ML20199G953
| ML20199G953 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/31/1998 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| Shared Package | |
| ML20199G930 | List: |
| References | |
| BAW-10226, BAW-10226-R01, BAW-10226-R1, NUDOCS 9802040375 | |
| Download: ML20199G953 (132) | |
Text
{{#Wiki_filter:. _ . . . _ _ - . _ . . . . . _ . . BAW-10226 Rev.1 January 1998 ALTERNATE REPAIR CRITERIA FOR , VOLUMETRIC OUTER DIAMETER INTERGRANULAR ATTACK IN TIIE
, TUBESilEETS
^ OF ONCE-TIIROUGli STEAM GENERATORS e Prepared for B&W Owners Group Steam Generator Committee 4 4 Prepared by: Franatome Technologies, Inc. P.O. Box 10935 Lynchburg, Virginia 24506-0935
;"J" 188 2 3!8 sal a P PDR.
This document is the non-proprietary version of the proprietary document BAW-10226P Revision 1. In order for this document to meet the non-proprietary criteria, certain blocks of information were withheld. The basis for determining what information to withhold was based on the criteria listed below. (b) The infonnation reveals data or material concerning B&WOG research or development plans or programs of potential economic advantage to the B&WOG. (c) The use of the information by a non member would decrease his expenditures, in time or resources, in designing, producing, or marketing a similar product. (d) The information consists of test data or other similar data concerning a process, method, or component, the application of which results in an economic advantage to the B&WOG. (e) The information reveals special aspects of a process, method, component or the like, the exclusive use of which results in an economic advantage to the B&WOG. BAW-10226 Rev.1 ii
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. RECORD bF REVISION i l
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- Rsvision - Date - - Section.-
Description
- OriginalIssue Sections 1 through 4 released for +
.. 0 -8/14/97 4- -
NRC review , -1 1/27/98 All' : Complete Revision 1 4 i i e-i A A d 1~ r 4-r. h , iBAW 10226 Rev 1 . : iii . l" - , , ..-, ,+, y , - , ,
EXECUTIVE
SUMMARY
4 This report documents the technical justification to implement an alternate repair criteria (ARC) for volumetric outer diameter intergranular attack (ODIGA) in the tubesheet regions of B&W Once Through Steam Generators (OTSGs). This assessment demonstrates that a repair limit based on bobbin coil voltage can be used to conservatively satisfy the Regulatory Guidelines for tube integrity in OTSGs. Numerous tasks were performed to develop the technical basis for the ARC. The flaw morphology and EC characteristics of volumetric ODIGA were defined based on tube pull data and were utilized to create laboratory samples. Leak testing of the laboratory j samples at MSLB conditions showed no iveakage for any of the samples tested and showed no susceptibility to tensile rupture at loads up to [ ]d times MSLB conditions. Testing of 100%TW holes showed that the presence of the tubesheet precludes tube burst in the tubesheet. Freespan burst testing of the IGA samples resulted in burst pressures more than twice the Reg Guioe 1.121 requirements. Evaluation of field IGA over three inspections (2.8 EFPY) resulted in a bounding growth rate of [ ]d volts /EFPY. The results from these tasks were combined with appropriate EC acquisition and analysis
.;chniques to develey an appropriate repair criteria.
Requirements for ARC Implementation The following requirements for ARC Implementation conservatively satisfy Regulatory Guidelines for tube integrity:
. Site specifis confirmation of damage mechanism must be made by the destructive examination of pulled tubes.
- A site specific growth rate analysis must be performed prior to implementation. If it is determined that there is not enough data available to determine a growth rate, appropriate OTSG industry data will be utilized.
- Outer Diameter (OD) indications less than the voltage repair limit, as measured by bobbin coil, and confimied volumetric by rotating coil (RC), may remain in service.
- OD indications greater than the repair limit, as measured by bobbin coil, will be repaired or removed from service.
- The ARC will be applied to volumetric TS indications located in the tube span
[
]'
- The implementing site must have a MSLB maximum tensile tube load of no greater than [ j' LB based on current ARC leak testing.
BAW-10226 Rev.1 iv
Inspection Requirements
- During each outage that the TS ODIGA ARC is implemented,100% bobbin coil inspection of the in-service unsleeved tubes in the applicabla TS region (s) will be conducted in accordance with the requirements of Appendix A.
- All OD bobbin coil indications located in the tube span [
l'
. Tubes with indications that are confirmed to be crack like will be repaired or removed from service. . .abes with indications confirmed volumetric by RC will be dispositioned by the ARC.
- Indications with bobbin coit voltages less thc.n or equal to the repair limit will be left ir. servict
- Indications greater than the repair limit will be repaired or removed from Service.
- During the first outage the ARC is applied, in-situ leak testing of a sample of the largest voltage ODIGA flaws will be performed to validate the results of testing performed on laboratory samples.
BAW-10226 Rev.1 y
TABLE OF CONTENTS
- R E CO RD O F REV I S I ON . . ... .. .. ... . .. . . . . .. . . . . . . .. . . . . . . . . . . . ... .. . . . .. .. .. . .. . .. .. . . . . . . ..... .. . . . . ... ... .
EX ECU TIV E SU M hf A RY . . . . . . . . . . .. . . . . . . . .. . . . . . .. . . . . .. . . . . . . . . . . . .. . . ... . . ... . . . . . . . .. . . . . . . . . . . . . A C RONYhiS AN D ABB REVI ATl ON S .......................... ................................................ xi i.0 1 N T R O D U C T10 N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Purpose............................................................................................................I 1.2 Background....................................................................................................I 2.0 ' D ES C R I PTI ON O F OTS G . . . . . . . . .. . . . . ... .. . . . . . . . .. . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . ... . .. . . . . . 2.1 Functi c nal De scription . . . . . .. . . . . .... . ..... . . . . . . . . . . . .. . . . .. . . . . .. . . . . . .. . . . . . . . . . .. .. . . . . . . . . . . . . . . . 3 2.2 De si gn I n fo rm at i on . . .. . . . . . . . .. . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . .. . . . . . . . . . . . 2.3 Tube M ate ri al Propert i es .. .. . ... . . .. . .. . . . . . . ... . .. . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . .. . . . . .. . . .. . . . 4 2.4 Co nc l u s i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 A S S ES S h1 ENT OF O DIG A .... ... .. .. ........ ...... .. . ........ . .... ...... . .... .. ... .. . . ... .... 8 3.1 Backgreund..................................................................................................8 3.2 Secondat y Side Chemistry Control ...... ................................. ..................... 9 3.2.1 RSG and 10TSG Operating Features Affecting Chemistry Control ............... 9 3.2.2 OTS G C hem istry Control . .. . .. . . . .. .. .. . . . . .. . . .. . . . .. . . . . . .. ... . . . . . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . 9 3.2.3 Summary of Secondary Chemistry Evaluations..... ................... ................. 10 3.3 Morphology o f Pulled Tubes .. . ... .............. . .. ..... ..... .. ..... .. ... .. .. . .. ......... ... .. .... ... I 1 3.3.1 [ )*...................................................................................................12 3.3.2 [ )*......................................................... ..........................................14
'3.3 [
)*....................................................................................................16 3.3.4 [ 1*...................................................................................................17 3.3.5 Plant.to. Plant Comparison and Morphology Summary...... . ....... ............... I S 3.3.6 Conclusions on Flaw Morphology ..................... ........... ............ .. . . ......... 20 3.4 EC o f P ul l ed Tubes . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .
3.4.1 ODIGA.......................................................................................................26 3.4.2 Characterization of Crack-Like vs Volumetric Morphologies..................... 31 3.4.3 Summary of EC Response Relative to Flaw Morphology .............. .. ......... 34 3.5 Summary and Conclusions, OTSG ODIGA Flaw Morphology............ ...... 34 3.6 References....................................................................................................35 4.0 LA B ORATORY ODIG A FOR ARC .................... ... .................................. 3 6 4.1 I nt rod u c ti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 K e y Param e t e rs . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Laboratory Sample Fabrication ... . .... ........................................................ 3 7
~4.4 Results of Laboratory Sample Evaluation Program......................... ........... 37
'4.4.I Destructive Examination Results ............................... ..................... ......... . 3 7 4.4.2 Eddy Current Evaluation R esuits .. .......... .................. .. .......... .... .... . .. .. 39
. BAW-10226 Rev.1 vi
1 l l 4.5_ Summary and Conclusions, Laboratory Sample Evaluation....................... 46 5.0 STRUCTURAL EVALUATION OF TUBESHEET ODIGA. ................... 47 5.1 I n trod u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . 5.2 Tubesheet Interface ARC Exclusion Zone ................................................... 47 5.3 B urst Rupture Eval uation ................... .... .................. .. .................. . ...... . ... ... 4 8 5.4 Tensile Rupture Eval uation ..... ........... ............ ............ .. . . ... ... ... .... .. . ..... .... 4 9 5.5 Fati gue Eval uati o n .. . .. . ... .. . . . . ... . . .. . . . . . . . . . . . ... . . . . . . . . . . . . . . .. . . . . . .. .. . . . . . .. .. . . . . . . . . . . . . . . . . . 4 9 5.6 Summary of Structural Evaluations of Tubes Affected with ODIGA ........ 50 5.7 R e fe re n c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.0 E D DY C U RRENT TEC HN IQ U ES ............ ................................................ 51 6.1 I n t rod u c ti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 B a c k g ro u n d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 A R C De velopme nt EC . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . .. . . ................51 6.3.1 Laboratory Sample EC Process .......................... ......... ........ ............. ...... 51 6.3.2 Ed d y C u rre n t Eq ui pm e nt . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 6.3.3 Cal ibrat ion Standards . . .... . ....... . . . . .. .. ... . ............ . . ...... . ..... . . . . ...... .. ... .. . ..... . 5 2 6.3.4 Ac q u i sit i o n Param e te rs .. .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 5 2
- 6. 3.5 A n alysis Techniq ue .. . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . .. .. . . . . .. . . . . . . . . . . . 5 3 6.3 . 6 A nalysi s Proc e ss . . . .. . . . . .. . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . ... . . . . . . . . . . . . .. . . . . . . . . . . . . .
