P2-148

September 28 Tuesday

Flow Accelerated Corrosion and

Erosion-Corrosion of RAFM Steel

in Liquid Breeders

Masatoshi Kondoa, Takeo Murogaa, Akio Sagaraa, Tsisar Valentynb,

Akihiro Suzukic, Takayuki Teraic, Minoru Takahashid,

Naoki Fujiie, Yukihiro Yokoyamaf, Hiroshi Miyamotof, Eiji Nakamuraf

a. National Institute for Fusion Science, Toki, Japan.

b. Physico-Mechanical Institute of National Academy of Sciences of

Ukraine, Ukraine

c. University of Tokyo, Tokyo, Japan.

d. Tokyo Institute of Technology, Tokyo, Japan.

e. Biko chemical company, kobe, 658-0013, Japan

f. Santoku cooperation, kobe, 673-0443, Japan1

1. Background and purpose

2. Experimental condition

2.1 Experimental apparatus

2.2 Test conditions

3. Results and discussion

4. Conclusions

Contents of my presentation

2

Compatibility of liquid breeders, i.e. lithium (Li), lithium-lead

(Pb-17Li), 46.5LiF-11.5NaF-42KF (Flinak) and 66LiF-34BeF2

(Flibe), with structural materials is one of the critical issues

for the development of fusion blanket systems.

1.Background and purpose

FFHR molten salt /RAFM blanket

designed by

A. Sagara et al.,

Fusion Engineering and Design 81

(2006) 2703-2712 3

KOREAN lithium/RAFM blanket

Y. Kim et al. /

Fusion Engineering and Design 75–79

(2005) 1067–1070

Compatibility of steels in fluids

The corrosion rate must be higher at higher flow rate of these fluids,

and the phenomenon was called a flow accelerated corrosion (FAC). An

erosion of a corroded surface by the shear stress of the flow called an

erosion-corrosion is also an important phenomenon. However, these

characteristics in liquid metals and molten salts are limited so far.

Erosion occurrence in liquid metal Pb-Bi was reported in the previous

studies.

Specimen of

STBA26(9Cr-1Mo) steelSpecimen

holder

Pb-Bi flow

250µm

Cross section of eroded part

Erosion – corrosion in lead-bismuth eutectic

steel

Erosion

M. Kondo, M. Takahashi et al, J. Nucl. Mater., 343, 349-359 (2005).

steel

Erosion-

corrosion

5

Corrosion data in liquid Li, Pb-Li and molten salt was not able to be

directly compared with each other because of the different corrosion

apparatus and conditions.

(For example, comparison of weight loss data between different

corrosion systems and apparatus is not easy)

Therefore, The tests were performed at the same conditions, and the

compatibility with the fluids was compared with each other. Overall

mass transfer coefficient is proposed to evaluate the corrosion ratio

in the present study.

The purpose of the present study is to investigate the compatibility of

reduced activation ferritic/martensitic (RAFM) steel, JLF-1, in the liquid

breeders in static and flowing condition. The characteristics of the

flow accelerated corrosion and the erosion-corrosion in the fluids

were discussed.

Purpose

6

2. Experimental conditions2.1 Experimental apparatus

Heater

Thermo couple

Impeller(Mo)

Magnet

coupling

Motor for rotate

impeller

Specimens

Li

Pot (316)

Crucible

(9Crsteel)

Specimen

holder (410)

33mm48mm

16m

m3

6m

m

Li

Thermo couple

Specimens

Heater

Heat

insulation

Specimen holder

(12Cr steel )Pot

(Made of 316)

Crucible

(9Cr steel)

Specimens

Cover

gas: Ar

I.D.

48mm

Ar

Static test apparatus

Volume 92cc

Temp. 500-700

Stirring test apparatus

Li volume 65cc

Temp. 500-600

Rotating speed max 100rpm

Corresponds to 0.17m/s

2

Rend

mixing

dnv

7

2. Experimental conditions

2.2 Test condition

Test

IDStatic or

Stirred

Temp.

(ºC)

Exposure time

(hours) [Ref.]

