Steam Generator Management Strategies in Korea

Steam Generator Management Strategies in Korea

Seong Sik Hwang, Hong Pyo KimKorea Atomic Energy Research Institute

Consultancy Meeting on Update of IAEA-TECDOC on Ageing Management of Steam Generators

IAEA, Vienna, AustriaJune 15-18, 2009

2

ContentsContents

1. Background (Korean Nuclear Power Plants)

2. SG tube degradation history in Korea

3. SG drain nozzle cracking

4. Implementation of SGMP* in Korea

5. Issues in Korean SG

6. Summary

SGMP: Steam Generator Management Program

3

BackgroundBackground

Nuclear Power Plants in Korea: 20 units

16 PWRs, 4 PHWRs

35.5 % of total power generation in 2009 is from nuclear

Corrosion problem in steam generator tubings

Cracking in Alloy 600 nozzle

4

6th biggest nuclear capacity in the world

Korean Electricity SystemKorean Electricity System

Source: J. Ha(KAERI) “Korean Nuclear Technology Past, Present and Future”, Mar.2009

5

`In operation

20 units(17,716 MW)

`Underconstruction

8 units(9,600 MW)

`Underplanning

10 units(15,400 MW)

Yong-gwang6 units

Kori8 units

Ulchin8 units

Wolsong6 units

In OperationUnder Construction

Nuclear Power Plants in KoreaNuclear Power Plants in Korea

Source: J. Ha(KAERI) “Korean Nuclear Technology Past, Present and Future”, Mar.2009

Site In Operation Under Const. Total

Kori 4 (3,137) 4 (4,800) 8 (7,937)

Wolsong 4 (2,779) 2 (2,000) 6 (4,779)

Yonggwang 6 (5,900) - 6 (5,900)

Ulchin 6 (5,900) 2 (2,800) 8 (8,700)

Total 20 (17,716) 8 (9,600) 28 (27,316)

(As of 30 Jan., 2009, Units: MW)

6

Nuclear power plants under constructionNuclear power plants under construction

http://www.khnp.co.kr/eBook/khnp_ebook_en.pdf

7

Plant K-1K-2,3,4 &

Y-1,2Y-3~6,U-3,4

U-1,2 U-5,6 W-1~4

Manufacture Westinghouse Westinghouse Doosan Frammatome DoosanF & WB & W

Model Delta 60 F CE S-80 51B CE S-80 CANDU

TubeMaterial

Alloy 690TT Alloy 600TT Alloy 600HTMA Alloy 600TT Alloy

690TTAlloy 800

TubeExpansion

Hydraulic Hydraulic ExplosiveHard roll+ Kiss roll

ExplosiveHard rollHydraulic

Status of Korean Nuclear SGs

Source: NETEC in Korea

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SG tube Degradation History in Korea

9

Stress Corrosion Cracking, SCC Pitting Denting Wastage, Wear Fretting Corrosion Fatigue Loose parts

Types of corrosion in S/GTypes of corrosion in S/G

10

Degradation mechanismsSecondary SidePrimary Side

SCC

A B

A-B

Steam outlet

Primary coolant outlet Primary coolant inlet

Anti-vibrationbars

Tubesupportplate

Tubesheet

SCC

Fretting/Wear

Wall thinning

IGA

IGA

SCC

Pitting

SCC

U-bend

Inside Tubesheet

Top of Tubesheet

by S.S.Hwang of KAERI

Denting

Sludge pile

11

Fig. Schematic view of four intrinsic modes of corrosion[after R.W.Staehle]

Schematic modes of corrosion in S/GSchematic modes of corrosion in S/G

12

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03

0

20

40

60

80

100

IGA Impingement Pitting Fatigue Unkown Other Wear Thinning SCC Preventive

IGA Impingement FatiguePitting

Revised by KAERI 10/13/2003, File:E:SG/sginformation/worldplug/worldplug2003.opj (after EPRI progress report)

