Irradiation Embrittlement Mechanical Properties and Irradiated Assisted Stress Corrosion Cracking

Dr. Appajosula S. Rao, Darrell Dunn U.S. Nuclear Regulatory Commission

Y. Chen, O. K. Chopra and W. J. Shack Nuclear Engineering Division

Argonne National Laboratory, Argonne, IL 60439

Outline

NRC Research ActivitiesSSRT TestingFracture Toughness TestingResultsSummaryFuture Work

2

NRC Research

NRC IASCC research focused on the following areasEvaluate effectiveness of SCC mitigations• Hydrogen Water Chemistry• Grain Boundary Engineering

Evaluate CGR models for BWRs and PWRsEvaluate the causes, mechanisms and effects of EAC on BWR internalsEffect of cold work on crack growth ratesReview and evaluation of EAC in vessel internal components and emerging aging degradation issuesRadiation embrittlement at relevant to PWR conditionsRadiation and thermal embrittlement of cast austenitic stainlesssteels

3

4

Alloys for SSRT

304-like alloy with high Ni and CrL5Low S, Type 304 SSC12

Effect of SHigh S, Type 304 SSC9Type 304L SSC3 (SA, CW)Low S, Type 304 SS, high PC1 (SA, CW)High-purity Type 304L SS with high O945

Effect of O High-purity Type 304L SS with low O327Type 316LN SS, Ti-doped625

Effect of Ti Type 316LN SS623GBE Alloy 690GBE690Alloy 690690GBE Type 316 SSGBE316

Effect of GBEGBE Type 304L SSGBE304LType 304L SS.304LGBE Type 304 SSGBE304Type 304 SS from ABB333

ObjectivesDescriptionHeat ID

}}

}

Common Materials in Halden & BOR-60Irr.

5

SSRT Specimens

Halden

BOR-60

Ratio(Halden / BOR-60)

Thickness (t) 1

Gauge cross-section (A) 2

Gauge length (l) 2.5

Elongations are expected to be different between the Halden and BOR-60 specimens (l/A0.5 ≈ 1.8)

6

Experimental – Irradiation

Halden reactor – a boiling heavy water reactorDry irradiation in He-sealed capsulesIrradiation temperature ~ 290°CDose rate ~ 10-7 dpa/sHe/dpa ratio for a Typical LWR: ~2-5 appm/dpa.

BOR-60 reactor – a sodium cooled fast breeder reactorSamples exposed to sodiumIrradiation temperature ~ 320°CDose rate ~ 9x10-7 dpa/sHe/dpa ratio for a Typical fast reactor: < 0.5 appm/dpa

7

SSRT Testing

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 v13 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 ppmPressure - 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: Halden ~ 3.3x10-7 s-1; BOR-60: ~ 7.4x10-7 s-1

Loading grip for BOR-60 specimen

8

~ 2 mm

0.7 mm 3.15 mm

Fractography – SSRT Specimens

TG

Ductile fracture

IG

IG

d1

TGl1

l2

d2

Characterize fracture surfaceIG or TG area fractionsNumber of IG or TG areas

~ 1.5 mm

~ 0.7

mm

Sectioned Halden specimen

BOR-60 specimen

Fracture Toughness Testing

Weldments304L submerge arc (SA) weld -- a double-V butt weld on Type 304L hot-rolled plates (ASME SA240 ) using ER308L filler rods.304 shield metal arc (SMA) weld -- a single-V butt weld on Type 304 plates using E308 filler rods.Post-weld thermal treatment -- 500°C for 24 hours (to simulate the effect of low-temperature sensitization).

Four materials304L SA HAZ, as-welded304L SA HAZ, thermally-treated304 SMA HAZ, as welded304 SMA HAZ, thermally-treated

9

Chemical composition of the weld HAZ materials

Weld Heat ID Ni Si P S Mn C N Cr Mo O

304 SMA 10285 8.45 0.60 0.015 0.007 1.90 0.070 0.084 18.56 0.51 0.013 304L SA GG Top Shell 9.05 0.53 0.027 0.016 1.84 0.013 0.064 18.23 0.44 0.010

Fracture Toughness Specimens

10

Specimen geometry – 1/4T-CT

304L SA weld 304 SMA weld

Fracture Toughness Specimens - Irradiation

11

Irradiation conditions for the weld HAZ compact tension specimens

Material Heat Treatment Fast Neutron Fluence

E >1 MeV (x1021 n/cm2)

Displacement Damage

(dpa)