6.3.7 Normalization of Calibration Standards to ARC " Mother-Standard".......... 53 6.3.8 Normalization of Previous EC Data for ARC Purposes........... ............. ..... 55 6.3.9 Approach for EC Uncertainty.... ........................................................ .... .... 5 7 6.4 ARC EC Field Implementation ...... ................ .......... ........................ . ... 60 6.4.1 B obbi n Coil Probes . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . ...... 60 6.4.2 Ro tati n g Co il Probes . . .. . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. 61 6.4. 3 Calibration Standards . ...... ..... .. .. . . ...... . ...... .. ...... . .. . .. ... . . ..... .. . . ... ... . .. . . . . . .. 61 6.4.4 Acq uisi tio n Parameters . .. ..... . ... . . ... .. . ... .. . . . .. ...... .. . . .. ... . .... ... .. . . . . . . . 61
- 6.4. 5 Ana lys i s Tec hni ques . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . 6 2 6.5 R e fe re n c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.0 LEAKAGE EVALUATION OF TS ODIG A.............. ............... ................ 64 7.1 I nt rod u c ti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Development of Botmding Leak Test Conditions.......... .. ....... ..... ............ 64 7.3 Hot Leak Testing Syste:n Description.............. ................ ...... . ................. 65 7.4 Leak Test P rogram . . ... . . . .. . . .. . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . .. .. . . . . . . . . . . . . . . 6 6 7.4.1 E D M Te sti n g .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6
- 7.4.2 . Laboratory Sample Testing .............. . ........................ ..... ..... .. .. . ....... . .. ..... .. . 67 7.5 Summary and Conclusio ns .... .. . ......... .. . ... .... ........ ...... . .. .. .. .. . . . ... . ...... . .. . ... . . ... 6 8 7.6 R e fere n ce s . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 BAW-10226 Rev.I vii
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; 8.01 1GROWTil RATE ANALYSIS OF TS ODIGA........................................... 73 ^
8.1 . I n trod ue t i on . . . . . . . . . .. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2- ' M e thod ol ogy.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Eval uation o f Voltage Change...................................................................... 74
~ 8.4 Bounding Growth Rate for Integrity Assessment ........................................ 82 8.5 : R e fere n ce s . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.0 . ODIGA ARC REPAIR LIMIT AND IMPLEMENTATION STRATEGY . 83 9.1 R epai r L i m i t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . 9.1.11 O ve rall A ppro ach .. .. . . . . . . . . . .. . .... . . . ... . .. .... . .. . . .. . .. ... .. .. . .. . .. .. . ... . . . . . . . . . . .. . . .. . .. . .. . . . . 9.1.2 : Voltage Threshold Val ue... ......... .......... ........... ............................................. 83 - 9.1.3 Adj ustments to Threshold Value .................................................................. 84 9.2 Implementation o f Criteria ........................ ........... .......... ... .. ...... . ... ........... . . .. 8 5 - 9.3 Summary.......................................................................................................86 Appendix A EC Acquisition and Analysis ....... .......................................................... A _- 1
' Appe ndix B M S L B Tran si ent .. . . . . . . . .. .. . . .. . . . . . . .. . . . . . . . . .. . . . .. . . . . .. . . .. .. . . ... . ..... . . ... . . . . .. . . . . . .
A ppend i x C . Ex cl usio n Zo ne .. . .. .. . . . .. . . .. .. .. . . .... . . . . .. .. . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . .. . .. . . . ... .
- BAW-10226 Rev.1 viii -
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LIST OF FIGURES Figure 1 Typical OTSG Tube Microstructure ............................................................ ..... 5 Figure 2 OTSG Longitudinal Section ......... ....................................................... .............. 6 Figure 3 Micrograph of UTS ODIG A ............................................................................ 12 Figure 4 Comparison of SEM Fractographic Data ......................................................... 13 Figure 5 LTS ODIG A Swelled Section .......................................................................... 14 Figure 6 S EM o f LTS O DIG A B urst Face ..................................................................... 15 Figure 7 Micrograph of Etched 1 st Span ODIGA .......... ............................................... 15 Figure 8 Micrograph of Polished 1 st Span ODIGA........................................................ 16 1;igure 9 SEM of LTS ODIG A Swelled Section........................... .................................. I 7 Figur c 10 Shallow ODIG A in 16th Span ............................................. ........................... 18
- Figure 111IF Bobbin [ ]6#..................................................,27 Figure 12 HF Bobbin [ ] _ _ _ - - . - _ _ 27 Figure 13 RPC [ ]6#............................................................28 Figure 14 RPC [ ]6#.......................................................28 6#
Figure 1511F Bobbin [ .................................................29 Figure 16 IIF Bobbin [ ],]#.............................. ..................29 Figure 17 RPC [ ]6#.........................................................30 Figure 18 RPC [ ]*#...........................................................30 Figure 19 [ ]'..............................32 Figure 20 [ l' . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Figure 21 [ ]*...............................33 Figure 22 [ ]'.............................33 Figure 23 Typical Lab Sample Microstructure........... .. ........... .................................... 37 Figure 24 Typical Optical Microscope View of Lab ODIGA Cross Section................. 38 Figure 25 Typical Field ODIG A Cross-Section ........................................................ .... 3 8 Figure 261IF Bobbin of Lab Sample [ ]*................................................................40 Figure 27 IIF Bobbin [ ]d .............................................40 Figure 28 RPC of Lab Sample [ ]d.............................................................................41
- Figure 29 RPC [ ]d ......................................................41 Figure 301IF Bobbin of Lab Sample [ ]d..................................................................42 Figure 3I IIF Bobbin [ ]d..........................................42 Figure 32 RPC of Lab Sample [ ]d........................................................................43 Figure 33 RPC [ ]d .......................................................43 Figure 34 0.510" Bobbi n Volt a ge vs %TW . . . . . . . . .. . .. . . . . . . . . . .. . . . . . . . . . . . . .. . . . . .. . .. . .. . . . . . .. . . . . . . . . . 4 4 Figure 35 0.510" Bobbin Voltage vs Axial Extent .......................................... ...... . ..... 45 Figure 36 0.510" Bobbin Voltage vs Circumferential Extent...................... ............. .. 45 Figure 37 [ ]'....................................56 Figure 38 [ ]'......................................57 Figure 39 ANO-1 SG A Voltage Rate of Change.................................................. ........ 81 Figure 40 ANO-1 SG B Voltage Rate of Change.......... ................................ ... .......... 81 Figure 41 Combined SG Voltage Rate of Change................................... ....................... 82 BAW-10226 Rev.1 ix
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, LIST OF TABLES L i i
-- Taole 1 OTSO Des gn I nformat on ... .. ...i .. .... . ... . . .... .. .... . . .. .. . .. . . . .. . .. .. . .... ... . . . .... . . . .. .. .... . . .. . .. . .. 7 Table 2 Pulled Tubes .With Volumetric ODIG A .............................................................. I 1 :
1 Table 3 Dimensiona! Analysis Summary ........................................ ............................... 19 . . Table 4 Volumetric ODIO A Database............................................................................. 21 Table 5 - Burst Testing of Volumetric Defects in a Tubesheet......................................... 48
' l Table 6 Normalization of 400 kilz Voltage to Mother-Standard ................................... _54 -
Table 7- Normalization of ANO 1 Pulled Tube OD10A................................................. 55 , Table 8 - Analysis Variability Study................................................................................. 59 Table 9 110t Leak Test Parameters ........................................................ .......................... 65 Table 10 . EDM Leak Test Specimens .._........................................................................... 6 7 Table 1 1 OTSG ODIG A Leak Rate Database ................................................................ 70 '
- Table 12 ANO-1 ODIG A Voltage Rate of Change ......................................................... 74 Table 13 ANO-1 SG A ODIG A Voltage Data ............................................................... 75 1 Table 14 ANO. I SO B ODIGA Voltage Data............... _................................................ 78 .
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- BAW-10226 Rev.1 --
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ACRONYMS AND AHHREVIATIONS ANO1 Arkansas Nuclear One- Unit 1 ARC alternate repair criteria BWOG B&W Owners Group CR-3 Crystal River-Unit 3 DB-1 D*vis Desse - Unit 1 DE destructive examination EC eddy-current FS free span (tube is not surrounded by a support structure) 11F high frequency, a type of bobbin coil probe llPFW high pressure feedwater heater IGA intergranular attack IGSCC intergranular stress corrosion cracking LPFW low pressure feedwater heater LTE lower tube end LTS lower tubesheet secondary face or lower tubesheet MSLB main steam line break MSR moisture separator /rcheater MR mid range, a type of bobbin coil probe NDE non-destructive examination NRC Nuclear Regulatory Commission OD outer diameter ODIGA outer diameter intergranular attack ONS-1 Oconee Nuclear Station- Unit 1 ONS-2 Oconee Nuclear Station- Unit 2 ONS 3 Oconee Nuclear Station - Unit 3 OTSG once through steam generator POL probability ofleakage RC rotating coil technology, such as RPC or Plus-Point RPC rotating pancake coil RSG recirculating steam generator SAM scanning auger microscopy SEM scanning electron microscopy SG steam generator SLB steam line break TMI-l Three Mile Island - Unit i TS tubesheet TSP tube support plate TW through-wall UTE upper tube end UTS upper tubesheet secondary face or upper tubesheet in table 4, UTS is ultimate tensile strength XPS x-ray photoelectro-spectroscopy YS yield strength BAW-10226 Rev.1 xi
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1.0 INTRODUCTION
1.1 Purpose The purpose of this document is to provide a technical justification to implement an alternate tube repair criteria for volumetric outer diameter intergranular attack (ODIGA)in the tubesheets of B&W Once Through Steam Generators (OTSGs). The justification considered the criteria and guidance contained in the NRC Generic Letter 95 05: Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by ODSCC, NRC Regulatory Guide 1.12) and NRC Draft Guide 1074. 1.2 Backpound Volumetric ODIGA is defined as three-dimensional corrosion at the grain boundaries which initiates from the outside of the tube. Volumetric ODIGA has no stress corrosion crack-like characteristics. Volumetric ODIGA has been found in a number of OTSG plants through tube pull examinations over the last several years. Due to better Er techniques, small amplitude ODIGA indications are being confirmed with RC and are being removed from service. Tube pull and laboratory induced ODIGA samples show that the volumetric ODIGA has little or no impact on the integrity of the tube and do not leak at these small unplitudes. Allowing tubes with volumetric ODIGA to remain in-service can be justified based on a combination of enhanced in-service inspection techniques and a repair limit based on eddy current response voltage. 1.3 Rere t Organization in order to establish the basis for an alternate repair criteria, the following items must be addressed:
- Flaw morphology must be established. This has been done for OTSG ODIGA based on tube pulls, and is summarized in sections 3 and 4.
- The efTect of ODIGA on the structural integrity of the tube must be established. This is summarized in section 5.
- The bobbin coil voltage response for ODIGA flaws in the OTSGs must be established. The EC guidelines for acquisition and analysis must also be established. These are summarized in section 6 and Appendix A .
BAW-10226 Rev.1 1
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1The probability _of leakage of the ODIGA flaw.in relation to a bobbin coil
- L voltage during a Main Steam Line Break (MSLB) must also be established. ,
' This is summarized in section 7 :- ,
[ e i in order to ensure that an' indication in a steam generator tube will not grow into _an indication that could possibly leak during an operating cycle, the . . _ growth rate of. ODIGA. in the TS must also be . established. : This -is
' summarized in section 8. -)
e - -In order to implement an A'tC, . inspection- guidelines, inspection scope,' > voltage repair limit, and exclusion zones for implementing the ARC must be
< established. - These are summarized in section 9 and Appendices A' and C.-
t r
^
iBAW-10226 Rev.1' , rvr, -- - - a < s- n ,-- , ,, ,
2.0 DESCRIPTION
OF OTSG There are currently seven operating nuclear power plants in the United States that use model 177FA OTSGs. They are Arkansas Nuclear One Unit 1, Crystal River Unit 3, Davis Besse Unit 1, Oconee Nuclear Station 1, Oconee Nuclear Station 2, Oconee Nuclear Station 3, and Three Mile Island Unit 1. The OTSGs at all these plants are nearly identical in design and function, and have similar tube material properties. 2.1 Functional Description The OTSG is a straight-tube, straight-shell, vertical, counter-flow, once-through heat exchanger with shell-side boiling. By nature of its design, the OTSG eliminates the need for steam separating equipment. In the OTSG, shown in Figure 2, primary fluid from the reactor enters through an inlet nozzle in the top head, flows dowa through the tubes, is collected in the bottom head and exits through two primary outlet nozzles. The feedwater enters through a series of spray nozzles near the top of the annular feedwater heating chamber. Here the feedwater is heated to saturation temperature by direct contact with high quality or slightly superheated " bleed" steam. The resulting saturated feedwater enters the tube bundle through ports near the bottom of the tube bundle. Nucleate boiling starts immediately upon contact wit! the hot tubes. Steam quality increases as the secondary fluid flows upward between the tubes in counterflow to the primary fluid inside the tubes. The departure from nucleate boiling (DNB) occurs at about the 25-foot level at design conditions. The mode of heat transfer then changes from nucleate to film boiling. Steam quality continues to increase but at a slower rate. After 100% quality is reached, the steam becomes superheated, leave; the tube bundle at the upper tubesheet, flows down the steam annulus, and exP,s through two steam outlet nozzles. All B&W designed plants opt rate at similar conditions. Because the plants have similar reactor coolant system flow rates, the core AT's are similar and thus the values for Tw and Tcou are similar. [
]* These values can vary due to T., control and tube plugging. (Tube plugging reduces reactor coolant system flow rates and increases the AT across the core.)