Material of

crucible

V/ Stotal (m) Re

number

for mixing

Li

A

Static 600

100 Mo 0.11 -

B 250[8], 750[8] Mo 3.3x10-2 -

C 250[9], 750 12Cr steel 1.0 x10-2 -

D Flowing 600 250[10] 12Cr steel 9.8x10-3 2859

Pb-17LiE Static 600 750, 3000 JLF-1 2.6x10-3 -

F Flowing 600 250 12Cr steel 9.8x10-3 18512

Flinak

GStatic 600

200[7],1000[7],

2200JLF-1 steel

2.6x10-3 -

H Flowing 600 250[7], 2200 SUS316L* 9.8x10-3 949

8

92cc

65cc 3cc

Specimen

Test E, GTest A, B Test C Test D, F, HSpecimen

Impeller

Non-corrosion surface area

Corrosion surface area

(Specimen, crucible surface)

Fe Cr W Non metal

Li 0.85 0.12 0.31 Nitrogen: 65

Pb-17Li 2.2 0.17 0.52 -

Flinak 52 2.6 - H2O: 42.6

Initial impurity of liquid breeders Schematic image of test assemble

Results and discussion (Li)

9BCT

a a

c

a a

a

BCC

C Fe

600ºC 250h

-Corrosion at static condition

-Depletion of carbide and carbon from steel

-Cr depletion

-Phase transformation from martensite to

ferrite due to carbon depletion

-Coalescence of subgrains

Diffusion of Li to grain boundary

decreased grain bonding

Erosion-corrosion

stirring test at 600 ?C5µm

Rough surface

5µm

Subgrain

5 micro

5 micro

Not able to be coalesced

600ºC 250h

Static Flowing

Results and discussion (Pb-17Li)

5µm

Flowing condition(250hours)Static condition (3000hours)

5µm

ICP-MS analysis for Pb-Li used for static test (unit : wppm)

Fe Cr W Ni Mo

Pb-17Li (Initial) 2.2 0.17 0.52 1.3 0.052

After 250- hour test (Static) 0.85 3.6 3.4 - -

After 3000-hour test (Static) 10 4.5 3.9 - -

Cr dissolution → Cr saturation (Cr solubility is low)

Fe dissolution → Fe has large solubility in Pb-17Li 10

Erosion- corrosion

Penetration to

boundary

Flow accelerated

corrosion

Liquid

breeders

Erosion corrosion

Peeled off of

subgrains by flow

Subgrains

PAG

Packet

boundary

Block

boundary

Lath

boundary

Li dissolves the carbide, and attacked the packet, block, lath and/or subgrain

boundaries where had the carbide precipitated. From these facts, the

mechanism of erosion-corrosion of JLF-1 steel in flowing Li was summarized

in Figure. By the flowing test in Pb-Li, the similar morphology was obtained

and this indicated the occurrence of the erosion-corrosion. In the Flinak, the

erosion-corrosion was not detected possibly because the sensitivity of the

boundaries for the Flinak was not strong due to the chemical stability. 15

Results and discussion (Flinak)

250hrs 250hrs

Pitting

corrosionAttack for

boundary* Small pit

5µm

250 hrs (Test H)

The corrosion of JLF-1 was small in

purified Flinak at flowing condition

induced by impeller in pot. The phase

transformation on the surface was

observed. The number of the pitting

corrosion on the surface was less

than that at static condition, because

the impeller induced flow removed the

local difference of impurity

concentration on the surface in Flinak.

The weight loss of the specimens was

lower than that at static condition.

10µm

11

October 12 16:30-18:30

ISFNT-9Masatoshi KONDO

E-mail: kondo.masatoshi@nifs.ac.jp

3. Results and Discussion (3.2 Corrosion in purified Flinak)

5µm

Pitting

Phase transformed zone

(C depleted zone)

Normal part

5µm

Cr depleted zone

Cr enriched zone

Phase transformed zone

Grain boundary

Fe

Cr W

Fe

Cr W

200 hrs(P-C-1) 1000hrs (P-C-2)

1000hrs200hrs

10µm 10µm

The weight loss was

much less than that in

non-purified Flinak.