Other

Wear

SCC

Unknown

Preventive

Thinning

Fig. Worldwide causes of steam generator tube plugging

Perc

ent

Year

Worldwide Causes of tube pluggingWorldwide Causes of tube plugging

13

78 80 82 84 86 88 90 92 94 96 980

20

40

60

80

100 File:D:/sg/sginformation/koreanplug.opj(Jul.2001, SSHwang)

Korean causes of steam generator tube plugging (From KINS/AR-669)

Per

cent

age

Year

Wastage Denting Pitting ODSCC IDSCC Fretting Fatigue Erosion Others

Causes of tube plugging in KoreaCauses of tube plugging in Korea

14

A B C D E F G H I J K L M N0.0

0.5

1.0

1.5

2.0

2.5file:D/paper/99aging/orids4/plugratio.opj

Pl

ug ra

tio, %

Plant

Tube plugging in Korean Tube plugging in Korean NPPsNPPs

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Corrosion environments in S/GCorrosion environments in S/G

1) Acidic environment- Sea water ingress

MgCl2 + 2H2 O = MgOH + 2HCl- Sulfate ingress

SO42- +H2 O = HSO4- + OH-

HSO4- = SO42- + H+

- Phosphate[Na+]/[PO4

3-] <2.3

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2) Caustic environment

- Ingress of Na+ , Volatile anion

- Selective evaporation of anion

Na+ concentration in crevices

NaOH environment in the crevices

Corrosion environments in S/GCorrosion environments in S/G

17

Background:April 1989, S/G A, B cold leg, 3 tubes extracted.

Type of corrosion: Pitting (Alloy 600 LTMA)

Pit penetration through the tube wall, 94 %.

Causes: Acidic chloride and sulfate due to condenser leakage. High oxygen level due to condenser leakage Copper from secondary side materials. Concentration of aggressive ions(104~ 105 times of bulk).

Countermeasures: Suppress the ingress of impurities, control of oxygen, Sludge removal, Chemistry guide line, Database of ECT

Pitting Plant APitting Plant A--19891989

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Pitting at plant APitting at plant A--19891989

S/G B Cold leg R28C53 (Alloy 600 LTMA)

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Background : May 1990, S/G B hot leg, 2 tubes extracted. Type of corrosion: TGSCC, Pitting (Alloy 600 TT) Pit penetration through the tube wall, 96 %, Crack penetration through the tube wall, 23 %. Causes:

Lead, Denting at TTS

Countermeasures: Sludge removal, Reduction of oxygen,Elimination of lead source, on line monitoring system

Lead SCC Plant BLead SCC Plant B--19901990

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TransgranularTransgranular SCC at plant BSCC at plant B

S/G B Hot leg R16C61 (Alloy 600 TT)

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SSRT in solution with lead SSRT in solution with lead

(a)

(b)

Fig. SEM micrographs of fracture surface of Alloy 600 MA (a) 0.01% C, 100 ppm Pb, 1x10-7 sec-1, 340oC, pH 10(IGSCC) (b) 0.04 %C, 5,000 ppm Pb, 1x10-6 sec-1, 340oC, pH 10(TGSCC)

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Main source of leadMain source of lead

Metallic streaks from lead mallets (Turbine)

Radiation shielding materials

Babbit alloys(Bearing)

Greases and lubricants(Pump)

Seals and gasket (Valve packing)

Preservatives and paints(Liner coating)

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Background : Nov. 1992, S/G A, B hot leg, 3 tubes extracted. Type of corrosion: PWSCC, Pitting and denting (Alloy 600 LTMA Pit penetration through the tube wall, 44 %, Crack penetration through the tube wall, 56 %. Causes:

Materials, Temperature, Primary water chemistry

Countermeasures : Stress relieving treatment, Shot peening,Primary water temperature reduction

PWSCCPWSCC Plant APlant A--19921992

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PWSCC at plant APWSCC at plant A

S/G A Hot leg R11C45 (Alloy 600 LTMA)

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Background : Nov. 1994, S/G C hot leg, 2 tubes extracted. Type of corrosion: PWSCC (Alloy 600 TT) Crack penetration through the tube wall, 99 %. Causes:

Materials, Temperature, Primary water chemistry

Countermeasures : Crack length based plugging criteria,Ni plating, Sleeving, Shot peening, Primary water temperature reduction

PWSCC Plant CPWSCC Plant C--19941994

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Background : Aug. 1995, S/G A hot leg, 1 tube extracted. Type of corrosion: ODSCC, IGA (Alloy 600 LTMA) Crack penetration through the tube wall, 100 %. Causes:

Caustic environment High copper High oxygen

Countermeasures : Crevice flushing, TiO2 addition, Control of dissolved oxygen, Power reduction to 85%,Na/Cl ratio control.