Outlet steam temperatures can vary from the minimum design value of [
]* to about [ ]* depending on steam generator design differences, fouling, and tube plugging. All plants have, to date, performed well in excess of the [ ]*. Typical steam temperatures are between [ ]*and
[ ]*. BAW-10226 Rev.1 3
2.2 Design Information The units weigh approximately 570 tons and have an outer diameter of 12-1/2 feet and overall height of 73 feet. Table 1 contains a summvy of the OTSG design data. Each steam generator has more than 15,000 triangularly spaced alloy 600 tubes. These tubes are 5/8 in. OD x 0.037 in, nominal wall x Si d. long. They are partially roll expanded (1 in, nominal) and seal welded in the upper and lower tubesheets. The use of straight tube results in almost pure counterflow with resulting improved secondary flow distribution and primary-to-secondary temperature differentials. This design also has the benefit of a compressive loading on the tubes during normal operating conditions. This is mainly due to the fact that the alloy 600 tubes have a thermal coefficient of expansion slightly greater than that af the carbon steel shdl. This compressive load tends to inhibit the initiation and propagation of some stress related damage mechanisms. Proper lateral spacing of the tubes is maintained b i 15 tube support plates. They are fabricated from 1 1/2 in thick carbon steel plate, drilled and broached to provide surface contact and support along three axes for each tube at each tube support plate. An excep: ion is the 15 TSP periphery rows, which are not s broache.l. The support plates are non unifomily spaced axially to prevent resonant vibrations along the tube length, thus providing the highest possible damping factor. 2.3 Tube Material Properties The OTSG tube material in all seven operating plants is alloy 600 (ASTM SB163). The raw materials were both melted into the alloy 600 ingots and fabricated into hollow rounds by B&W Tubular Products Division (TPD) for the OTSG tubing. The tube fmishing processes (tube drawing, etc.) were performed by TPD and two outside vendors. The tube material was later thermally treated at [ ]' for a minimum of [ ]* hours during the full furnace stress relief of the completed steam generator. As a result, the installed tubes are both sensitized and stress relieved, which provides improved resistance to caustic stress corrosion cracking but makes it more susceptible to intergranular attack caused by reduced sulfur species. The microstructure of sensitizea tubes exhibit a large number of fmc intergranular carbide particics (see Figure 1). Average ASTM grain size for a typical OTSG tube varies from [ ]'to[ ]*. BAW-10226 Rev.1 4
~ . _ . . _ _ _ ._ _ - _ . . . , . - . _ - . - -. - _ _ . _ , - . - ~ . _ . _ _ . _ ,
a Figure 1 Typical OTSG Tube Microstructure D' ._ I i.
. i 1
2.4 Conclusions ' ! ~All currently operating U.S. plants with OTSGs have Babcock & Wilcox model , 177FA steam generators. . These OTSGs were all fabricated in the same time " period, utilizing the same general-design and materials. Variability in tube material properties is limited due to the sole source melting of the alloy 600, consistent fabrication specifications, and consistent thermal treatments. These plants also operate at similar conditions. Thus, all'once-through stca generators [ can be considered generically with regard to design, function, and materials, 1 3 i 1
,s.
(
+
N ' BAW-10226 Rev.1 ^ - S' yt ,. - -
- .~-.m . . , , , . , , . . . - . . ..,s m. . . -, . _, , ,
l Figu 2 OTSO Longitudinal Section I
~ O' l i
?
BAW-10226 Rev.1 6
Table 1 OTSG Design Information U* i BAW-10226 Rev.I 7
3.0 ASSESSMENT OF ODIGA While there are various types ofintergranular corrosion, only volumetric ODIGA is addressed by this ARC. To establish whether or not this damage mechanism is generic to all OTSGs, the secondary side chemistry controls at all the OTSG plants and the results of destructive and non-destructive examinations of pulled tubes with volumetric ODIGA were compared. These comparisons show that all the plants operate to the same secondary side chemistry specifications, and the volumetric ODIGA is similar in morphology and EC response. ?.1 Background Intergranular corrosion (IGC) in the form of intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) has been experienced on the secondary side of PWR steam generator tubes. IGA is defined as three-dimensional corrosion at the grain boundaries.1GA can occur in isolated patches or at multiple initiation sites encompassing a given area. Typically, the width of the corrosion will be equal to or greater than the deptn of the corrosion when classified as 1GA. In some cases, localized fingers of grain boundary attack may extend below a layer of general !GA. These fingers are sometimes referred to as intergranular penetrations (IGP). IGSCC is defined as two-dimensional corrosion of grain boundaries that is strongly stress dependent. IGSCC is typically observed to be axially-oriented but may also be circumferentially-oriented or a combination of the two. The morphchgy of the IGSCC degradation produces cddy current signal characteristics which allow it to be distinguishable from volumetric OD IGA. The presence of preferential crack orientations in IGSCC is detected through the use of a three-coil rotating probe (see section 3.4.2). IGC or the secondary side has been found in a great number of PWR steam generators. IGC in RSGs has been strongly correlated with the presence of as-built crevices and crevices formed by the deposition of sludge, such as on top of tubesheets. This is attributed to the fact that the mill anneated alloy 600 tubing in RSGs has been found to oc highly susceptible to caustic-induced IGSCC. As stated in action 2.3, OTSG tubing is sensitized alloy 600, which has improved resistance to caustic attack, but increased susceptibility to intergranular attack caused by reduced sulfur species. Based on both laboratory and field data, intergranular corrosion has been found to occur in a variety of contaminant environments. At operating PWR plants these include *: high concentrations of caustic solutions; reduced sulfur species in oxidizing environments, acidic environments at layup temperatures; acidic sulfur species from thermal decomposition of cation exchange resins and organic impurities that pass through makeug)and condensate demineralizers; and lead and its compounds. In the laboratory , IGC has been produced in alloy 600 in environments containing: those conditions under which operating plants BAW-10226 Rev.1 8
develcped IGC; highly concentrated salt solutions at neutul or near neutral pH; and thermal decomoosition products of neutral clays and colloids. 3.2 Secondary Side Chemistry Control Limiting the amount of contaminants introduced into the secondary side of the SG is important in the management of ODIGA. The following sections first compare the RSG and OTSG chemistry control features, and then give a history of the ' OTSG chemistry control programs. 3.2.1 RSG and OTSG Operating Features Affecting Chemistry Control A great deal of data has been accumulated on IG A and IGSCC of alloy 600 in RSGs.(" In addition to tube material differences between RSGs (mill annealed alloy 600) and OTSGs (sensitized alloy 600), significant operating differences exist which affect steam generator water chemistry control and the corrosion susceptibility of the alloy 600 tubes, in an RSG during power operation, saturated steam is produced from the boiling that occurs in a recirculating pool ofliquid. Water soluble impurities entering the RSG preferentially remain in the liquid phase due to the steam-liquid partitioning, and blowdown of the liquid phase is used to control the steam generator bulk water chemistry. Thus, some portion of the contaminants introduced with the feedwater are removed after entering the steam generator. An OTSG operates much like an RSG during limited periods of operation at less than 15 percent power during plant startups. Water soluble impurities will concentrate in the OTSG bulk water due to pool boiling. Bulk water quality is
-maintained during these periods by blowdown and/or by controlling feedwater purity with condensate polishers.
Impurities, such as sodium chtnric'.e and sodium hydroxide, entering the OTSG are soluble in the superheated steam at operating conditions *, Most of these impurities are transported through the OTSG with the superheated steam and are removed from the system by the condensate polishers. This process provides a mechanism (as blowdown demineralizers do in RSG systems) for the removal of chemical impurities from the system. 3.2.2~ OTSG Chemistry Control The experience gained from the well-established fossil fired once-through B&W boilers provided the basis for the OTSO secondary water chemistry operating specifications. Since blowdown is not used in either the fossil fired or nuclear once-through boilers during normal power operation, high-purity feedwater is required and is the control point for OTSG water chemistry. That is, the presence of contaminants in the OTSG is controlled prior to entry into the boiler, ratner BAW-10226 Rev.1 9
than after, as is the case with_ RSGs. ac no blowdown is employed during power operation, the OTSG secondary water chemistry specifications include an all volatile (zero solids) chemical treatment program and full flow condensate polishing. All OTSO plants have either full flow powdered resin or deep bed condensate demineralizers. Full flow condensate polishing was specified to ensure feedwater quality and facilitate pre-boiler cycle cleanup during startup, prior to introducing feedwater to the OTSGs. All OTSG plants have been operated using the same B&W secondary water chemistry specifications provided prior to the startup of Oconee Unit-1, the first OTSG plant. Chemistry specifications for all plant conditions were specified.
. including hot functional testing, startup, normal operation, shutdown, and layup.
Uniform and evolutionary improvements have been made to these specifications, 04) including endorsement of the EPRI Secondary Water Chemistry Guidelines . All OTSG plants were initially brought into service using ammonia for pH control and hydrazine for oxygen scavenging. The OTSG plants have historically employed either high feedwater pil (9.4-9.6) for an all-ferrous BOP, or a lower operating feedwater pH (8.9 9.1) due to the presence of copper in the BOP of some plants. Beginning in 1988, in order to lower the feedwater iron transport rate, the OTe'l plants began using alternative amines, such as morpholine, rather than ammonia. 3.2.3 Sumn ary of Secondary Chemistry Evaluations OTSG plants have always operated to consistent secondary water chemistry specifications which provide high-purity feedwater to limit the presence of contaminants in the OTSGs. Throughout the operating histories of the OTSGs, unifomi and evolutionary improvements have been made to these specifications and guidelines to further improve feedwater quality. Water soluble impurities that are transported through the secondary system are removed by the use of condensate polishers. These efforts result in the limitation of the amount of contaminants deposited in the OTSO, which aide all the OTSG plants in the management of ODIGA. BAW-10226 Rev.1 10
l L3.3 - - Morphology of Pulled Tubes'. j As stated in section 3.1, there are two general forms of IGC: IGSCC, which is- l ! crack-like, and IGA, which is volumetric. ; The marphology being addressed _in this report is volumetric outer diameter IGA. This section presents a sumniary of
~
the critical characteristics of ODIGA, based on the destructive examination results of tube samples removed from operating OTSGs.
