upgradeable to > 1T) and with toroidal field gradients

• Two flux concentrators (FC) currently available for higher field (~1.5T) experiments in 8 cm x 45 cm gap. (Longer gaps possible)

• J2 magnet also useful for longer flow length experiments

• Multiple experiments can be accommodated simultaneously

FC#1

FC#2

MTOR LM-MHD Test Facility

Can be used for studying closed channel or free surface Liquid Metal MHD flows

Ga film flow, B=0 Ga film flow, B=1T

LIMITS Characteristics

• Lithium Volume 60 l• Operating temperature 20-

400 C• Pump Flow rate 0-3 l/s• Magnetic Field

– 0.6 Tesla toroidal

– 0.2 Tesla poloidal

• Diagnostics– Video, IR cameras

– EM flow meter, T