The pitting corrosion

was partially observed

on the surface.

The corrosion in

purified Flinak at

static condition

was the local

corrosion for the

grain boundary,

though the

intensity was

lower than that

in non-purified

Flinak.

Steel

Pitting corrosion in Flinak

Grain

boundary

Anode

Flinak

Cathode

Electrical circuitFe2+

Weight loss

Li Pb-17Li

FlinakAfter the tests in Li, specimens were rinsed in

water at room temperature. The specimen tested in

Pb-17Li was rinsed in Li at 350 ºC for 3 hours to

remove Pb-17Li from the specimen due to the

dissolution of Pb-17Li into Li. The adhered Li on

specimen was then removed by water. The

specimen tested in Flinak was rinsed in LiCl-KCl at

500 ºC, and the adhered LiCl-KCl was rinsed in

water. All the specimens were finally rinsed in

acetone to remove water. The weight change of the

specimens by the exposure to the liquid breeders

was measured using an electro reading balance

with accuracy of 0.1mg.

Solid line and dotted one by modeling calculation shown in next page

Erosion-corrosion

12

Li (65wppm nitrogen) Pb-17Li PbFlinak

(42.5wppm H2O)

Cs wppm<molppm>

Fe - * 47 (600ºC) ~<145> 34 (600ºC) <126> 50 (600ºC)

Cr52.4 (800 ºC) <7>~

94.3 (600ºC) <12.6>**10 (500ºC) <40> 1 (600ºC) <3.7 > 50 (600ºC)

D (m2/s)Fe 4 x10-8 (600ºC) 4 ±2 x10-14 (500ºC) 1.2x 10-9(600ºC) 5.4x10-8

Cr 2.1x10-8 (570 ºC) 8 ±2.5 x10-11 (500ºC) - 2x10-9***

Solubility and diffusion coefficient

Nomenclature

C: concentration of metal element in fluids [wppm]

Cs: Solubility of element in fluids [wppm]

D: diffusion coefficient [m2/s]

d: Width of impeller [m]

e: Thickness of boundary layer for concentration [m]

J: Overall mass transfer ratio [g/m2s]

h: Overall mass transfer coefficient [m/s]

hm, e : Overall mass transfer coefficient at flowing

condition in experiment

hm, t : Overall mass transfer coefficient at flowing

condition in theory [m/s]

n: Rotatig speed [s-1]

Ss: Surface area of specimens [m2]

Sc: Surface area of crucible [m2]

t: Test time [s]

ρ: Density of liquid breeders [g/m3]

μ: Viscosity of liquid breeders [mPa•s]

ν: Kinetic viscosity of liquid breeders [m2/s]

V: Volume of liquid breeders [m3]

v: Averaged velocity of liquid breeder [m/s]

Δm: Wight loss of specimen in total [g/m2]

Ω: Constant for mass transfer in mixing flow D

νSc 0.7f0.644D0.344ν0.45.67de

C)-(CshJdt

dC

ScSs

Vρ

)C(Cse

D)Cs-C)(hJ

mt

1/3(Sc)2/3)mixing

(ReD

dhSh mt

))V

Sc)th(Ssexp(Cs(1C

))V

hStexp(ρVCs(1Δm

13

Mass

transfer of

element in

flow

FAC modeling based on mass transfer

Li (65wppm nitrogen) Pb-17Li Flinak

(42.5wppm H2O)

h static experimental (m/s) 2.8x10-8 1.2x10-9 -

h flow experimental (m/s) (erosion-corrosion) 4.2x10-9 1.2x10-8

h flow theory (m/s) 9.9x10-5 - 1.3x10-4 2.1x10-8 - 1.4x10-7 2.2x10-5 - 3.5x10-4

Modeling (Overall mass transfer coefficient)

Discussion on release rate in corrosion process

14

Overall mass transfer coefficient

obtained from experiment ( hm,e)

Overall mass transfer coefficient

obtained from hydrodynamic non

dimension number

Flow Flow

No binding

of element

on specimen

surface

Binding of

element on

specimen

surface

Release rate

( hm,t)