~ The current _ volumetric ODIGA database inchdes- 162 patches in 17 tubes-
- removed from'4 of the 7 operating plants with 013Gs. These tubes and the plants from which they were removed are listed in Table 2. Each of these tubes contain one or more occurrences of volumetric ODIGA which were. confirmed -by
- destructive examination. Significant results. from these examinations that are-
. pertinent to the -mc phology of volumetric ODIGA in OTSGs are discussed and , illustrated in the following sections for e&ch of the plants listed in Table 2. Table 2 Pulled Tubes With Volumetric ODIGA
- i. ge 1 ,
I 5. f 4 I r
- r, BAW-10226 Rev.1 11
3.3.1 [ J'
., l I l
]*
Figure 3 Micrograph of UTS ODIG A [je.d 75X, reduced 20% for report [ BAW-10226 Rev.1 - 12
]*
Figure 4 Comparison of SEM Fractographic Data [je.d d BAW-10226 Rev.1 13
3.3X [ . ]* I
]'
Figure 5 LTS ODIGA Svelled Section ()c,d 36.7X, reduced 20% for report BAW-10226 Rev.1- 14
Figure 6 SEM of LTS ODIGA llurst Face l}' I l' Figure 7 Micrograph of Etched 1st Spaa ODiGA ll' 200X, reduced 5% for report ilAW-10226 Rev.1 15 w-
l
)
Figurc N Micrograph ofl'olished 1st Span ODIGA []' 100X 3.3.3 [ ]' I
]*
BAW 10226 Rev.1 16
Figure 9 SEM of IXS ODIGA Swelled Section []' 3.3,4 [ ]* I
't j'
BAW-10226 Rev.1 17
I 4 i 3 Figure 10 Shallow ODIGA la 16th Spaa j i (f i i l 1 4 l I i i i 3.3.5 Plant to-Plant Comparison and Morphology Summary- ; A total of 17 OTSO tubes have been removed from service and had volumetric ODIGA confirmed as a damage mechanism. LOA has been found in the~ upper and lower tubesheet regions, as well as the 1"(bottom) span ,14* span,15* span, - i and 16* (top) spans. A total of 162 OD volumetric 10A patches have been ! confirme :d by destructive examination. Table 4 itemizes the available dimensional and mechanical property data for each of these patches, , ini order to determine if IOA can be treated- generically in the ARC, the morphology of LOA pulled from all plants was compared. The results of this - ! comparison are presented in the following paragraphs. l i Characteristles of Decradation- i
~
-{- i BAW-10226 Rey,1l 18 s !
s- # , r,- + y . - ,-+m , - - + c ,' + -
.m v , -ww .--w* eaww w.- %m *-we,u5,~.-..----,.---v, .5--e- * , + , = - - = - - - . .- -e,- = --
}'
Shape of Degradation I l' Tahic 3 Dimensional Analysis Summary [)hc Chemistry I l' 13AW 10226 Rev.1 19
? ', Conclusions on Flaw Morphology IL s A on the results of laboratory axaminations, the characteristics of the n .. .etrie ODIGA rnorphology are essentially the same for all the plants from
, winch tubes were pulled. [
]" It is therefore concluded that volumetric 10A can be treated generically in the application of an ARC in OTSOs from which tubes have been pulled. plants which have not pulled tubes will need to do so to confinn the same ODIGA morphology. -
l l l l l l IIAW 10226 Rev.l . 20 l
i i
]
i l l i i ta9 h a - 0 N , a 1 O 0 O U .g a v E s C w .I a M h 9 D x e c0
Tabic 4 Volumetrie ODIGA Database (Cont.) lf L BAW-10226 Rev.1 22
y. Table 4 volumetric ODIGA Databaw (Cont.) If 4-BAW-10226 Rev.1 23
Table 4 Volumetric ODIGA Database (Cont.) If i BAW-10226 Rev.1 24
- . _ . = _ - _ _ _ _ _ _ _ . _ _ - _ _-_ - --_-____-
Table 4 Volumetric ODIGA Database (Cont.) [T BAW-10226 Rev.1 25 t-
l l 3.4 EC of Pulled Tubes An evaluation of PC data on pulled tubes was conducted to detennine the EC characteristics of the volumetric ODIGA morphology. The results of this evaluation are presented in the following paragraphs. Also presented are examples of the EC characteristics ofIOSCC. This evaluation demonstrates that IOSCC, which is enck like and therefore not addressed by this ARC, can be readily differentiated from volumetric IOA during field EC examinations, j 3.4.1 ODIGA Reliable detection of volumetric ODIGA by bobbin coil examination has been demonstrated by EC performance validation testing using pulled tube data. The ODIGA is typically characteri.md by a low voltage bobbin signal. Since the ODIGA is localized in a small area, it is typically confirmed to be volumetric by a rotating coil examination. The EC responsu to more than 50 patches of volumetric ODIGA from several different OTSO plant tube pull samples were evaluated, and the typical respor.ses are compared below. The purpose of this comparison is to demonstrate that the eddy current characteristics are similar. It is not the intent of this comparison to match up patches with exactly the same dimensions. Differences in the patch size can result in differences in voltage amplitude, which can be seen in the figures which follow. It is also noted that some of the MRPC terrain plots contain multiple indications. The indication ofinterest is centered on the terrain plot and on the strip chart. Plant to Plant EC Siunal Comparison Figure 11 and Figure 12 show the bobbin coil indication data for two representative ODIGA patches from different plants and different locations within the OTSO. [
)b.c BAW 10226 Rev.1 26 v- - - y4 w t-i m v--, p>r--ge- y-y
-wei-es?ew-fzr------r7e----- tiq--~~--e -'-mi.-- v- --- -- -w -m e-%.q-----w---rm-m -- 2r w e- -wwe------m +rmr-w em---
Figure 1I IIF Ilotiliin l lb# []b" Figure 12 IIF Ilol>liin l lbd []b# 11AW 10226 Rev.1 27
Figure 13 and Figure 14 show the MRPC pancake coil data for the patches in the above plots. [ s
)he Figure 13 RPC l l6"
[)de Figure 14 RPC l lhe [jbs llAW 10226 Rev.1 28
1 t i Figure 15 and Figure 16 show additional e>:amples of pulled tube IGA bobbin coil cddy ; current responses [ l js t 6 Figure 15 HF Bobbin l 1# ) ll'# l i h i I 1 i i ! l- l t i I
- I t
1 l t T P 4 l Figure 16 HF Bohhin l ]6# 4)be i I 4 l l P t
. HAW-10226 Rev,1 29
-i l
---w- ....cn. ._. , 3, ,,---g. , y m,,--,-+,vw,- , , ..-.wr -,e--. . ...<33.w,-e..,--,.,m.w,,tc.,,,,,- .e,%,, .. rv,-
.. . . . . _ _ - . . . . . . ~ . . - . - . . . - - . . _ - _ . - - ~ - . . .
l 1 i i Figure 17 and Figure 18 show the rotating pancake coil _ data on the same two. l patches from[ p ,
.]6#
Figure 17 RPC l l6d t {}'# { i i e f f i L L 6 r t t s
?
Figure IN RPC [ l6d ; i e I i
- j. . ' ,
l
)
k L I j-i 9 i bL - L 30;. ci 2 BAW-10226 Rev.I1 :1
+ J
.i uI
.- . ..- ..,. . .~ .. -.- .,. . ....,. . . - , ,
Sitnunen The eddy current responses of ODIGA from tubes pulled from different plants and locations within the OTSO are very similar. [ jb.e 3.4.2 Characterization of Crack Like vs Volumetric Morphologies
'ihe application of an Al(C for volumetric OD10A requires that the lic technique being used is capable of differentiating volumetric degradation from erack like degradation. The morphology of the 10 SCC degradation produces cddy current signal characteristics which allow it to be clearly distinguished from volumetric ODIOA. (
Y 1 i e t i DAW 10226 Rev.1 31 gr:-.
i I Y Figure 19 [ j' 0' Figure 20 [ j' b.e i l l l I 1 BAW 10226 Rev.1 32
Figure 21 and Figure 22 show [ l' Figure 21 l l' [jb.e Figure 22 [ ]' gjd BAW 10226 Rev 1 33
l l 3.4.3 Summary of EC Response Relative to Flaw Morphology
%e EC responses from volumetric ODIGA at different plants and locations within the OTSO are similar. This supports the generic EC characterization of l volumetric ODIGA for this ARC. Additionally, ODIG A is clearly distinguishable from intergraaular stress corrosion cracking through the use of RC examinations, which make use of directionally-oriented coils.
3.5 Sumtnary and Conclusions, OTSO OD10A Flaw Morphology 1hc morphology of OD volumetric IGA has been evaluated in detail in order to characterize this mode of degradation in operating OTSOs. This evaluation had two goals. The Erst goal was to determine if the IOA is similar from plant to plant and location to location in the OTSGs, which determines whether an ARC can be developed gnetically for all plants and locations. The second goal was to determine if available EC technology can ditTerentiate between volumetric IOA and 10 SCC; m that tM ARC could be applied in the field without inadvertently aptfit irg; r.vt !OSCC. In order to meet the first goal, a review of available deu on the occurrence of ODIGA !n OTSGs was conducted. This included an evaluation of the laboratory exam results of all tubes removed from OTSGs with confinned volumetric 10A, including a comparison of the morphology at different plants and locations within the 5,tcam generators. The ability of EC to differentiate between volumetric 10/. and crack like morphologies w.v investigated by comparing the EC response for known samples of volumetric IGA and axial IGSCC from OTSG tube pull samples. This evaluation included indications from different plants and locations. The following conclusions were drawn from these evaluations:
- 1. The morphology of OD10A in OTSGs is the same in all significant aspects -
regardless of location within the OTSO - for all the plants evaluated. Any minor variations in morphology that were identified can be accounted for in a generic ARC.
