PLiM Symposium in Shanghai

Structural Integrity Evaluation of Cast Austenitic Stainless Steel

Reactor Coolant Piping for Continued Operation of Nuclear Power Plants

PLiM Symposium in Shanghai

Structural Integrity Evaluation of Cast Austenitic Stainless Steel

Reactor Coolant Piping for Continued Operation of Nuclear Power Plants

2007년년년년 10월월월월 18일일일일

YOUNG JONG KIMGNEC

2007년년년년 10월월월월 18일일일일

YOUNG JONG KIMGNEC

11

INTRODUCTIONIIII

SUSCEPABILITY EVALUATIONIIIIIIII

CONCLUSIONIVIVIVIV

Contents

FLAW TOLERANCE EVALUATIONIIIIIIIIIIII

22

I . INTRODUCTIONI . I . INTRODUCTION

33

I . INTRODUCTIONI . I . INTRODUCTION

• NPP Life Extension - 40 years � 60 years, 48 NPP in the USA; - 30/40 years � 40/50 years in some European Countries

• In Korea, - 20 nuclear power plants (16 PWRs and 4 CANDUs) in operation. - Licensed design lifetime: Kori Unit 1(PWR) & 4 CANDUs: 30 yearsOthers: 40 years

• NPP life extension in Korea- 10 year extension is now under review for Kori Unit 1:- the first NPP in Korea, - operated since 29 April 1978.

44

Design ConditionsDesign Pressure: 2485 psigOperating Pressure: 2235 psigDesign Temp: 650°°°° F

Reactor Coolant Piping- two hot legs, - two cold legs and - two crossover legs

Reactor Coolant Piping of Kori Unit 1

55

Cast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issuesCast austenitic stainless steel thermal aging issues

fatigue crack growth Evaluation, flaw tolerance evaluationfatigue crack growth Evaluation, flaw tolerance evaluationfatigue crack growth Evaluation, flaw tolerance evaluationfatigue crack growth Evaluation, flaw tolerance evaluation

susceptibility susceptibility susceptibility susceptibility evaluationevaluationevaluationevaluation for thermal aging for thermal aging for thermal aging for thermal aging embrittlementembrittlementembrittlementembrittlement

reduction of fracture toughnessreduction of fracture toughnessreduction of fracture toughnessreduction of fracture toughness

CASS material CASS material CASS material CASS material ---- RCPB componentsRCPB componentsRCPB componentsRCPB componentsCASS material CASS material CASS material CASS material CASS material CASS material CASS material CASS material -------- RCPB componentsRCPB componentsRCPB componentsRCPB componentsRCPB componentsRCPB componentsRCPB componentsRCPB components

reactor coolant pipingreactor coolant pipingreactor coolant pipingreactor coolant piping

CASS( 14% to 20% ferrite)CASS( 14% to 20% ferrite)�� thermal aging thermal aging embrittlementembrittlement

to resolve the thermal aging issuesto resolve the thermal aging issuesto resolve the thermal aging issuesto resolve the thermal aging issues

fitting valve bodies, and reactor coolant pump casingfitting valve bodies, and reactor coolant pump casingfitting valve bodies, and reactor coolant pump casingfitting valve bodies, and reactor coolant pump casing

66

II. SUSCEPTIBILITY EVALUATIONII. II. SUSCEPTIBILITY EVALUATION

77

II. II. SUSCEPABILITY EVALUATION

Aubrey’s equationThe ferrite contents were calculated using chemical compositions in CMTR and Aubrey’s equation

the potential susceptibility was derived by comparing with the screening criteria of USNRC

Screening criterionfor a straight pipe < 20 % of ferrite contentfor a fitting and an elbow < 14 % of ferrite content

88

II. II. SUSCEPABILITY EVALUATION

18Static27.5-RC-B-11036 (35°°°°elbow)17Centrifugal27.5-RC-A-11036 (straight)16Static27.5-RC-A-1103 (35°°°°elbow)15Centrifugal27.5-RC-A-1103 (straight)

Coldleg

14Static31-RC-B-1105 (40°°°°fitting)13Static31-RC-B-1105 (90°°°°elbow)12Static31-RC-B-1105(90°°°°elbow with splitter)11Centrifugal31-RC-B-1105 (straight)10Centrifugal31-RC-B-1105 (straight)9Static31-RC-A-1102 (40°°°°fitting)8Static31-RC-A-1102 (90°°°°elbow)7Static31-RC-A-1102(90°°°°elbow with splitter)6Centrifugal31-RC-A-1102 (straight)5Centrifugal31-RC-A-1102 (straight)