ODSCC Plant AODSCC Plant A--19951995

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ODSCC at plant AODSCC at plant A

S/G A Hot leg R27C34

3

2

1

1 2 3

(Alloy 600 LTMA)

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0 50 100 150 200 2500

10

20

30

40

50

60

70

80

90

100

Area 3 Area 4Area 2Area 1

file:D:/paper/99aging/k1sludge.opj

Oxygen Cr Fe Ni Cu

Con

tent

s, W

t%

Distance from interface between sludge and water, m

Analysis of scale collected from plant AAnalysis of scale collected from plant A

1234

S/G A Hot leg R27C34

Cu

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PWSCC Plant CPWSCC Plant C--19991999

Background : Jan. 1999, S/G C hot leg, 3 tubes extracted. Type of corrosion: PWSCC (Alloy 600 TT) Crack penetration through the tube wall, 100 %. Causes:

Sensitive material (alloy 600) Countermeasures :

10 liter/hour of Leak permission. Detail inspection on selective area

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Plant CPlant C-- Schematic of the ‘Kiss roll’

22.22 mm19.68 mm

0.38 mm(FRAMATOME)

22.60 mm

PWSCC

~ 0.12 to 0.16(EdF) =0.15 (TRACTEBEL)

~ 19

mm

(Alloy 600 TT)

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Plant CPlant C-- S/G C hot leg, R13C34(tube A)

1.66

6.62

2.50

4.98

2.50

4.98

1.67

5.79

2.49

5.71

2.50

5.80

0

1

2

3

4

5

6

7

8

9

10

0 90 180 270 360

결함위치, de g결

함길

이,

mm

D4 D3(D7) D2 D1 D6 D5

#2#7#3#4

2.98mm5.28mm 2.77mm2.59mm

#1 #5#6

4.56mm 4.0mm3.89mm

ECT collected by KPS, analyzed by KAERI

#4#4#5#5 ##

66#1#1

#2#2 #3#3

Max voltageMax voltage 8.028.02 4.934.93 3.953.95 9.349.34 5.705.70 8.528.52

(Alloy 600 TT)

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Plant DPlant D--2002

Background : May. 2002, S/G B hot leg, 3 tubes extracted. Type of corrosion: PWSCC- tube rupture (Alloy 600 HTMA) Crack penetration through the tube wall, 100 %. Causes:

Bulge during tube installation

Primary water chemistry

Countermeasures :

Improvement of process document of tube expansion

Improvement of pre service inspection on top of tube sheet

Improvement of third part evaluation on non destructive examination

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Plant D Plant D --2002 (cont.)2002 (cont.)

Steam Generator Tube Rupture

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Plant EPlant E--2003

Background : Dec. 2003, S/G #2 hot leg, 2 tubes extracted. Type of corrosion: ODSCC (Alloy 600 HTMA) Crack penetration through the tube wall, 100 %. Causes:

Tube dent Countermeasures :

Survey on irregularity of expansion region, Survey on dent signal

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Remedial measures consideredRemedial measures considered

Plugging

Sleeving

Crevice modification

Surface modification

Chemical cleaning

Chemical mitigation

Reduced ‘hot leg’ temperature

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PWSCC in SG Drain Nozzle

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Boric acid precipitation at Boric acid precipitation at Plant Plant --2 SG Drain Nozzle2 SG Drain Nozzle

Inspected on May 27, 2008

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Nozzle (Alloy 600) ExtractionNozzle (Alloy 600) Extraction

215

mm

Carbon steel(Alloy 508)

