Work sponsored by the US Nuclear Regulatory Commission

Task 1: Evaluation of the Causes &Mechanisms of IASCC in BWRs -IASCC Susceptibility of Austenitic SSs& Alloy 690

September 25-26, 2007

Nuclear Engineering Division

Argonne National Laboratory, Argonne, IL 60439

Investigators: Yiren Chen, Omesh Chopra, Bill Shack, Bill Soppet,

and Nancy Dietz Rago1

Experimental Effort: Loren Knoblich and Ed Listwan

1Chemical Engineering Division

2Work sponsored by theUS Nuclear Regulatory Commission

Objectives and Approach

Objectives:

– Evaluate the influence of GBE treatment;

– Evaluate the influence of alloy composition;

– Evaluate the effect of irradiation dose.

Approach:

SSRT tests in high-DO water at 289ºC, complemented with

Fractography on:

– specimens with different proportions of special boundaries

– specimens with various chemical compositions

– specimens irradiated to a range of doses.

3Work sponsored by theUS Nuclear Regulatory Commission

Alloys

Fe 10.26, Al 0.22, Ti 0.2929.10-0.0100.420.0030.0260.4259.40GBE Alloy 690GBE690

Fe 9.02, Co 0.007, Cu 0.0129.24-0.0300.150.001-0.0561.49Alloy 690690

Mo 2.39, Ti 0.027, Cu 0.2117.250.0640.0120.920.0020.0070.7212.30Type 316LN SS, Ti-doped625

Mo 2.38, Cu 0.2117.230.1030.0190.970.0020.0070.712.20Type 316LN SS623

Mo 2.07, Cu 0.37, Co 0.0916.340.0500.0411.590.0250.0290.3511.16GBE Type 316 SSGBE316

Mo <0.005, O 0.04719.210.0030.0051.110.005<0.0050.039.03High-purity Type 304L SS

with high O945

Mo 0.02, O 0.00819.71<0.0010.0061.120.0020.0010.019.54High-purity Type 304L SS

with low O327

Mo 0.37, Cu 0.3518.350.0900.0201.740.0070.0280.458.33GBE Type 304L SSGBE304L

Mo 0.37, Co 0.13, Cu 0.3518.350.0900.0231.740.0070.0280.458.33Type 304L SS.304L

Mo 0.23, Co 0.10, Cu 0.3118.280.0520.0541.730.0060.0290.418.19GBE Type 304 SSGBE304

Mo 0.3718.540.0680.041.380.0190.0270.688.45Type 304 SS from ABBa333

OthersCrNCMnSPSiNi

Composition (wt.%)

DescriptionHeat ID

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! Flat dog-bone specimen

! Dry irradiation in He-sealed capsules in Halden boiling heavy water reactor

– Dose: 0.45, 1.34 and 3 dpa (phase-I); 1.96 and 2.44 dpa (phase-II)

– Irradiation temperature (phase-II): ~290-305°C

– Radioactivity: ~ 200 R/hr on contact, 0.3 Ci.

SSRT specimens and Irradiation condition

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SSRT test condition

1

5

6

v6 v7

v8

v10

9

8

32

14 15

16

17 18

19

20

21

22

23

25 26

28 31

V11

V12

V13

V17

11

24

34

2 v1

3 v2

v3

4 v5 v4

7

10

13

27

29

30

12 33

35

36

v9

V14

V15V16

V18

Low pressure High pressure

In Cell

29B

v1937

38

Temperature - 289°C DO - 8 ppm

Pressure - 9.31 MPa (1350 psig) Conductivity - 0.06~0.1 µS/cm

pH - 6.4 ~ 7.2 ECP – 150~200 mV (ss)

Flow rate – 15~30 ml /min 270~310 mV (Pt)

Strain rate ~ 3.31x10-7 s-1

Stabilize test condition by soaking the specimen in high-DO water >24 hr

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Influence of irradiation and high-DO water on SSRT curve

- The yield strength for irradiated material is similar in air and in water.

- The reduction in ductility is attributed to both neutron irradiation and

high-DO water environment.

Strain rate:

~ 3.31x10-7 s-1

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35 40

Str

ess (

MP

a)

Strain (%)

GBE Type 304L SS

non-irr., in water

1.96 dpa, in water

1.96 dpa, in air

in air test - 287 ~292 oC

in water test - 289 oC

Pressure ~ 9.3 MPa pH ~ 6.8 DO ~ 8 ppm

Conductivity ~ 0.067 µSv/cm

Flow ~ 20 ml/min

Strain rate:

8.15 x 10 -7

s-1

Strain rate:

3.31 x 10 -7

s-1

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SSRT tests in high-DO water environment

0

200

400

600

800

1000

0 2 4 6 8 10

Str

ess (

MP

a)

Strain (%)

GBE304 (1.96 dpa)

Strain rate = 3.31 x 10-7

s-1

Type 304 SS

333 (2.44 dpa)

(a)

0

200

400

600

800

1000

0 2 4 6 8 10

Str

ess (

MP

a)

Strain (%)

GBE304L (1.96 dpa)

Strain rate = 3.31 x 10-7

s-1

304L (1.96 dpa)

Type 304L SS

327 (2.44 dpa)

945 (2.44 dpa)

(b)

0

200

400

600

800

1000

0 2 4 6 8 10

Str

ess (

MP

a)

Strain (%)

GBE316 (1.96 dpa)

Strain rate = 3.31 x 10-7

s-1

623 (2.44 dpa)

Type 316 and 316L SSs

625 (2.44 dpa)

(c)

0

200

400

600

800

1000

0 5 10 15 20 25 30

Str

ess (

MP

a)

Strain (%)

690 (1.96 dpa)

Strain rate = 3.31 x 10-7

s-1

Alloy 690

GBE690 (1.96 dpa)

(d)

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Dose dependence of yield strength and ultimate tensile strength

Rate of increase of yield strength

decreases significantly at 3 dpa.