Cross-over leg

4Static29-RC-B-1104 (50°°°°fitting)3Centrifugal29-RC-B-1104 (straight)2Static29-RC-A-1101 (50°°°°fitting)1Centrifugal29-RC-A-1101 (straight)

Hot leg

No.Casting methodSubparts (OD-system-loop-subcomponent no.)Piping

Specifications for Subparts of Reactor Coolant Piping of Kori Unit 1

99Non-acceptable< 1416.7218Acceptable< 1413.15

35°°°° elbows16

Acceptable< 2019.1717Acceptable< 2017.81

Straight pipesColdleg

15Non-acceptable< 1414.5814Non-acceptable< 1414.58

40°°°° fittings9

Non-acceptable< 1414.8113Non- acceptable< 1414.16

90°°°° elbows8

Acceptable< 1412.9912Non- acceptable< 1416.3490°°°° elbows

with splitter7

Acceptable< 2017.4211Acceptable< 2017.42

Straight pipe 210

Acceptable< 2014.166Acceptable< 2014.16

Straight pipe 1

Cross-over leg

5Acceptable< 1410.824

Non- acceptable< 1414.5850°°°° fittings

2Non- acceptable< 2021.093Acceptable< 2012.58

Straight pipesHot leg

1

SusceptabilityScreeningCriteria (Vol.%)

Ferrite Contents (Vol.%)

SubpartsNo.

Susceptibility Evaluation Results

II. II. SUSCEPTIBILITY EVALUATION

1 straight pipe and7 fittings/elbows potentially susceptible to thermal aging embrittlement

1010

III. FLAW TOLERANCE EVALUATIONIII. III. FLAW TOLERANCE EVALUATION

1111

III. III. FLAW TOLERANCE EVALUATION

Flaw Tolerance Evaluation Procedureto ensure the structural integrity of CASS reactor coolant piping subparts

NUREG-1801Two evaluation methods recommended - to demonstrate the integrity through enhanced volumetric examination- to perform plant specific and component specific flaw tolerance evaluation considering material property changes due to thermal aging embrittlement .

flaw tolerance evaluation proceduresand acceptance criteria for CASS piping - ASME Code Section XI , IWB-3640.

1212

Flow Chart for Flaw Tolerance Evaluation Procedure

StartStartStartStart

Crack ConfigurationCrack ConfigurationCrack ConfigurationCrack Configuration

Axial Surface CrackAxial Surface CrackAxial Surface CrackAxial Surface Crack Circ. Surface CrackCirc. Surface CrackCirc. Surface CrackCirc. Surface Crack

Stress Distribution CalculationStress Distribution CalculationStress Distribution CalculationStress Distribution Calculation

Stress Intensity Factor (KStress Intensity Factor (KStress Intensity Factor (KStress Intensity Factor (KIIII) ) ) )

Calc.Calc.Calc.Calc.

Fatigue Crack Growth Fatigue Crack Growth Fatigue Crack Growth Fatigue Crack Growth EvaluationEvaluationEvaluationEvaluation

Crack GrowthCrack GrowthCrack GrowthCrack Growtha = a + a = a + a = a + a = a + dadadadac = c + dcc = c + dcc = c + dcc = c + dc

Crack DepthCrack DepthCrack DepthCrack Depth> > > > AccepAccepAccepAccep. . . . CriteriaCriteriaCriteriaCriteria

EndEndEndEnd

Stress AnalysisStress AnalysisStress AnalysisStress AnalysisResultResultResultResult

YesYesYesYes

NoNoNoNo

Crack Evaluation Crack Evaluation Crack Evaluation Crack Evaluation At end of lifetimeAt end of lifetimeAt end of lifetimeAt end of lifetime

III. III. FLAW TOLERANCE EVALUATION

1313

Hot Leg Stress Analysis ResultsPiping Load Stress in Elbow Region

Unit: Pa

III. III. FLAW TOLERANCE EVALUATION

1414

Crossover Leg Stress Analysis ResultsMaximum Pressure Stress

Axial Stress Hoop Stress Unit: Pa

III. III. FLAW TOLERANCE EVALUATION

1515

Cold Leg Stress Analysis ResultsMaximum Pressure Stress

Axial Stress Hoop Stress Unit: Pa

III. III. FLAW TOLERANCE EVALUATION

1616

Fatigue Crack Growth Equation

( )( )45.0max

11 1101465.5da/dN RK −×= −

a = Crack depth (in)N = Number of cyclesR = Kmax/KminKmax ,Kmin= Maximum and minimum stress intensity factor(ksi-in1/2)