Erosion- corrosion

Penetration to

boundary

Flow accelerated

corrosion

Liquid

breeders

Erosion corrosion

Peeled off of

subgrains by flow

Subgrains

PAG

Packet

boundary

Block

boundary

Lath

boundary

Li dissolves the carbide, and attacked the packet, block, lath and/or subgrain

boundaries where had the carbide precipitated. From these facts, the

mechanism of erosion-corrosion of JLF-1 steel in flowing Li was summarized

in Figure. By the flowing test in Pb-Li, the similar morphology was obtained

and this indicated the occurrence of the erosion-corrosion. In the Flinak, the

erosion-corrosion was not detected possibly because the sensitivity of the

boundaries for the Flinak was not strong due to the chemical stability. 15

Conclusion

Corrosion experiments for RAFM, JLF-1 steel (Fe-9Cr-2w-0.1C) in 3types

of flowing liquid breeders (i.e. Li, Pb-17Li and Flinak) were performed at

the same conditions. The compatibility of the fluids for the steel was

compared with each other. Major conclusions are as follows;

(1) The weight loss of specimens in liquid breeders was evaluated by a

corrosion model based on mass transfer. It was found that the model can

be applied for the different test system with different quantity of liquid

breeders and different surface area of the systems.

(2) The overall mass transfer ratio in Li at static condition was larger than

that of Pb-Li, though the solubility of the metal element of the steel in Pb-

17Li was higher than that of Li. The flow enhanced the dissolution of

element of the steel in liquid metals. In the Flinak, the effect of the flow was

negligible.

(3) An erosion- corrosion of JLF-1 in Li and Pb-Li was caused by the

peeling off of the subgrain on the corroded surface by the flow.16

October 12 16:30-18:30

ISFNT-9Masatoshi KONDO

E-mail: kondo.masatoshi@nifs.ac.jp

Back up Results and Discussion (3.1 Corrosion in non-purified Flinak with H2O)

5µm5µm

Normal partCr rich inner

oxide layerFe rich

outer oxide

layer

Outer layer was damaged

10µm

230 hrs (N-C-1)230 hrs (N-C-2) 1000hrs (N-C-3) [4]

Fe

Cr W

Surface state is similar

Outer layer

Inner layer Inner layer

Dissolution of oxide into Flinak

and peeled of oxide layer

Oxide layer

formation

Steel Steel Steel Steel

O H O

Oxidation corrosion in Flinak

Cr rich inner layer

formationFe rich layer

Cr rich surface

5µm

10µm

230 hrs1000 hrs

Cr depleted zone

10µm

The local corrosion

at grain boundary

and lath boundary

was detected. Fe was

selectively dissolved

from the JLF-1

surface into Flinak.

The formed oxide

layer in non-purified

Flinak had double

layer structure as

outer Fe-rich oxide

layer and inner Cr –rich oxide layer. The

oxide layer was

damaged, and non-

protection for the

corrosion was

indicated.

M.P.

(K)

Thermal conductivity

(W / (m x K))

Density

(kg/m3)

Viscosity

(mPas)

Li Alkali metal 453.7 53.7 (800K) 481 (800K) 0.344 (800K) Fusion blanket

Na Alkali metal 371 66.1 (800K) 826 (800K) 0.232 (800K) Coolant for FBR

Pb Heavy metal 600.7 15.4 (800K) 10360 (800K) 1.74 (800K) Coolant for FBR

Pb-17Li Heavy metal 508 9568 (800K) - Fusion blanket

Pb-Bi Heavy metal 397 14.9 (800K) 10087(800K) 1.33 (800K) Coolant for FBR

Flinak(LiF-NaF-KF)

Molten salt 727 1.2 2146 (800K) 4.1 (900K) Fusion blanket

Flibe(LiF-BeF2)

Molten salt 772 1.2 1993 (800K) 7.5 (800K) Fusion blanket

FlinakLiquid

LithiumLi+

Free

electron

High thermal conductivity in liquid metal High chemical stability of molten salt

Li+ F-+

Already stable

state by ion

bonding4