- 2. Rotating coil EC technology can diffe.cntiate between a volumetric patch of LOA and IOSCC, BAW 10226 Rev,1 34
3.6 References (1) EPRI Steam Generator Reference Book, Revision 1, December 1994. (2) Hell, M.J., et al, " Solids Behavior in Once-Through Nuclear Steam Systems", Presented to the American Power Conference, Chicago, IL, ; April 1977. (3) PWR Secondary Water Chemistry Guidelines, Special Report NP 2704 SR, October 1982, Electric Power Research Institute, Paio Alto, CA. 1 1 (4) EPRI NP 5056 SR, "PWR Secondary Water Chemistry Guidelines", Revision 1, March 1987, Electric Power Research Institute, Palo Alto, CA. (5) EPRI NP 6239,"PWR Secondary Water Chemistry Guidelinesl Revision 2, December 1988, Electric Power Research Institute, Palo Alto, CA. (6) EPRI NP 102134, "PWR Secondary Water Chemistry Guidelines", Revision 3, May 1993. Electric Power Research Institute, Palo Alto, CA. (7) EPRI NP 102134, "PWR Secondary Water Chemistry Guidelines", Revision 4, November 1996, Electric Power Research Institute, Palo Alto, CA. (8) K.R. Redmond and P.A. Sherbume, " Examination of Crystal River 3 Steam Generator Tube Sections", EPRI Report TR 103756, April 1994. (9) L.J. Sykes and P.A. Sherburne, " Analysis of Steam Generator Tubing from Crystal River Unit 3", EPRI Report TR 106483, April 1996. (10) L.J. Sykes and P.A. Sherburne, " Analysis of Steam Generator Tubing . from Oconee 1 Nuclear Station", EPRI Report TR 106484, April 1996. BAW-10226 Rev.l. 35
4.0 1,AllORATOlW ODIGA FOlt ARC The ability of laboratory IGA to simulate in-generator IGA was evaluated by comparing the laboratory IGA to similarly sized field flaws. This was accomplished by destructively examining laboratory IGA specimens and comparing their morphology to the significant features of the field IGA patches identified in section 3.3 of this report. The EC responsv was evaluated by comparing critical parameters of the laboratory IGA to the same parameters for field IGA from pulled tubes (section 3.4). The results indicate that the laboratory IG A is the same morphology and exhibits the same EC response. 4.1 Introduction Although many volumetric GDIGA patches have been removed from OTSGs, all have been too small to have any significant impact on the structural integrity of the tube, in addition, none of the helium leak tested field IGA has leaked. The lack of large IGA patches that challenge structural integrity, or that even leak, make it difficult to develop the structural and leakage correlations that are necessary in the development of an ARC. For this reason, laboratory genemted ODIGA must be utilized to supplement the field IGA database. in order to use tl e laboratory IGA as a supplement for the ARC, it mast be demonstrated that the laboratory IGA is fu'ly representative of the field IGA. Two basic sets of crderia must be satisfied. First, the physical morphology of the laboratory IGA must be the same as the morphology of field IGA. This ensures that the impact on structunil and leakage integrity due to a laboratory produced flaw is the same as the impact for a similar size field flaw. Second, the EC response to a laboratory IGA patch must be the same as that for a similar size field patch. This ensures that any correlations developed that depend on the EC response of the degraded tube will be applicable to a field examination of real IGA indications. 4.2 Key parameters The following acceptance criteria were established to evaluate the acceptability of laboratory samples to supplement the field ODIGA database: l IIAW-10226 Rev.1 36 l
jb.t.d 4.3 1,aboratory Sample Fabrication The tubing used for the laboratory samples was taken from a production heat and Tliis tubing was subjected to a vacuum furnace neat lot number treatment of[ of OTSO ] tubing; for to[ fully sensitize the material. Figure
]d hours 23 and Figure i present the microstructure of a typical laboratory sample and that of a tube removed from an operating OTSO, respectively. Note that both tube samples exhibit a large number ofintergranular carbides. Average ASTM grain size for the laboratoiy samples was measured as [ ]d; the average grain size for a typical OTSO tube varies from ASTM [ ]'.
Prior to submittal to the laboratory, the tube samples were inspected by eddy current techniques for baseline information and for the climination of tube specimens with either pre existing flaws or exhibiting " noisy" eddy current signals. Figure 23 Typleal1,ab Sample Microstructure 11* 100X, reduced 35% for this repod 4.4 Itesults of Laboratory Sample Evaluation Program , The laboratory induced volumetric ODICA samples were produced [
]' Following EC and destructive examination, the laboratory samples were then compared to pulled tube ODIGA based on the acceptance criteria listed in section 4.2. The follow'ng information summarizes the evaluation of the laboratory samples.
4.4.1 Destructive Examination Results The laboratory IGA was destructively examined and compared with field LOA on the basis of metallographic sections. Figure 24 shows a typical metallographic section of a laboratory flaw, which may be compared to a representative sample 13 AW-10226 Rev.1 37
l from a pulled tube presented in Figure 25. Evaluation of the laboratory samples showed [ t jb.d i Figure 24 Typical Optical Microscope View of Lab ODIGA Cross Section [l i x I
?
25X ! Figure 25 Typical Field ODIGA Cross-Section ; Il* i 1 i i 75X l l i i BAW 10226 Rev.1 38: t I y, y.. ,< , p -e ..w--, r-,,.,-. , ..r.. , w,-,, . _ _ , s.-,_ ,,. ..-..r. - ..m.,.. . _'-.
3 4.4.2 Eddy Current Evaluation Results The acceptability of the laboratory samples relative to EC was evaluated by comparing the signal response of the laboratory samples to the response for similar field IOA from pulled tube samples. The acceptance criteria were defined ! as follows: l , )b,e Comparison of Sicnal Characteristics , [ l' t BAW-10226 Rev.1 39 ,
Figure 26 IIF llobbin of1,ab Sample [ f Il' Figure 27 IIF llobbin l jd d Il 13AW-10226 Rev.1 40
jb.e Figure 28 RPC of Lab Sample [ ]8 (I' Figure 29 RPC [ jd ll' - BAW 10226 Rev,1 41
k i The next set of figures show a response comparison for laboratory and field LOA ~
~
widi less severe degradation Figure 30 and Figure 31 show the high frequency bobbin coil response for a laboratory sample and a tube pull sample, respectively. . Figure 30 HF Bobbin of Lab Sample [ jd - D' ,. t i I 1 i ' Figure 31 If F flobbin [ ld i []d 1 BAW 10226 Rev.1 -42L l p l' j g. - _- - - - f :
-. .2... ._ . _ . . . , _ . . . . _ _ . _ _ , , _ _ _ _,
l
- Figure 32 and Figure'33 show the MRPC responses for the same IGA patches.
! Again, the signal response of the laboratory sample is similar to the response of--
the comparabic field IGA patch. i Figure 32 RPC of Lab Sample [- ]d [jd Figure 33 RPC [ ]d []d e BAW-10226'Rev.l! 43 1
- - __ - . _ - _ _ - _ _ _ - - - ------.__--__-c____'---_----.-_--_--_____n.-_-._.
Compa.rison of EC and DE Parameters Although the initial laboratory samples were examined with several different probe types, the high frequency (IIF) bobbin coil eddy current probe responses and destructive examination results are compared in the following plots to show that the signal voltages are consistent with the IGA defects found in operating OTSGs. This probe is utilized because the bulk of the historical field data is based on the HF probe. It is not the intent of these plots to establish correlations of eddy current voltage to depth, axial extent or circumferential extent, but to demonstrate that the laboratory samples are representative of actual field IGA. Figure 34 0.510"11obbin Voltage vs %TW U' BAW-10226 Rev.1 44
. . - , .....~ . . . . , - . - - - . . -.. _ . - ..-.... -- _- ~~- -- . . _ . .
?
-1 4 -L- _ ?
J
- Figure 35 0.510" Bobbin Voltage u 3 sial Extent -
.. '[]d _
- 1 a
. I 4 ,
! i 1
4 . 4
?
.e i
e 4 e J e i t i-
- Figure 36 0.510" Bobbin Voltage vs Circumferential Extent i
-d 3
a 4 [j-1 f 2 1 t( . . J
\
i .- w I 4 i
- . ' m ^
i M j - ,_. , , . F-
, BAW-10226 Rev.l . i45
.- -r a ^2 k: .
,+~.,mlwev,,.n
&. , ,r,- m.. ,ee, ew,,- e se < . e n ,,-,-.., w s, m ,. a
These plots show that the bobbin signal amplitude responses of the laboratory IGA specimens are representative of the actual field ODIGA. 4.5 Summary and Conclusions, Laboratory Sample Evaluation Laboratory samples with simulated IGA were fabricated and evaluated to determine how closely they approximated service-induced IGA. The evaluation was based on a comparison of physical flaw morphology and the EC response of the flaws. The results of the evaluation indicated that the physical morphology of the laboratory IGA was the same as field IGA, exhibiting the same shape, the same appearance of grain boundary attack, and the absence of significant detrimental characteristics such as pitting and destruction of the grains. The evaluation of EC response was performed to demonstrate that the signal characteristics of the laboratory samples were similar to the typical EC responses to field volumetric ODIGA. The evaluation found that the laboratory IGA produced EC responses that were representative of similar field IGA. As a result of the above findings it was concluded that the laboratory IGA is fully representative of service induced volumetric ODIGA. The laboratory flaws can therefore be used to supplement the pulled tube ODIGA database for the l development of the ARC. BAW-10226 Rev.1- 46
5.0 STRUCTURAL EVALUATION OF TUBESIIEET ODIGA To evaluate the structural integrity of volumetric ODIGA in the tubesheet agions of OTSGs, burst rupture, tensile rupture, and fatigue failure modes were evaluated. The presence of the tubesheet precludes burst rupture of the IGA. Testing of axial loads up to [1.718 times MSLB load (at MSLB pressure and temperature) showed no indications of any tensile rupture concerns. Fatigue is addressed through preventive sleeving, the application of the exclusion zone, and examination of all ARC indications at each scheduled inspection. In conclusion, there are no structural concems with regard to volumetric ODIGA in the voltage range tested [ ]d 5.1 Introduction Structural evaluations were performed to determine the impact of bounding design bases conditions on tubes containing volumetric ODIGA. The structural evaluations for volumetric ODIGA contained within the tubesheet regions of the OTSG include the following:
- 1. Identify any exclusion zones for ODIGA indications in areas adjacent to the tubesheet secondary face, where moments are imposed on the tubes during MSLB conditions, but not during testing.
- 2. Demonstrate that the burst rupture of volumetric ODIGA is precluded by the limited tube-to-tubesheet diametral clearance.
- 3. Determine if failure modes other than tube burst rupture, (i.e. tensile rupture), define a more conservative structural limit for the ARC.
5.2 Tubesheet interface ARC Exclusion Zone Bending moments exist at both tubesheet faces due to cross-flow loads during normal and faulted conditions. The limiting bending moment exists at the upper tubesheet secondary face (UTS) during a MSLB cvent, when the secondary side steam rapidly accelerates up through the tube bundle and then radially out of the SG through the steam outlet nozzles due to the pressure differential caused by the downstream break. While these lateral loads exist for only the first few seconds of the MSLB transient, they could potentially change the condition of the volumetric ODIGA defect that is exposed to the high primary-to-secondary pressure differential and axial load later in the transient. A program was therefore undertaken to define the relationship between the lateral load, the bending moment, and the position of the defect within the tubesheet, for the purpose of defining an exclusion zone outside of which the cross-flow loads are determined to have a negligible effect on the condition of the volumetric ODIGA defect. Based upon the analyses presented in Appendix C, the exclusion zone was determined to be [ ]d This ODIGA exclusion zone length will be expanded to encompass [
]d to account for eddy current uncertainty.
BAW-10226 Rev.1 47
5.3 Burst Rupture Evaluation Experiments have been performed to determine the burst pressures for tubes having outer diameter initiated axial cracks that are contained within a suppon with relatively small annular distances.m The results from these experiments show that flawed tube burst below the burst pressure for an unflawed tube is precluded by the constraint of the tube radial displacement when the cracked section of the tube remains within the tubesheet and the diametral gap is less than approximately 0.030". The bounding tube-to-tubesheet diametral difference for all OTSGs is computed by assuming the minimum tube OD (0.625") and the maximum tubesheet bore ID (0.646"), resulting in a diametral gap of 0.021" Based upon the results of the EPRI testing discussed above, this gap is not sufficient to burst an axially cracked tube within the tubesheet. FTl performed burst testing of machined 100%TW defects confined within a tubesheet to determine if this assumption is also applicable to volumetric defects. [ d l Table 5 llurst Testing of Volumetric Defects in a Tubesheet d ll 48 l BAW-10226 Rev.1
[
]d These test results demonstrate that volumetric ODIGA which is located within the tubesheet is precluded from burst. This ARC ensures that the indications are located within the tubesheet by virtue of the exclusion zone discussed in section 5.2. This climinates the need to determine a volumetric ODIGA structural limit based on burst pressure.