Stainless steel cladding(Type 309)

18.78mm29.64mm

CracksButter(Alloy 82/182)

Weld(Alloy 82/182)

To view of Part A

cracked area 40 mm long

Part A

Part B

Noncracked area 20 mm longPart B

SG Drain NozzleSG Drain Nozzle

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#6 #4

270O 90O

180O

A1

A2

#8#3

#6

#11 #10#5#9#4

#7

#13

#12

0O

Crack OpeningCrack Opening

100 % through wall 100 % through wall

SG Drain NozzleSG Drain Nozzle

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ID crack detailID crack detail--No 3 crackNo 3 crack

Crack No. 3

Ductile ligament->ID initiated Crack

ID initiated 70 % TW Cracking

IDOD

Brittle intergranular SCC fracture-> PWSCC

Ductile ligament

270O 90O

180O

A1

A2

#8#3

#6

#11 #10#5#9#4

#7

#13

#12

0O

No evidence of fatigue on the fracture surfaceNo evidence of fatigue on the fracture surface

SG Drain NozzleSG Drain Nozzle

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Initiation and PropagationInitiation and Propagation--No 4 crackNo 4 crack

16.0 mm26.7mm

30m

m

22.4

mm

Cracks

18.5

mm

gro

und

out

0O90O

A1

9.72mm

12.89mm

Crack No 4

Top of slope

Bottom of slope

15.00mm

5.3mm

7.0mm

4.1 mm

IDOD

6th Cut

8.5 mm

360O

Gound Out while nozzle pulling

270O

ID surface viewDia 18.49

Dia 16.0

On site ECT

Metallography

12 mm(ECT)

From weld root to up and downFrom inside to outside

SG Drain NozzleSG Drain Nozzle

42

Repair of the drain nozzle with alloy 690

Base metal(Alloy 508 Class 3)

Stainless steel cladding(Type 309L)

Butter(Alloy 82/182)

Weld(Alloy 52M/152

Full depth nozzle repair with alloy 690

Alloy 690

SG Drain NozzleSG Drain Nozzle

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Two PWSCC incidents in SG drain nozzles(2007, 2008)

Not bad carbon contents, well developed drain boundary carbides (No major reason from material itself)

Axial ID cracks were characterized. (Circum. cracks were ground out during pulling)

No evidence of fatigue fracture

Cracks initiated from weld root, grew upward and downward.

Intergranular fracture surface, ID initiated ->PWSCC

Two cracks penetrated the nozzle wall

No profound Sulfur content in the precipitates

Precise residual stress analysis is needed.

Crack Analysis ResultsSG Drain NozzleSG Drain Nozzle

44

Implementation of SGMP* in Korea

Source: NETEC in Korea

SGMP: Steam Generator Management Program

45

Implementation of SGMP in Korea

Developed Korean SGMP guidelines

An integrated document based on NEI 97-06 guidelines and the accompanying EPRI guidelines

Organizing and training SG program staff

Approved by the Korean regulatory body

Being implemented since 2005

Source: NETEC in Korea

SGMP: Steam Generator Management Program

46

Current SG Sampling and Inspection Requirements

Came from SGTR event of Ulchin unit 4

Required to comply with regulatory bulletin requirements

Preparing SG Sampling and Inspection Plans

Related with EPRI guidelines : Examination and Integrity assessment

Under review by the Korean regulatory body

To be approved by the end of this year(2009)

Plan to apply to all Korean Nuclear Power Plants

Source: NETEC in Korea

Sampling and Inspection Plans for SG TubingSampling and Inspection Plans for SG Tubing

47

Developed at 2005 for implementation of SGMP in Korea

Reviewed in accordance with revised EPRI guidelines

NEI 97-06 rev.2

SG Integrity Assessment Guidelines revision 2

The New Performance Criteria

Important Definition to the Performance Criteria

SG Examination Guidelines revision 7

SG In-Situ Pressure Test Guidelines revision 3

Under review by Korean regulatory body for approval

Revision of Korean SGMP GuidelinesRevision of Korean SGMP Guidelines

Source: NETEC in Korea

48

Issues in Korean SGIssues in Korean SG

Source: NETEC in Korea

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Flaw Indications with Alloy 600TTFlaw Indications with Alloy 600TT

