1 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Comments on Corrosion R&D Needs for...

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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Comments on Corrosion R&D Needs for DCLL

B.A. Pint and P.F. Tortorelli

Presented by S.J. Zinkle

Oak Ridge National Laboratory

US ITER-TBM Meeting

Idaho Falls, ID

August 10-12, 2005

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Compatibility in the DCLL system will likely involve multiple materials

• In-vessel TBM – ferritic/martensitic steel, SiC FCI

• External piping– Ni-base superalloy?

• Tritium processing– Refractory alloy??, tritium permeation barrier materials??

• Heat exchanger– Material options??

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Liquid Metal Compatibility is Controlled by several mechanisms

• Dissolution– Numerous phenomena can affect mass transfer across metal-liquid interface,

J=k (C0-C)

• Laminar vs. turbulent flow (including magnetic field effects)

• Solubility temperature dependence

• Impurity and interstitial transfer– Very important for refractory metals (and BCC metals in general)

• Alloying between the liquid metal and solid– Typically eliminated early on in selection process (showstopper)

• Compound reduction– Often most relevant for ceramics (e.g., SiC insert)

• The last three mechanisms can be roughly evaluated using low-cost capsule experiments; the 1st mechanism requires flowing loop tests

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There are two major contributors to dissolution mass transfer

• Static isothermal mechanisms – Capsule tests can provide initial data on solubilities (infinite

dilution steady-state approximation)

• Flowing, nonisothermal mechanisms– Rate-controlling steps include surface reaction, liquid-phase

diffusion through boundary layer, and solid state diffusion

J=k (C0-C)

Mass Change

x

T

max

T

min

0

A

s

A

p

A

p

balance points

(+)

(-)

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Eventually, Compatibility Issues Need To be Examined Under Dynamic, T Conditions

Ji = k(Csol,i – Ci)

Constant driving force for dissolution

Positive results from isothermal capsule experiments may not be reproduced under these conditions

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Current knowledge of candidate materials for DCLL system is largely limited to static capsule tests

• Substantial experimental database on ferritic steel compatibility with flowing Pb-Li– Comprehensive analysis of existing data is needed

• Database for other materials generally does not include information for nonisothermal flowing systems and effects of magnetic fields

• Very little is known about potential stress corrosion cracking mechanisms

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Concluding remarks

• Need to establish reference design (materials, operating conditions) asap

• Near-term compatibility R&D activities would focus on analysis of existing compatibility for ferritic/martensitic steel with flowing Pb-Li– Also continue limited number of static capsule tests on candidate

piping materials (possibility to avoid coatings or ceramic inserts)

• Medium-term activities would be centered on flowing loop experiments– Thermal convection loop– Other loops?

• Scoping experiments on stress-corrosion cracking should also be initiated in the near- to medium-term

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Chemical Analyses of the Pb-Li Revealed Little Reaction With SiC after 1000h

Li(at.%)

Si(ppma)

C(ppma)

O (ppma)N

(ppma)

Start n.d. <40 <170 1270 <40

800˚C

1000h17.5% <30 1850 4090 100

1100°C

1000h16.3% <30 1160 3550 90

1100˚C

2000h16.0% 185 1025 7890 200

No significant mass gains after any capsule test Si detected after 2,000h at 1100°C, still less than Kleykamp PbLi not analyzed yet for 5,000h 800°C or 1,000h 1200°C

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Specialized Capsule Experiments Have Been Used For SiC Exposures In Pb-17Li

800 and 1000˚C, 1000 h

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Negligible Change In Specimen Mass Before Or After Cleaning Was Observed

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Corrosion-Resistant Metallic Coatings for Pb-17Li

• At highest temperatures at and near first wall, SiC flow channel inserts can provide protection

• Ducting behind this more likely to be made of conventional steels

• Pb-17Li is quite corrosive toward certain ferrous and Ni-based alloys at temperatures above 450°C

• One possible solution to ducting protection is corrosion-resistant aluminized coatings on strong conventional alloys: aluminide surface layers should be stable in Pb-17Li (Hubberstey et al., Glasbrenner et al.)

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Al-Containing (Al2O3-forming) Alloys Showed Significantly Reduced Mass Losses In Pb-17Li

Specimen CapsuleMass Change

(mg/cm2)

316 SS 316 SS -0.7

316 SS Fe -5.7

316 SS Mo -3.8

ODS FeCrAl Mo -0.2

Fe-28Al-2Cr+Zr Mo -0.2

Ni-42.5Al Mo -0.1

Capsule test: 1000 h, 700˚C, Pb-17Li

0.25 m

*no preoxidation of specimens

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316 SS Results Can Be Understood Based On Fundamental Dissolution Driving Force

• Dissolution continues until saturation is reached

• For specimens of 316 SS, saturation is reached sooner in a 316 SS capsule because both are contributing solute (mainly Ni)

• Fe or Mo capsules are relatively inert

Ji = k(Csol,i – Ci)

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Surface Morphology Of Exposed Stainless SteelWas Consistent With Dissolution

1 m

316SS in Mo Capsule, 1000 h, 700˚C, Pb-17Li

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Examination Of Cross Sections ConfirmedSome Dissolution Had Occurred in Stainless Steel

10 m

2 m

1000 h, 700˚C, Pb-17Li

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Nickel Depletion Was Observed in Stainless SteelC

ou

nts

Energy, ev

Ni

Co

un

ts

Energy, ev

10 m

1000 h, 700˚C, Pb-17Li

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Aluminide-Formers Showed Little Mass Loss And Tended To From Stable, Protective Al-Rich Layers

2 m

1000 h, 700˚C, Pb-17Li

ODS-FeCrAlin Mo Capsule

Ni-42.5Alin Mo Capsule

2 m

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Fe

Energy, ev

Qualitative Analysis Indicated These Surface Layer Were Rich in Al and O (Likely Al2O3)

Al

OCo

un

ts

Energy, ev

1000 h, 700˚C, Pb-17LiODS-FeCrAl in Mo Capsule

Surface Layer

Subsurface Alloy

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Example Cycle Efficiency as a Function of Interface FS/Pb-17Li Temperature

0.36

0.37

0.38

0.39

0.4

0.41

0.42

0.43

0.44

0.45

475 490 510 530 550

Max. Interface FS/LiPb Temperature, o

C

Cycle Efficiency

For a fixed maximum neutron wall loading ~4.7 MW/m2,

-the max. η~38.8%, Tmax,FS<<550oC for an interface FS/LiPb temperature of 475 oC;

-the max. η~41.5%, Tmax,FS<<563oC for an interface FS/LiPb temperature of 510 oC.

TLiPb,out=700oC;Tmax,FW=800 oC

Tave,FW=700 oC; Ppump/Pthermal << 0.05

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