- EPRI(1000976; 2001) Fatigue Crack Growth Equation- PWR primary water environment test(320°C)- Upper Bound Curve for all the crack growth data

III. III. FLAW TOLERANCE EVALUATION

1717

o ASME XI, Appendix L, L-3200(Table L-3210-1)

Initial Crack Assumption

* Aspect Ratio(6:1)

III. III. FLAW TOLERANCE EVALUATION

1818

III. III. FLAW TOLERANCE EVALUATION

Hot Leg Fatigue Crack Growth Evaluation (axial)Crack depth at end of life=0.42 in=10.67 mm

mMPainksiK I 1.175.15life) of (end ==

1919

Hot Leg Fatigue Crack Growth Evaluation (circumferential)Crack depth at end of life=1.12 in=28.45 mm

III. III. FLAW TOLERANCE EVALUATION

mMPainksiK I 3.274.28life) of (end ==

2020

Final Axial Crack Depth for CASS Piping Subparts

14.8110.1612.698.712268.5835°°°° elbowColdleg

14.6711.1811.78.915476.290°°°° elbow

with splitter

14.6711.1811.78.915476.290°°°° elbow14.010.6711.78.915476.240°°°° fitting

Cross-overleg

14.4410.2712.368.788471.12Straight pipe At the

maximum hoop stress

generation location

in each subpart

15.010.6712.368.788471.1250°°°° fittingHot leg

Depth ratio (%)

depth(mm)

Depth ratio (%)

Depth (mm)

Crack locationcalculated

Final crackInitial crack Pipe Thick-ness

Subparts

III. III. FLAW TOLERANCE EVALUATION

2121

III. III. FLAW TOLERANCE EVALUATION

Failure mode Evaluation- ASME B&PV Code, Sec.XI, App.C, Article C-4000- failure modes of almost all subparts : FPF- fully-plastic fracture (FPF) � ductile fracture (DF), because tensile property may increase, while fracture toughness may decrease due to thermal aging embrittlement.

2222

Failure Mode Evaluation Results for Axial Cracks

DF (EPFM analysis)0.27216434.6135°°°° elbowColdleg

FPF (limit load analysis)0.19618720.8490°°°° elbow with splitter

FPF (limit load analysis)0.19618720.8390°°°° elbow

FPF (limit load analysis)0.19218720.5140°°°° fittingCross-overleg

FPF (limit load analysis)0.175203.520.29StraightPipe

FPF (limit load analysis)0.177203.520.5550°°°° fittingHot leg

RemarksSC(=K’r/S’r)

Min. fracture toughness

KIc(MPa m0.5)

Max. SIF at final crack size

KI-max(MPa m0.5 )Subparts

Note) FPF if SC<0.2; DF if 0.2≤≤≤≤SC<1.8

III. III. FLAW TOLERANCE EVALUATION

2323

Flaw Tolerance Evaluation Results for Axial Cracksthe results of flaw tolerance evaluation for axial cracks at the end of continued operationstructural integrity of CASS RC piping be maintained over 40 years

0.440.14835°°°° elbowCold leg

0.70.14790°°°° elbow with splitter

0.70.14790°°°° elbow0.70.14040°°°° fitting

Cross-over leg

0.70.144Straight pipe Structural integrity

will be maintained over the continued operation period.

0.70.15050°°°° fittingHot leg

RemarksAllowable

crack depth ratios

Evaluated crack depth

ratiosSubparts

III. III. FLAW TOLERANCE EVALUATION

2424

IV. CONCLUSIONIV. IV. CONCLUSION

2525

CONCLUSIONCONCLUSION

integrity evaluation of CASS RC piping of Kori Unit 1considering the change of material properties due to thermal aging embrittlement.

predicted fatigue crack growths- not significant for all CASS RC piping.

final crack sizes (40 years) - satisfied in accordance with the ASME Section XI acceptance criteria.

structural integrity of CASS reactor coolant piping- maintained over 40 years.

Thank you very much.Thank you very much.