0

500

1000

1500

0 0.5 1 1.5 2 2.5 3 3.5

Yie

ld S

tre

ng

th (

MP

a)

Dose (dpa)

0

500

1000

1500

0 0.5 1 1.5 2 2.5 3 3.5

Ultim

ate

Te

nsile

Str

en

gth

(M

Pa

)

Dose (dpa)

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Dose dependence of uniform elongation and total elongation

Loss of elongation reaches

minimum at less than 2 dpa

in high-DO water.

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3 3.5

Un

ifo

rm E

lon

ga

tio

n (

%)

Dose (dpa)

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3 3.5

Tota

l E

longation (

%)

Dose (dpa)

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Correlation between C content and UE of SSRT tests

No other correlation found between other elements & SSRT elongation

0

1

2

3

4

5

6

7

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Type 304 SS, with GBE

Type 304 SS, w/o GBE

Type 316 SS, with GBE

Type 316 SS, w/o GBE

Uniform

Elo

ngation (

%)

Carbon Content (wt.%)

11Work sponsored by theUS Nuclear Regulatory Commission

~ 2 mm

0

.

7

m

m

3.15 mm

Fractographic analyses

! Cut fracture tip to reduce radioactivity: <100 mR/hr @ 30 cm; <7mCi.

! Clean off loose contamination: < 200 dpm

! Hitachi S-3000N SEM, secondary electron image at 30-kV acceleration

voltage with a 25-mm work distance.

TG

Ductile fracture

IG

IG

d1

TGl1

l2

d2

! Characterize fracture surface

– IG or TG area fractions

– Number of IG or TG cracks

…

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Type 304L SS with high O content (Heat 945)

Dose = 2.44 dpa

YS = 666 MPa

UTS = 666 MPa

UE = 1.22%

TE = 2.20%

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Susceptibility to cracking – IG and TG area fractions

- Type 304 and 304L SSs are more vulnerable to IG cracking in high-DO water;

- Large TG cracking was observed in GBE Type 316;

- High-O content stimulates IG cracking in HP Type 304L SS;

- Low-C Type 304 SSs show more IG cracking.

0

10

20

30

40

50

IG %

TG %

Are

a F

ractio

n (

%)

333

GBE304

304L

GBE304L

327

945

GBE316

623

625

690

GBE690

Type 304 Type 304L Type 316 Alloy 690

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Likelihood of IG crack initiation

-The highest IG initiation is found in Type 304L SS with high-O content.

- No IG initiation in high-purity Type 316 SSs, and GBE 690.

0

1

2

3

4

Num

ber

of IG

Cra

cks / u

niform

elo

ngation

333

GBE304

304L

GBE304L

327

945

GBE316

623 625690

GBE690

Type 304 Type 304L Type 316 Alloy 690

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Effect of GBE! Treatment

! GBE treatment does not appear to improve IG cracking in Type 304 and 304L SSs

! The effectiveness of GBE treatment is inconclusive for Type 316 SS (no base tested)

! GBE treatment appears to suppress IG cracking in Alloy 690 at !2 dpa

! GBE CSL (""29) fractions:

–67% Type 304 SS;

–66% Type 304L SS;

–66% Type 316 SS;

–71% Alloy 690.

0

5

10

15

20

25

30

35

nonGBE

GBE

IG A

rea

Fra

ctio

n (

%)

333

GBE304

304L

GBE304L

GBE316

690

GBE690

Type 304 Type 304L Type 316 Alloy 690

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Effect of Alloying Elements

! Type 304 SSs cracked more

than Type 316 SSs (Mo

addition is helpful to reduce

cracking)

! Type 304L SS cracked more

than Type 304 SS (blue vs.

orange)

! Low-O Type 304 SS cracked

less (light blue vs. dark blue)

Appear to be significant differences within alloy types; such heat-to-heat variability

may be dependent on differences in microstructure & minor impurity levels

0

5

10

15

20

25

30

35

Type 304 SS

Type 304L SS

Low-O Type 304L SS

Type 316 SS

IG A

rea fra

ction (

%)

333

GBE304

304L

GBE304L

327

945

GBE316

623 625

Type 304 Type 316

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Effect of Irradiation-Dose Threshold

IG cracking does not occur below 0.45 dpa (3 x 1020 n/cm2) for the

commercial heats of austenitic SSs in the Halden irradiations.

Halden-I data

is included.

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

333

GBE304

304L

GBE304L

327

945

GBE316

623

625

690

GBE690

C1

C3

C9

C10

C12

C16

C19

C21

IG a

rea

fra

ctio

n (

%)

Dose (dpa)

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Conclusions

! GBE process used in this study shows no beneficial effect for Types 304 or

304L SS. However, the GBE treatment results in a smaller reduction in UE

for Alloy 690 at 2 dpa, & reduces its IASCC susceptibility in high-DO water.

! Type 316 SSs are generally more resistant to IG cracking than Type 304 SSs.

The presence of Mo or the higher Ni concentrations in Type 316 SSs may be

responsible.

! The O content of the material is critical for IASCC susceptibility; high O

content contributes to IASCC susceptibility by enhancing IG crack initiation.

! The UE obtained from SSRT tests in high-DO water increases linearly with C

content below 0.06 wt.%. Also, the low-C SSs are more susceptible to

IGSCC (results consistent with data from Halden-I irradiations).