Although the tubesheet precludes the IGA from burst rupture, freespan burst pressure testing was conducted on the laboratory samples. The freespan burst pressures ranged from [ ]d psi, compared with an average burst pressure of [ ]d psi for unflawed samples. The burst pressures for all the laboratory samples are directly comparable because all the samples were made from the same heat of material. The results show that the lowest burst pressure is still within [ ]d of the unflawed burst pressure if the tubesheet effect isn't taken into account. 5.4 Tensile Rupture Evaluation As discussed in section 5.3, the presence of the tubesheet precludes the volumetric ODIGA from burst rupture. This results in the structural integrity being detemlined by the tensile rupture load. As discussed in Appendix B, the OTSG tubes are subjected to tensile loads during a MSLB due mainly to tube-to shell temperature differentials. A total of [ ]d ODIGA samples with a maximum voltage of [ ]d were tested at MSLB temperature and pressure. While the MSLB load is [ ]d LB, the testing resulted in no leakage or tensile rupture at the maximum tested load of[ ]d It is therefore expected that IGA indications with voltages in this range will not have a tensile rupture concern. 5.5 - Fatigue Evaluation Fatigue loading on OTSG tubes can be classified as either high-cycle or low cycle. Tube degradation due to high cycle fatigue has been observed in OTSGs at the 15th (uppermost) TSP and at the secondary face of the upper tubesheet. The resulting flaw morphology is a circumferential fatigue crack which propagates
. rapidly around the tube once initiated. The tubes affected are located adjacent to BAW-10226 Rev.1 49
the open tube lane, where secondary side cross flow is high. This damage
- mechanism was first identified in the late 1970's, and confirmed through examinations of tube pull samples from the ONS plants, it was concluded that the flaws were initiated at sites of localized coticsion or wear, and then were propagated into a fatigue crack by flow induced vibration associated with the high cross flow. ,
liigh cycle fatigue has been addressed in OTSGs by preventively sleeving the susceptible tubes. The lack of tubt ieaks attributed to fatigue in recent years supports the adequacy of the defined sleeving zone in bounding the susceptible area. The installed sleeves span the entire upper tubesheet and top span of the generator, so the ARC will not be applied to the susceptible area of these tubes, in addition, excluding { ]' from consideration also precludes high cycle fatigue from being a concern in other tubes to which the ARC can be applied. Addressing the effects of high cycle fatigue in the ARC is therefore not necessary. Fatigue due to low cycle loading results primarily from mechanical, thennal, and pressure cycling during normal plant operation. If flaws were to propagate due to low cycle fatigue, this would be evident as a change in the EC response of the flaw from one cycle to the next. Therefore any historical effects of low cycle fatigue on tubesheet OD IGA are included in the growth rate analysis discussed in section 6. Since the growth rate will be regularly monitored during implementation of the ARC, and flaws will be repaired prior to becoming a leakage or structural concern, a separate repair limit for low cycle fatigue is not necessary. 5.6 Summary of Structural Evaluations of Tubes Affected with ODIGA An analysis of bending moments was performed which established an exclusion zone of[ ]d. This was conservatively increased to [ ]' to account for eddy current positioning uncertainty. Testing of 100%TW machined holes with diameters up to [ ] demonstrated that the burst rupture of volumetric IGA contained within the tubesheet is not a concern. Large tensile loads applied during leak testing demonstrate the structural integrity of the IGA in terms of axial loads and EC inspection of the indications each refueling outage ensure that the integrity is maintained. The volumetric ODIGA does not, therefore, pose a structural threat to burst or tensile rupture under the postulated MSLB conditions. 5.7 References (1) EPRI Report 6864-L, PWR Steam Generator Tube Repair Limits: pWSCC in the Roll Transition, June 1993. (2) EPRI Guidelines for Burst and Leak Testing of Steam Generator Tubes. BAW 10226 Rev.1 50
6.0 EDDY CURRENT TECIINIQUES 6.1 Introduction Tue purpose of this section is to document the Eddy Current Testing (EC) which was performed in support of this ARC development and to define the EC field implementation for the ARC. Afler a brief presentation of the background information in section 6.2, section 6.3 covers the details of EC equipment, and acquisition and analysis processes used in the development phase. This section also presents the voltage nonnalizations necessary to compare voltages measured with different EC equipment. Section 6.3.9 presents the approach used for EC uncertainty, which results in a value of[ ]d for tube noise and analysis variability and a 15% allowance for probe wear. Section 6.4 covers the basic requisites for the field implementation of the ARC. Appendix A contains the EC technique essential variables and other details of the EC acquisition and analysis for the ARC,
6.2 Background
Extensive work has been performed by the BWOG NDE Committee to evaluate EC probe types, eddy current frequencies, acquisition parameters, methods of analysis, detection capabilities, signal-to-noise perfonnance and other aspects of eddy current as they relate to ODIGA in the tubesheet regions of OTSGs. As part of a program to optimize eddy current detection of volumetric IGA, approximately 21 ODIGA flaws from 7 pulled tubes from various operating , OTSGs were evaluated by a panel of senior eddy current data analysts. The study concluded that a mid range (MR) 0.510" diameter probe with an operating frequency range of 50-400 kilz is the best bobbin probe design for the detection and evaluation of ODIGA in OTSG tubes. The optimal sizing frequency in the region of the tubesheet where the ARC is to be applied was found to be 400 kilz. The two channel mix was Appendix 11 qualified for detection of volumetric ODIGA in the OTSG tubesheet crevice based on improved signal quality at the tubesheet secondary face. The secondary face of the tubesheet is part of the exclusion zone for the ARC. 6.3 ARC Development EC 6.3.1 Laboratory Sampic EC Process The information developed by various projects discussed in the background section 6.2 was used to define the EC process for the laboratory ODIGA samples. Multiple probe designs were used to acquire the data for developing conversions between different probes and analysis frequencies. A standard acquisition and analysis program was designed to duplicate the field acquisition equipment setup, to provide for consistency with OTSG field data acquisition, and to develop the necessary correlations for the variability of the EC techniques. BAW-10226 Rev.1 51
L i
!- A simulated tubesheet mockup was_ utilized.during the. acquisition of data to ;
. define the effect of a tubesheet on the indication signals. ;
. 6.3.2l Eddy Current Equipment
[' I L
]'
. 6.3.3- LCalibration Standards .
' The laboratory reference calibration) standard- used for the ARC sampic examination was [ ]d. This standard is designated the ' Mother.
Standard' for the OTSO ARC. - All ARC voltage level measurements including field indications calls will be referenced to this standard. Since the Mother-Standard will not be used directly for field examination calibration,- transfer standards and transfer voltages will be used for the field implementation. An EDM' calibration standard -[ ]d ' was used for the rotating; coil examination setups. , A wear ' standard [ ]d was also acquired as part of the initial calibrations. , 6.3.4 Acquisition Parameters -
- The following acquisition parameters were used for the acquisition of the ARC E sample data, s
[ e
'l
' BAW-10226 Rev.1 52
-1 m p - ..m, -
., % . - . - , ,.#~ -p .<
a b 3e.e 6.3.5 - - Analysis Technique - _ t [L I i h N 4 4 d J ,e -
. 6.3.6 Analysis Process EC measurements of the laboratory flaws were developed by a primary /
- secondary / resolution analysis process as would be done in a field analysis using the ARC analysis guidelines defined in Appendix A. On completion of the analysis process the resolution call was used in the' ARC development for structural parameter correlations. } 6.3.7 Normalization of Calibration Standards to ARC " Mother-Standard"
- A common voltage calibration is necessary for ARC applications to provide for
- : repeatability of voltage measurements. Tube pull data developed prior to the ARC projeu was normalized using-local site calibration standards. During the ARC
-development, a single laboratory calibration standard was used for the acquisition and analysis of the ARC laboratory sample data to establish ~a c~onstant voltage 5 : normalization reference. < A correlation factor between the bobbin calibration-
- standards used during the inspection at ANO-1 ~during the 1996.lR13 outage was
- . : required in order to normalize the standards to the Mother-Standard. This factor :
- was also required to normalize the voltages of the pulled tube IGA to the same -
, . scale as the laboratory samples, such that the pulled tube data might be included'
- in the structural integrity evaluations, e
i m,- h - --
- - 4 BAW-10226 Rev.1 ~53 e
y e N yr -
,e-w ,s-- av, ,n, r yv- -e
The site calibration standards which were used during the field examination of the volumetric IGA in the ARC database were collected. These site calibration standards were then examined along with the Mother-Standard using the same probes and examination hardware. The Mother Standard examination with the uncontaminated probes was performed prior to the examination of any site calibration standards to prevent contamination of the Mother Standard. I
]' The correlation between the Mother-Standard and the plant standard is shown in Table 6.
Table 6 Normalization of 400 kilz Voltage to Mother-Standard []d The data from the tube pull from ANO-1 during IR13 is shown in Table 7. The re evaluated voltages listed are from the 0.510" MR field bobbin coil inspection prior to pulling each tube. The indications on the pulled tubes were re-evaluated per the analysis methods developed for this ARC, The voltages were then adjusted to the Mother-Standard normalization by the conversion factor shown in Table 6. The final normalized voltages are the tubesheet 400 kHz MR bobbin coil voltage response that can now be used in the structural correlations for the ARC. BAW-10226 Rev.1 54
Table 7 Normalization of ANO-1 Pulled Tube ODIGA (l' 6.3.8 Normalization of Previous EC Data for ARC Purposes Previous EC inspections of OTSGs have included various types of bobbin coil probes. Additionally, freespan bobbin identified ODIGA may have been reported utilizing a different frequency than that required as part of this ARC, i.e., high frequency (llF) probes and/or 600 kilz reporting frequency, in order to make the information from these inspections useful, comparisons of probe frequencies and location of defects (with or without a si.mulated tubesheet) from the ARC laboratory samples were used to determine conversion factors for the re-nonnalization of previous data. The conversions were developed for application to previous EC bobbin voltages to determine the correct ARC voltage. The laboratory data is best for performing a comparison of this nature because of the controlled environment, i.e., the use of the same EC equipment and personnel for both acquisition and analysis. The data was re-analyzed as part of this project to remove analysis differences between the processes. The correction factor was developed to determine the affect on voltages for the development of flaw voltage distributions, growth rates, and to support the inclusion of pulled tube data in the structural ev-hiations. The following two sections define the conversions required to correct the field examination data to an equivalent ARC measurement. [ f BAW-10226 Rev.1 55
l' Figure 37 [ l' U [ BAW-10226 Rev.1 56-
. - ~ . . .-.-
1 l
-]t Figure 38 [ ~ l' ,
O' l t
-i 6,3.9 R Approach for EC Uncertainty Typical-industry practice with respect to EC uncertainty is- based upon the.
