Task 2: Evaluation of the Causes &Mechanisms of IASCC in PWRs -Preliminary Results of IASCC Studyon BOR-60 Materials

Work sponsored by the US Nuclear Regulatory Commission

September 25-26, 2007

Nuclear Engineering Division

Argonne National Laboratory, Argonne, IL 60439

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

Experimental Effort: Loren Knoblich and Ed Listwan

2Work sponsored by theUS Nuclear Regulatory Commission

Objective and Approach

! Objective of the task:

– To improve the mechanistic understanding of IASCC in PWRs

• Effect of fluence (dose)

• Effect of alloying elements

• Effect of grain boundary structure

• Effect of cold-work

• Effect of irradiation conditions

! Experimental approach:

– Conduct SSRT tests and crack growth tests in PWR environment (to start)

– TEM examination on specimens relevant to PWRs (in progress)

! A critical issue:

– Influence of different irradiation conditions (flux & temp) on IASCC behavior

! Approach:

– Compare SSRT results on common materials irradiated to a comparable

dose level in both the Halden and BOR-60 reactors.

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Experimental

Due to the small dimension of the BOR-60 specimens, a special sample

grip and smaller pull rods are required for the BOR-60 SSRT tests.

! The same facility (test rig and recirculation loop) for the Halden

SSRT tests were used for testing the BOR-60 specimens.

! The BOR-60 specimens are smaller.

Halden

BOR-60

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Selected Common Alloys in the Halden & BOR-60 Irradiations

B<0.00121.000.0330.0060.470.0280.1130.909.66L5304-like alloy

B< 0.00118.550.0830.0161.810.0040.0190.468.91C3304L SA

O 0.008, Mo 0.0219.71<0.0010.0061.120.0020.0010.019.541327HP 304L SA

O 0.047, Mo <0.00519.210.0030.0051.110.005<0.0050.039.03945HP 304L SA

B <0.00118.430.0700.0601.000.0020.0180.478.23C12304 SA

B <0.00118.480.0650.0621.720.0130.0130.398.75C9304 SA

B 0.00118.110.0600.0601.000.0020.0380.508.12C1304 SA

Other ElementsCrNCMnSPSiNi

Composition (wt.%)Heat

ID

Material

Type

7.4 x 10-7 s-14.8 dpaSodium~ 320ºCBOR-60

3.3 x 10-7 s-13 dpaHe~ 290ºCHalden

SSRT strain rateDoseIrr. Env.Irr. Temp.Reactor

! Composition

! Differences between the two irradiations

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SSRT Tests in High-DO Water (1)

IG cracking is severe in the high-S

Type 304 SS, but no IG fracture in the

low-S Type 304 SS.

Low-S

Low-S

High-S

0

200

400

600

800

1000

0 2 4 6 8 10 12 14

Str

ess (

MP

a)

Strain (%)

Type 304 SSs, SA

Irr. Temp ~320oC

Dose = 4.8 dpa

Strain rate = 7.4x10-7

s-1

a

C9

C1

C12

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SSRT Tests in High-DO Water (2)

Low-C Type 304 SS irradiated in the BOR-60 does not show IG crack.

304-like alloy

with low C

but high S

and P.

Low-C Type

304 SS

0

200

400

600

800

1000

0 2 4 6 8 10 12 14

Str

ess (

MP

a)

Strain (%)

Type 304L SSs, SA

Irr. Temp ~320oC

Dose = 4.8 dpa

Strain rate = 7.4x10-7

s-1

b

C3

L5

7Work sponsored by theUS Nuclear Regulatory Commission

SSRT Tests in High-DO Water (3)

IG cracking readily develops in

high-O Type 304L SS.

Low-O Type 304L SS

High-O Type

304L SS

0

200

400

600

800

1000

0 2 4 6 8 10 12 14

Str

ess (

MP

a)

Strain (%)

Type 304L SSs, SA

Irr. Temp ~320oC

Dose = 4.8 dpa

Strain rate = 7.4x10-7

s-1

c

327

945

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Irradiation Hardening

Yield strength of SA SSs saturates between 3 & 5 dpa.

0

200

400

600

800

1000

0 5 10 15 20

This work

Chung et al. [20]

Chen et al. [19]

Alexander et al. [21]

Mills et al. [22]

Sindelar et al. [23]

YS

(M

Pa

)

Dose (dpa)

Irr. Temp: 90 ~ 427 oC

Test Temp: RT ~ 427 oC

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Comparison of Irradiation Hardening Resulting from theHalden & BOR-60 Irradiations

Both the YS and UTS are higher for Halden specimens although

dose is slightly lower (3 vs. 4.8 dpa).

600

700

800

900

1000

600 700 800 900 1000

YS

of H

ald

en s

pecim

ens (

MP

a)

YS of BOR-60 specimens (MPa)

(a)

~ 50 MPa

600

700

800

900

1000

600 700 800 900 1000U

TS

of H

ald

en s

pecim

ens (

MP

a)

UTS of BOR-60 specimens (MPa)

(b)

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Comparison of Ductility between Halden & BOR-60 Specimens

Elongation of BOR-60 specimens more than that of Halden specimens.

0

5

10

15

0 5 10 15

UE

of

Ha

lden s

pe

cim

ens (

%)

UE of BOR-60 specimens (%)

Estimated

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Comparison of IG Cracking in the Halden & BOR-60 Specimens

! IG cracking is more severe for the BOR-60 specimens with high-O content.

! More heats from Halden irradiations showed IG cracking.

BOR-60 irradiation appears somewhat less damaging than Halden conditions.

Type 304 SS

0

20

40

60

80

100

BOR-60

Halden

C1 C9 C12 C3 L5 327 945

IG a

rea fra

ction (

%)

Type 304L SS HP 304L SS

C1

C9

C12

C3

L5 327

945

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Possible Explanation for the Dissimilar Effects Resultingfrom the Halden & BOR-60 Irradiations

! Irradiation effects (such as IASCC) are caused by surviving point defects

rather than the point defects resulting from the cascade damage.

– The defect survival rate for a low energy cascade from thermal neutron

(Halden) is higher than that caused by fast neutron (BOR-60).

– A higher flux in the BOR-60 irradiation with respect to the Halden irradiation

may lead to a lower survival rate.

– The defect survival rate is lower at a higher irradiation temperature (TBOR-60 >

THalden). Microstructure evolution is very sensitive at around 300ºC for SSs.

! Radiation damage ! Microstructure evolution – rate theory

Seeger, A., 1958

( )

( )

v v v

v v v v v i v v

i i i

i i i i v i i i

D C CD C U G RC C K C

kT t

DC CD C U G RC C K C

kT t

!" " + " + # # =

!

!" " + " + # # =

!

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Conclusions

! The SSRT in high-DO water produced similar results among the

different materials irradiated in both Halden & BOR-60 reactors.

! The post-irradiation strengths (YS and UTS) for the BOR-60

specimens were consistently lower than those of the corresponding

Halden specimens. The BOR-60 specimens also elongated more

than their Halden counterparts.

! The IG cracking resulting from high-DO water tests for most of the

materials was consistent in both the Halden & BOR-60 irradiation.

Nonetheless, for the materials that were investigated, BOR-60

irradiation appears somewhat less damaging than Halden irradiation.

! Based on present results it is not clear whether BOR-60 is prototypical

of PWRs; however they demonstrate that it is not for BWRs