Reported some circumferential flaw-like indications on W/H Model-F SG with Alloy 600 TT tubing

Kori unit 2, SGB R57C71

Special issues : No dent, No sludge Need to confirm a flaw or not EPRI peer review suggested 4 indications meet flaw criteria

among seven

ODSCC with Alloy 600TT at TTS

Source: NETEC in Korea

TTS: Top of Tube Sheet

50

General Information in Ulchin unit 3 1000MW PWR CE 2-Loop NSSS Explosive full-depth tube sheet expansions Egg crate tube supports plates Commercial operation since 1998(9.18EFPY)

Main degradations AVB Wear SCC at top of tube sheet

Source: NETEC in Korea

Axial ODSCC with Alloy 600 HTMA

Identified Axial ODSCC at Tube support Plates

51

Upper Bundle Hydraulic Cleaning

On Spring, 2007, YG unit-2, 16th refueling outage

Cleaned the upper bundle of quatrefoil-broached TSP

Using KULAN cleaning system

Advanced Scale Conditioning Agents (ASCA)

A full-bundle ASCA maintenance cleaning has been performed at Kori unit 3,4

On Summer, 2007, Kori unit-4 refueling outage

Source: NETEC in Korea

Sludge Removal

52

Chemical Cleaning on OPR1000 SG

Overview of YG unit-3 chemical cleaning

The accumulation of deposit in the secondary side of SG can lead to tube corrosion or operational problems

SCC at TTS is a main degradation of YG unit 3

The tube lancing efficiency of CE SG was low

Narrow distance between tubes

Applied chemical cleaning to remove hard sludge at TTS

During YG unit 3, 11th refueling outage

Applied EPRI SGOG techniques

Partial chemical cleaning process

Source: NETEC in Korea

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Current Repair Criteria

Source: KINS in Korea

Plant (S/G) Current Repair Criteria Remarks

Kori-1,2,3,4,YG 1,2(WH)

. Defect depth ≥40% of TW

. Plugging all cracked tubes Based on ASME Sec.XI, IWB-3521

UC 1,2(Framatome)

. Defect depth ≥ 40% of TW

. Axial cracks : Lenght ≥ 13㎜

. Circum. cracks : Plugging orsleeving

Axial crack: Framatome Std.

YG3,4,UC 3,4 (KHIC)

. Defect depth ≥ 40% of TW

. Plugging all cracked tubes Based on ASME Sec.XI, IWB-3521

WS 1(FW),WS 2,3,4(KHIC)

. Defect depth ≥ 40% of TW

. Plugging all cracked tubesBased on ASME Sec.XI, IWB-3521

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Developing of ARC is a matter of concern in KHNP

Indications meeting the required distance within tube sheet may remain in service regardless of its orientation and severity

RPC inspection is not required below the specified distance

AlternativeAlternative Repair Criteria (ARC)

Source: NETEC in Korea

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Plants SG Characteristics ARC

K-2~4Y-1,2

W/H Model FAlloy 600TT

Hydraulic

H* (TTS-3~9”)B* (TTS-17”)

U-1,2Framatome 51B

Alloy 600TTKiss roll

F* (TTS-2”)

Source: NETEC in Korea

ARC in Korea

AlternativeAlternative Repair Criteria (ARC)

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SummarySummary

Various types of corrosion in steam generator tubes at Korean NPPs (Pitting, PWSCC, ODSCC, IGA, Denting)

Proper countermeasures to combat the problems (Reduction of Cl-, Oxygen, Temperature reduction of primary side, Molar ratio control, Inhibitor, Water chemistry guideline)

PWSCC in alloy 600 SG drain nozzle

Implementation of SGMP in Korea, and will be revised near future.

SG tubing sampling inspection strategy will be modified according to the SGMP requirements.

ARC within tubesheet, Axial ODSCC at tube support plate, Sludge removal and control are considered.