. adequacy _of a sizing model that relates the measured critical EC parameter (such Das--voltage) to the-true-structural significance as determined from destructive:
. examination.= This practice can be performed.with actual pulled tubes, or with laboratory samples that are demonstrated to.be equivalent in morphology.fThe :
approach of any voltage-based repair criteria is base _d on the relationship that the 1 voltage amplitude.and the structural significance of the degradation are dependent
. on each other and that as the more extensively degraded the tube becomes, the EC signal response becomes larger. The need for detennination of EC uncertainty.is
, ltherefore placed on those items which~may affect the voltage measurement of a . BAW-10226 Rev.1 i '57a 3 k ..
particular indication. These items are technique variability and measurement repeatability. Technique Variability Technique variability is defined as the result of any factor which causes a different eddy current signal response in subsequent examinations of a tube defect that has not changed between examinations. There are several potential contributors to this variability, including eddy current sampling density, electronic noise, probe wear and differences in calibration standards. Probe Wear Monitoring Probe wear (centering) is monitored through the us: of a probe wear standard. A calibration standard has been designed to monite vobbin coil probe wear. The standard is typically incorporated into the ASME bobbin standard and consists of 4 - 100%TW holes that are located at 0, 90,180, and 270 degrees, spaced approximately %" to 1" apart axially along the tube. During steam generator examination, the bobbin probe is used to acquire eddy current data on the wear monitoring standard. The initial (new probe) amplitude response from each of the four holes is detemiined and compared on an individual basis with subsequent measurements taken at the end of a group of tubes. Signel amplitudes from the individual holes - compared with their initial amplitudes must remain within 15% of their initial amplitude (i.e., {(worn-new)/new}) for an acceptable probe wear condition. If this condition is not satisfied, then the probe must be replaced. Based upon the probe wear criteria that has been established as part of the implementation of the voltage-based repair criteria of Generic Letter 95-05, the same methods will be utilized for the implementation of the ODIGA ARC. Upon , determining that a given bobbin probe has failed the probe wear check, all of the tubes inspected with that probe which have ODIGA indications within 75% of the repair limit must be re-inspected with a " good" probe. This rationale is conservative when addressing the issue of probe wear and its affect on ODIGA voltage response. Measurement Repeatability Measurement repeatability is a function of the analysis methods utilized by each individual analyst who analyzes a given tube defect. Potential factors that affect this variability include analysis procedures, analyst ability and training, and the signal quality of the data. Analysis variability can be assessed by using a comparison of multiple analysis of a single acquisition run on a given tube sample by multiple analysts. Minimization of the variability due to analysis training and ability is accomplished by the use of Qualified Data Analysts (QDA) during both the development and implementation of these techniques. Additionally, standardized analysis guidelines were developed as part of a BWOG NDE BAW-10226 Rev.1 58
Committee project for the purposes of utilization during this project as well as incorporation into the plant specinc analysis guidelines during an inspection of the OTSGs. A study we performed to determine the magnitude of the analysis variability. Table 8 lists the data that was utilized in the analysis variability study. Table 8 Analysis Variability Study d ll The data was compiled for each of the above sets of analysis teams. The highest variability was found in the Held data. The Geld data which was evaluated as part of the POD study discussed in section 6.2, included 5 analysis teams. [ d l luhe Noise Variability An additional variability which must be considered is the effect of tube noise on the measured signal amplitude. Tube noise is the result of minor tube dimensional or material variations or extemal variables such as deposits. Since the laboratory samples contained some inherent noise, a component of tube noise variability is present in the laboratory sample data and is obviously part of the actual tube data used in the ARC calculations. Recent evaluations of a sample of OTSG tube noise data have shown that the actual OTSG tube data has a slightly higher noise in the tubesheet region than that in the sample tubesheet mockup testing. The difference in this rms noise amplitude is a potential source of additional error in Held eddy current measurements. Since this source of potential error is random with respect to amplitude, polarity and position, its polarity and axial location would have to be critically aligned with the defect signal for the worst case effect. The treatment of this potential error is to determine the distribution of the difference between the laboratory mockup testing tube noise and that in the typical OTSG upper tubesheet. This difference distribution is then applied as an additional independent error component to the eddy current variability. [ IIAW-10226 Rev.1 59 , l
d J .c Summary of EC Variability Combining the upper 95% noise level of [ ]d with the upper 95% analysis variability of[ ]d volts yields a value of[ ]d volts. Based ca this analysis, the threshold voltages will first be reduced conservatively by 15% to account for probe wear allowances and then be reduced by [ ]d volts to account for analysis variability and potential tube noise effects. Sincethe probe wear, analysis variability and noise contribution are three independent error sources, there is considerable conservatism in this straight forward cumulative error treatment. 6.4 ARC EC Field Implementation. The. details of the field EC implementation for the ARC are contained in Appendix A. The discussion in this section covers the basic implementation requirements. The field implementation is identical to the laboratory development EC with the exception that the field implementation will be limited to a single bobbin probe design. 6.4.1 Bobbin Coil Probes In order to maximize the consistency with the ARC development data, differential bobbin coil probes with the following parameters shall be used during the
' implementation of this ARC, Other probes can be utilized provided that a properly documented equivalency test is performed and reviewed. Differential
-bobbin coil probes with diameter of 0,510" and a mid-frequency range shall be utilized. The coil widths shall be 0.060", with a nominal coil separation of 0.060"
. BAW-10226 Rev.1 60 u
between the coils. Either magnetically or non magnetically biased probes can be utilized for inspection. 6,4.2 Rotating Coil Probes Either of two technologies can be used for confirmation of volumetric ODIGA indications. A 3 coil probe, which typically contains a pancake, an axial, and a circumferential coil or a Plus-point probe can be utilized to detect and confirm volumetric ODIGA indications. Either 3-coil or Plus-point probe designs with a coil diameter, d, where d is 0.080" s d s 0.115", shall be used. 6.4.3 Calibration Standards pobbin Coil Standards ! The bobbin coil calibration standard shall be built in accordance with ASME requirements and shall include a 100%TW hole for setting phase angles, a 60%TW hole for conventional calibration curve, four 20%TW FBil for voltage normalization, and a broached support plate for the mix setup. The standard must have transfer data for the Mother-Standard. RC Standards The rotating coil calibration standard must contain a 100%TW hole for voltage normalization, four 20 % FBH for span s 2p, one 100%TW axial EDM notch, a 20%TW circumferential ID EDM notch, r. 20%TW axial ID EDM notch and a , 40%TW nxial OD EDM notch. Similar configurations which satisfy the intent of calibrating MRPC probes for OD axial and circumferential cracking are satisfactory. 6.4.4 - Acquisition Parameteis The following parameters apply to bobbin coil data acquisition and shall be incorporated into applicable inspection procedures to supplement (not necessarily replace) the parameters normally used. Test Freauencies and Mixes ( l' BAW-10226 Rev.1 61-
Dittiti7.ation Rate A minimum bobbin coil digitizing rate of 30 samples per inch. Combinations of probe speeds and data acquisition unit sample rates shall be chosen such that the following equation is satisfied. SampicRate(samplesIsec) h 30(samplesIinch) probespeed(InIsec) 6.4.5 Analysis Techniques i i BAW-10226 Rev.1 62
-~ . . . . _ _ - . -_ . .
1;
?
' ^
Y i i i i c i l' .;
~
6.5 - - References (1) EPRI TR-106589-VI "PWR Steam Generator Examination Guidelines; Revision 4, Final Report, June,1996, i (2)> ;NRC = Generic . Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generators Affected by ODSCC", August,1995. 4 m-t 4 A
'^ ^'
. iBAW iO226 - Rev 1 -
. ; 63) i
7.0 LEAKAGE EVALUATION OF TS ODIGA llot leak testing was performed at the bounding MSLB temperature, pressure, and load. The testing consisted of [d ]d laboratory ODIGA samples which had voltages from [ ] The testing also included EDM holes up to [ ]d None of the samples leaked. The axial load was increased to [ ]d and the samples still did not leak, which shows significant margin to the point ofleakage. 7.1 Introduction This section describes the methods that were used in developing a predictive methodology for main steam line break accident leakage that may occur in tubes affected by ODIGA. The intent of this section is to develop leakage correlations for IGA specifically confined within the tubesheet region. liowever, the laboratory testing was performed without the benefit of a simulated tubesheet, which could reduce the total leak rate of a given flaw. The results therefore may also be utilized in support of a generic leak rate correlation that will apply to IGA located anys.nere in a L.be, provided that testing parameters have adequately bounded all conditions. The method of evaluating leakage is based upon correlating an eddy current parameter of a given tube flaw to leak rates, using laboratory manufactured tube defects and actual pulled tube specimens. Data presented in section 4 has shown these defects to be equivalent to those which were removed from operating OTSGs. There are two key parameters associated with the development of the leak rate correlation. The first is the probability ofleak (POL), a measure of the ability of an IGA indication to leak as function ofits severity. The second parameter is the leak rate at simulated steam line break conditions, when a large delta pressure exists across the tubes and any primary to secondary leakage could be vented to atmosphere. No volumetric ODIGA indications leaked under MSLB conditions during leak rate testing of the laboratory samples performed for this task. Therefore, a POL curve and leak rate correlation necessary for a probabilistic approach could not be developed. As a result, a voltage threshold limit has been defined that precludes the possibility ofleakage. The basis for defining this threshold is presented in the following paragraphs. 7.2 Development of Bounding Leak Test Conditions liigh temperature leak testing was performed to establish expmted leak rates for ODIGA. Analyses were performed to establish axial loads to apply during these tests. Bounding conditions were established from conservative MSLB analyses that determined limiting axial loads, which are applicable to all OTSGs. A detailed description of the MSLB transient is given in Appendix B. l B AW-10226 Rev.1 64
Steam Line Break (SLB) analysis predicts that the faulted steam generator will experience an over cooling event, due to the loss of secondary side inventory, resulting in tube temperatures approximately [ ]' d cooler than the steam generator shell. The maximum tensile load occurs during the postulated transient when the tube to shell delta T is at its maximum. The difference in temperature is responsible for the large axial tensile load in the faulted loop. The resultant maximum axial loading condition on the tubes was [ ]d LB for the non-ONS units, while the ONS analysis, which utilizes different parameters due to plant operating procedures and secondary side system design, determined the load to be [ ]d LB. An analysis was also performed to determine the maximum achievable primary-to-secondary pressure differential in the OTSG. The maximum pressure differential reached during the event is [ ]* psi. This result takes into account primary safety valve (PSV) setpoint of [ ]' psig and the limiting lin tolerance of[ ]'%. These results constitute the bounding test conditions of axial load and RCS pressure, ar3 were utilized for the leak test program for the ARC. The conditions were conservatively imposed simultaneously during the leak test procedure. The analysis also considered the conditions in the unaffected team generator to ensure that the test program adequately enveloped those conditions as well. The results of the analysis showed that the unaffected steam generator conditions are bounded by the affected (faulted) steam generator, and are therefore also bounded by the leak test program conditions. The resultant test program was set-up utilizing the parameters listed in Table 9 which bound the faulted conditions modeled in the calculations. Table 9 Ilot Leak Test Parameters []d 7.3 Ilot Leak Testing System Description The experimental program utilized a leak test system to perform the testing at the conditions of actual operation of the OTSGs, including accident axial loading conditions. The system utilizes a pressure vessel to simulate actual steam generator temperature and primary to secondary pressure conditions. Ileater banks provide the necessary heat source to raise the primary system to operating temperature conditions (~600-o25 F), while heaters positioned on the outside of BAW-10226 Rev.1 65
i the pressure vessel control secondary side conditions. A hydraulic jack was connected to samples through the lower portion of the vessel to provide a means of applying the applicable axial load calculated to be present during an actual MSLB event in the OTSGs. EPRI guidelinesWwere utilized for both the design and operation ofleak testing of flawed steam generator tube samples. As previously discussed, for all non-ONS OTSG plants the bounding SLB axial load is [ ]d LB tensile. Loading conditions applicable to the ONS units [
]d LB were also tested. The leak testing was conducted by first installmg the sample in the pressure vessel, then bringing the system to MSLB temperature and pressure. The [ ]d LB axial load was then applied using the hydraulic jack.