Irradiation Temperature

(°C) 0.50 0.75 ~290 As-welded 1.44 2.15 290-296 GG 304L SA HAZ

24 h @ 500°C 1.63 2.43 ~290 0.50 0.75 ~290 As-welded 1.44 2.15 290-296 0.50 0.75 ~290

304 SS SMA HAZ 24 h @ 500°C

1.44 2.15 290-296

Irradiated in Halden reactor in helium-sealed capsules

Fracture Toughness Test Conditions

Temp: ≈290°CDO: ≈350 ppb with N2 + 1% O2 cover gas

<30 ppb with 4% H2 cover gasFlow rate: 15–25 mL/minConductivity: 0.08 - 0.12 μS/cmKmax: approximately constant by load sheddingK/size criterion: B and (W-a) ≥2.5*(K/σeff)2, where σeff = (σy + σu )/2 for

nonirradiated specimens, σeff = σy-irr for irradiated specimensJ-R curve tests: constant extension rate of 0.43 μm/s. Use a blunting line

given by Δa = J/(4σf).

12

13

Effect of Irradiation Dose on Yield Strength

Irradiation hardening and embitterment start to appear at dose <0.5 dpa.

0

200

400

600

800

1000

0 10 20 30 40 50

Stre

ss (M

Pa)

Strain (%)

12 dpa

non-irr.

Test temp. = 320oC

Strain rate = 7.4 x 10 -7 s-1

5 dpa

316 SS BOR-60 Irradiation

0

500

1000

1500

0 0.5 1 1.5 2 2.5 3 3.5

Yie

ld S

treng

th (M

Pa)

Dose (dpa)

NUREG\CR-6965

Effect of Irradiation Dose on Total Elongation

14

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3 3.5

Tota

l Elo

ngat

ion

(%)

Dose (dpa)

Irradiation hardening starts to saturate around 3-5 dpa, and loss of elongation reaches a minimum around 2 dpa.

NUREG\CR-6965

Effect of Irradiation Dose on Intergranular Fracture

15

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

333GBE304304LGBE304L327945GBE316623625690

GBE690C1C3C9C10C12C16C19C21

IG a

rea

fract

ion

(%)

Dose (dpa)

IG cracking starts to occur at a dose lower than that elongationreaches minimum.

SSRT Testing

16

0

20

40

60

80

100

0 5 10 15 20 25 30

Halden I, 0.4 dpaHalden I, 1.3 dpaHalden I, 3.0 dpaHalden II, ~2 dpa

Area

frac

tion

of IG

(%)

Uniform Elongation (%)

Resistant

NUREG/CR-6965, Halden Phase-II, Alloys 304, 304L, 316L, 690

Fracture Toughness Testing Results

17

0

100

200

300

400

500

600

0 2 4

J-In

tegr

al (k

J/m

2 )

Neutron Exposure (dpa)

SA and SMA weld HAZTested at ~290oC in NWC BWR env.

304 SMA HAZ, Thermally-treated at 500OC for 24 h

304L SA HAZ, as welded

304 SMA HAZ, As-welded 304L SA HAZ, thermally-treated

at 500OC for 24 h

0

200

400

600

800

0 4 8 12

JAPEIC BBJapeic CTJAPEIC SRGE CTVTT CT CF-8M_airC19C16SA HAZSMA HAZ304 SensitizedIT+GBEJ-

Inte

gral

(kJ/

m2 )

Neutron Exposure (dpa)

Austenitic SSs

ANL dataScatter band for fast reactor irradiations

304L SA HAZ and304 SMA HAZ

Fracture toughness data of as-welded and thermally-treated HAZs are within the scatter band.Thermal treatment may have improved the fracture toughness of irradiated 304 SMA HAZ at 0.75 dpa

18

Summary

While irradiation hardening and embattlement starts to appears at very low doses, the dose dependence of IG cracking shows a “threshold” behavior. IG cracking start to appear before the dose for that elongations reach minimum.

The post-irradiation strengths (YS and UTS) for the BOR-60 specimens were consistently lower than those of the corresponding Halden specimens. Likely related to Neutron spectrum and damage rate.

Fracture toughness data for irradiated SA and SMA HAZs are within the scatter band. Thermal treatment may have improved the fracture toughness of irradiated 304 SMA HAZ at 0.75 dpa

Future Work

High dose specimensSimulate PWR end of lifeInterest in samples from Zorita

SSRT testing at 10 and 40 dpaTEM specimens up to 40 dpa

19