Technical Strategies for Pressure Drop Reduction in LM Blankets

N. B. Morley, S. Smolentsev,

B. Pint, D.-K. Sze, S. Malang

APEX/TBM Meeting

February 23, 2004

Main Thermofluid Issue for Self-Cooled Liquid Metals

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

Feasibility:

Inboard high field regions may require pressures greater than allowable pipe limits

MHD pressure drop reduction strategies

• Lower K– Insulator coatings/Laminated walls– Flow channel inserts– Elongated channels with anchor links

or other design solutions

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

velocity required for first wall/breeder zone cooling– High temperature difference operation to lower mass flow

• Lower B,L – Outboard blanket only (ST)

• Lower (molten salt)

2UBKLP lK represents a measure of relative conductance of induced current closure paths

Break electrical coupling to thick

load bearing channel walls

Force long current path

DEMO Designs using LMs

• PbLi breeder with separate coolant • Dual coolant PbLi with flow channel inserts• Lithium/Vandium with insulator coatings or laminated walls• Are there others we should consider??

Evaluation strategy• Look at the state of the MHD issue R&D for existing DEMO

designs using LMs (this presentation)• Judge relative feasibility/attractiveness for selection • Suggest and discuss possible US roles in developing

DEMO blankets for pre-ITER R&D and ITER testing • Choose path

Dual Coolant Lead-Lithium Concepts with Flow Channel Inserts (FCIs)

• Cool FW and structure with separate coolant – He• FCIs decouple vB emf in flow from current closing

paths in the thick channel walls • FCIs decouple bulk flow temperature from wall

temperature• Many attractive features for MHD pressure drop

reduction – Current closing path conductance determined by the properties

of the insert, not the channel wall– No high speed Pb-Li flow needed for FW cooling– High bulk temperature rise of Pb-Li due to thermal insulation by

FCIs allows very low velocity in blanket region– Electrical conductivity of Pb-Li is roughly 3 small than Li

ARIES-ST Dual Coolant Design (FED, 65, 2003)

Features:• ST Geometry requires no inboard

blanket• Outboard poloidal flow blanket

has two-pass Pb-Li flow

EU Advanced Dual Coolant DEMO Blanket (FED, 61-62, 2002 or FZKA 6780)

Features:• Inboard/Outboard poloidally

segmented blanket modules, each with two-pass Pb-Li flow

MHD pressure drop dominated by 3D

effects in EU Design• Slow flow in poloidal

channels with FCIs have very small pressure drop ~10-4-10-2 MPa/m (depending on flow velocity and local field)

• 3D pressure drop to distribute flow from manifolds to poloidal channels estimated at 2 MPa on inboard (1MPa ouboard)

• 3D pressure drop due to field entry effects estimated at ~.2MPa

• No experiments or models similar to coaxial flow manifold channel

What are issues for SiC FCIs

a) Electrical and thermal conductivity of the SiC should be as low as possible to avoid velocity profiles with side-layer jets and excess heat transfer to the He structure coolant.

b) The inserts have to be compatible with Pb-17Li at temperatures up to 700-800 °C

c) Liquid metal must not “soak” into pores of the composite in order to avoid increased electrical conductivity and high tritium concentrations. In general “sealing layers” are required on all surfaces of the inserts.

– Even surface layers (in surface pores for instance) > 10 micron will affect pressure drop

– Even if change in insert effective conductivity is modest from pressure drop point of view it could affect flow balance greatly – DKs point for FCIs, coatings and laminated walls.

d) There are no primary stresses in the inserts. However, secondary stresses caused by temperature gradients must not endanger the integrity under high neutron fluences.

Partly extracted from EU Dual Coolant design report

Electrical Conductivity of SiC

• Typical value quoted for Cerasep version as 500 -1m-1 will result in side-layer jet formation and near stagnation in core

• Several orders of magnitude variation of conductivity with technique and temperature is seen

• No information on effect of radiation

Corresponds to 1 -1m-1

Most recent Pb-Li / SiC data from ORNL* shows no penetration at elevated temperatures – in

agreement with previous studies in Europe

Specimens of dense monolithic SiC, made by chemical vapor deposition (CVD), were exposed to Pb-17Li for 1000h in isothermal capsule tests.

• After 1000h at 800°C, no evidence of reaction or wetting between SiC and Pb-17Li was observed.

• No specimen mass change was observed after 1000h at 1100°C, but there was evidence of limited wetting.

• Nevertheless, the results suggest that SiC is compatible with Pb-17Li to at least 1100°C in a static environment.

Question: what experiment is needed to ultimately demonstrate compatibility?

• Flowing test with thermal gradients – Malang’s point

*(Pint et al., ICFRM, Japan, Dec 2003)

Questions for the experts…• Would you expect the wetting or attack of PbLi on SiC to

increase if the system was pressurized? flowing?– Pint: I don't think flow should affect wetting but pressure might. One

thing that I tried to emphasize is that an incubation period has been observed for Hg wetting. For longer exposures at a given temperature, wetting can change with time, likely due to dissolution of a native oxide.

– Sze: Pressure will not change the wetting characteristics, but flow might. I saw this on our SS/Li loop experiment at U. Wisconsin.

• Can the SiC insert shapes currently be fabricated? Could such inserts be ready for ITER testing?– Pint: DOE/Solar Turbines/BFGoodrich are making 1-2m diameter

combustor liners of SiC/SiC so I think the channel inserts could be fabricated.

– Sze: This will not be easy also. KfK worked on this possibility and gave up.

– Malang: KfK manufactured sandwich type inserts from Ferritic steel plates with alumina, but never tried SiC

MHD issues for EU-HCLL

• MHD effects will certainly be present, but probably are not the major issues– Flow distribution and

pressured drop likely to be affected by MHD forces

– MHD modeling of flow profiles and natural convection might be needed to predict interface temperatures, heat transfer, T permeation, etc.

• Issues of steel compatibility and tritium permeation are somewhat common issues with Dual Coolant blanket

Possible US role in PbLi Dual-Coolant Development and Testing

• Adopt Dual-Coolant as a US DEMO option. • Continue to evolve the design possibly in collaboration with EU

(evaluate issues like effect of velocity profiles, flow balancing)• Coordinate with EU on issues of mutual interest for tritium permeation,

material compatibility, etc.

Pre-ITER R&D related to MHD issue • Definitive SiC/PbLi compatibility tests and SiC property tests for low

conductivity• Fabrication development and thermo-mech tests for SiC inserts• MHD flow experiments regarding unknown dual coolant flow elements

(experiments not necessarily with SiC FCI)– Coaxial hot/cold manifolds, Flow distribution from manifolds to poloidal channels– Long term behavior of FCI straight and overlap regions

• Continue to develop and benchmark predictive capability for complex shaped flow elements at high Hartmann number

Collaborate with EU* to introduce Dual Coolant specific test modules in ITER HCLL TBM

Possible ITER Testing• Place SiC (or substitute) inserts in PbLi feed lines for EU

HCLL TBM to observe– Pressure drop in straight and FCI overlap regions

– SiC interaction with PbLi over long term operation, in high field and low fluence

• Replace single or multiple breeder unit in EU HCLL TBM with special designed dual-coolant breeder unit to study:– Pressure drop in complex flow distribution system

– Thermal stress effects and reliability of inserts

– SiC interaction with PbLi over long term operation and low fluence

• Support EU on testing issues of joint interest: tritium breeding and permeation, ferritic steel compatibility, etc.

*Provided EU people are interested and EU program receptive

Liquid Lithium Breeder

• Configuration:– Self-cooled– Vanadium alloy

structure

• Reference Designs:– Blanket Comparison

and Selection Study– ARIES-RS– Russian DEMO?,

Japan??

ARIES-RS Outboard Module

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

• Tolerable crack fraction appears to be quite low, well below that achievable with real coatings

• Suggestion has been made to move to laminated wall systems of OX/MET

(Following presentation by Zinkle will focus on these points)

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)

Pipe

Stre

ss (M

Pa)

Base Case

Crack Fraction, f = 1e-3

Crack Fraction, f = 1e-4

Crack Fraction, f = 1e-5

Crack Fraction, f = 1e-6

ITER FW ARIES-RS FW

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

LM-MHD pressure drop window for inboard insulated walled channels

1

2

221

)NWL(

f

wcw

p

w

fa

tt

Tc

BLS

• Can stable coatings be found? What is the current assessment?• What is the real tolerance to coating imperfections and lithium

penetration on pressure drop• Should we consider alternatives, like laminated walls or flow

channel inserts to remove direct contact of the Li with the insulator? DK comment on flow balance

• Is V alloy temperatures likely to be limited in temperature to similar levels as ferritic steel? Should we consider switching this concept to ferritic steel structure – more likelihood of coatings?

• Can 3D pressure drops be accurately evaluated, are they acceptable even with effectively insulated or thin conducting walls?

MHD related issues* for self-cooled lithium

*(Other issues related to Vanadium alloy development are not covered)

Questions for the experts

• Can multiple insulator/metallic layer laminates be fabricated?– Russians: had difficulty CVD coating dense enough metallic

layers onto AlN coatings to prevent penetration of Li (FED, Vol. 61-62, p. 739)

– Pint: Jankowski at LLNL has deposited multilayer coatings before, Y2O3 and Ta on Ta-10W. It probably becomes more difficult on complex shapes but we need to test the concept first. I think coating coupons with 2 layer or 4 layer structure OX/MET/OX/MET is trivial. (right now LLNL has no budget)

– Sze: Making a sample, few cm2 area, with a laminated wall structure, is not an issue. Making this type of structure for fusion blanket, with the complicated geometry, is the issue.

Possible US role in Self-Cooled Li Development and Testing

• Adopt self-cooled Li as a US DEMO option. Decide on V or FS.• Continue to evolve a design (based on ARIES-RS?) possibly in

collaboration with RF, Japanese Universities (JU), South Korea, China. Design issues: coatings, laminates?; Flow balancing strategy,…

• Coordinate with RF, JU, SK, China on issues of mutual interest for coating development, MHD analysis and testing

Pre-ITER R&D related to MHD issue • Coating/laminated wall technology must be developed for

increasingly large components• Partially integrated system MHD testing – coated components, Li

flow and mass transfer, surface heating, magnetic field. – Effects on pressure drop and flow balancing from metal layer or coating

failure or significant corrosion

• Continue to develop and benchmark predictive capability for complex shaped flow elements at high Hartmann number

Collaborate with RF, JU, South Korea, China TBM program to maximize MHD testing possibilities in

ITER

Possible ITER MHD Testing (only small Li volume permitted in ITER)

• Series of small modules to test integrated MHD pressure drop, corrosion, flow balancing inter-related effects – Highly thermally stressed or cycled coatings– Radiation field effects– Long term corrosion effects

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 2T gap magnet also useful for long 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