These conditions were maintained for a minimum of one hour while the leakage, if any, was collected and measured. The axial load was then increased to [ ]d LB, and the !cakage again was measured at that condition. The test sample matrix and results are summarized in the following sections. 7.4 Leak Test Program To date, pulled tubes with volumetric ODIGA have not been leak tested under MSLB conditions. Most of these tubes have, however, been destructively examined in the laboratory to determine the extent of the volumetric ODIGA (length, width, and depth). To detennine whether or not these patches would leak under MSLB conditions, EDM patch specimens were prepared at various diam;:ters and depths to bound the field IGA extents. These EDM patches were then leak tested along with laboratory induced IGA to develop a leak rate database. As any IGA patch initiates and grows to a certain magnitude it becomes detectable through EC techniques. Such an indication has an EC signal associated with it and, as the IGA grows in length, width and depth, the EC response signal will also become larger. As flaws become throughwall, the voltage amplitude is expected to significantly increase. In order for leakage to occur through an IGA patch, the flaw must be nearly throughwall such that a break can occur during accident conditions (Axial load + Pressure). The test program consisted of fabricating a wide range of ma;mbudes ofIGA patches on OTSG tubing, and then performing a series of EC examations, including UT, conducting the leak testing under the specified conditions, burst testing all specimens and then performing destructive examinations. 7.4.1 EDM Testing EDM patches were fabricated from the same heat of material used to manufacture the laboratory 1GA specimens. The EDM patches were machined to depths ranging from approximately [ ]d %TW, with patch diameters of [
]d The severity of the EDM patches bound the potential affects of having a real ODIGA patch in a tube that is of similar depth and diameter. The BAW-10226 Rev.! 66
EDM patches are of a single uniform depth with the material removed from the OD of the tube, whereas a "real" ODIGA patch does not have any material missing from the tube OD surface, but is merely a penetration of the wall thickness extending along the grain boundaries of the microstructure. The EDM sizes exceed the size of all pulled tube samples ofIGA in all directions (LxWxD). Table 10 provides a summary of the EDM specimens that were leak tested to establish upper bound thresholds and to bound all non tested pulled tube specimens. This testing showed that [ ]d uniform penetration would be ler.k-tight under SLB accident loading conditions. These EDM holes bound the extents of all pulled tube ODIGA and thus provide the basis for including the pulled tube IGA and small laboratory IGA patches into the leak rate database, without actually leak testing the patches. Table 10 EDM Leak Test Specimens []d 7.4.2 Laboratory Sample Testing Acceptance Criteria for Laboratory Samples The acceptance criteria for the laboratory ODIGA samples was discussed in section 4, and it was demonstrated that laboratory ODIGA could be produced that adequately simulated field ODIGA. One of the criteria that must be met is that the flaw must be volumetric, with no crack like features. The leak test program utilized laboratory generated ODIGA that was induced by submerging a specimen in a corrosive bath and applying an axial load to both induce the start of the IGA attack, as well as sustain penetration of the IGA. Ilowever, in trying to generate deep enough IGA that would potentially leak, the test specimens that were to be supplied with 80-100%TW IGA contained circumferential cracks. It was apparent that the methods employed to generate deep IGA penetration caused circumferential cracking to occur in the sample in the IGA patch. The intent of the leak testing program was to develop a leakage correlation for OTSG tubes affected only with volumetric ODIGA. The mere detection of crack-like indications within an ODIGA petch would disqualify the ARC from being applied to the tube where the phenomena was detected. For this reason, samples with crack-like indications were removed from the database, since the TS ODIGA ARC states that only volumetric ODIGA indications will be dispositioned by the ARC. BAW .10226 Rev.1 67
-r- ,
I u
.5 1
iTest results for ARC Laboratory Samoles-- 4 [-
]d j No laboratory ODIGA samples leaked at either [ u ]d axial load'
- at MSLB pressure. Therefore, the POL database contains no leaking tubes and a
. POL curve and leak rate correlation cannot be developed for the indications in the -
database. For this reason, a threshold voltage repair limit for ODIGA indications in the TS region of OTSGs was developed. Based on the data presented in Table 11 a leakage threshold value of[ ]d# volts was chosen, below which flaws.will be considered not to contribute to MSLB leakage. In situ pressure testing will be - used to substantiate the adequacy of the voltage threshold to_ preclude MSLB ; g : Icakage. 7.5 Summary and Conclusions [
]d None of the laboratory ODIGA samples leaked ~ at either -[ ]d axial load at MSLB pressure. = An -
additional [ ']d laboratory samples and [ ]d tube pull indications were included
.on the basis ~of bounding EDM testing that demonstrated' that none of these additional samples would leak under MSLB conditions. Therefore, the leak rate database.contains no leaking tubes and a POL curve and leak rate correlation .
- cannot be developed for the indications in the database. For this reason, a voltage i threshold limit of- [: ]d# volts; for no leakage associated t with :ODIGA '
indications in the TS region of OTSGs was developed from the [ ]d samples. 4 presented _in Table 11. This voltage is considered to be an acceptable threshold ~ value to use to assure zero leakage. This threshold will be reduced to account for n EC uncertainties and growthi As described la section 9, indications found during > 1 the outage with voltages above the repair limit will be repaired or removed from. service. i I
- 68'
, s l BAW-10226 Rev.1 '
(. ; - 7 4
-7,6 References (1) . - EPRI Guidelines for the Burst and Leak Testing of Steam Generator :
Tubes. (2)- - NRC Draft Prop > sed Steam Generator Rule, Regulatory Guide DG 1074 Steam Generatcr Tube Integrity, August 1997.- s m BAW-10226 Rev.1 - 69: a- _ 1
l ! Table 11 OTSG ODIGA Leak Rate Database I- OTSG ODIGA Database for Leak Rate Correlations []" i i 1 l l l t l l BAW-10226 Rev.1 70
OTSG ODIGA Database for Leak Rate Correlationsy" 3AW-10226 Rev.I 71
OTSG ODIGA Databsse for Leak Rate Correlations {f i i BAW-10226 Rev.1 72 l
H.0 GROWTil RATE ANA13 SIS OF TS ODIGA A growh rate analysis is necessary to determine how much growth may occur between inspections. In this ARC, bobbin voltage is a measure ofleakage and structural integrity. Therefore, the change in voltage per EFPY must be determined. The change in voltage from 1993 - 1996 was detennined for l ]d ANO 1 UTS indications. The results show that the average voltage change per EFPY is "zero" [ ]d and the variability about this average is [ ]d. This strongly indicates that the volumetric ODIGA in the ANO l upper tubesheet is not growing. A 95% upper tolerance limit of the data, however, results in a potential growth rate of[ ]d volts /EFPY. 8.1 Introduction The ARC developed in this report utilizes hobbin coil voltage as a measure of leakage and structural integrity. As a part of any tube integrity assessment, tube degradation over time must be addressed to ensure that indications that remain in service over an inspection interval will not exceed structural or leakage limits. Therefore, bobbin coil voltages from consecutive operating cycles were evaluated to develop voltage growth rates of ODIGA indications. Due to the population of this type of tube degradation at ANO 1, it has chosen to be the lead plant for implementation of this ARC. ANO 1 has pulled tubes and confirmed the presence of ODIGA in the TS icgion. Therefore, the growth rate of ODIGA in the TS presented in this section is based upon ANO 1 specific data. The methodology discussed in this section will be r.pplied on a site specific basis during implementation of this ARC. If the plants do not have enough site specific data to develop a plant specific growth rate, the available applicable growth rate information shall be utilized in tube integrity assessments. The ANO 1 plant specific growth rates were developed by re analysis of the bobbin coil data from ODIGA indications, in accordance with the techr.lques presci.ted in section 6. Only ODIGA indications that were located within the upper tubesheet and were confirmed to be volumetric by RC. This was done to ensure that only indications attributed to ODIGA were included in the study. Once a data set of RC confinned volumetric bobbin coil indications was determined, the EC inspection history of the data set over the last three outages was re analyzed. Only those indications that were inspected at least twice during the last three consecutive eddy current inspections were utilized in the development of the growth rates. 8.2 Methodology The objective of the historical review was to assess the voltage change of ODIGA in the tubesheets of the OTSGs. Bobbin coil field data for the last three ANO-1 outages (1993, 1995, and 1996) was re evaluated per the EC techniques outlined in section 6. Because the original fic!d data was acquired using a high frequency (liF) probe and the integrity evaluations are based upon mid range (MR) probe response, it was necessary to develop a method to convert a 400 kilz S10 liF bobbin coil voltage response to a 400 kilz 510 MR bobbin coil response. This conversion is presented in section 6 of this document, and resulted in a linear relation: hip of 1:1 between these probes. The converted voltages are tabulated in Table 13 and T#31c 14 IIAW 10226 Rev.1 73
A total of [ ]d volumetric ODIG A indications in the TS were inspected during at least two of the last three EC inspections and were re evaluated for the growth study. Of the [
]d had been inspected during all of the last three inspections at ANO 1. For the evaluation, a group of five eddy current analysts re enalyzed the raw 510 liF bobbin coil data. The reported voltages were then tabulated in order to evaluate the change in voltage over the two cycles.
83 Evaluation of Voltage Change The last two rows of Table 13 and Table 14 present the average change in voltage per EFPY over the various inspection intervals. The average change in voltage over each of these intervals for both sos is between [ ]d volts /EFPY, These very small negative changes suggest that the voltage is in fact not changing. Closer examination of the data shows that only two indications (A1 A007 and Al A039) in either SO had positive voltage changes over the three inspections and five other indications (A1 A023, A1 A038, AI A079, AlB0ll, ed AlB012) that were inspected only in 1993 and 1996 showed a positive voltage change. This means only 7 of the [ ]d indications evaluated showed a positive voltage change. Figure 39 and Figure 40 show the distribution of the voltage change in OTSOs A and B. These figures include the 1993-1995,19951996, and 19931996 (if the tube wasn't inspected in 1995) inspection intervals, and show that the variance about the average voltage change is normally distributed. This variation is attributed to probe wear and analyst and ;cchnique variability, associated with independent acquisitions and analyses of the same indication over a 3 year period. Table 12 ANO 1 ODIGA Voltage Rate of Change []d Based on the similarities in the SO A and SO B data, the information was combined to fbrm an ANO 1 voltage rate of change. Table 12 shows that the standard deviations about the average growth rates are essentially constant [
]d. Figure 41 shows the distribution of the voltage change for both steam generators for the time period 1993 1996. If the voltages of these indications are truly not increasing, then EC measurement error must be the cause of the voltage variance. The variance from 1993-1996 is [ )d (the standard deviation squared).
The analysis variance is [ ]d (section 63.9). Performing an F test on this data shows that the variances are equal at a 1. sided 90% confidence limit. This infers that the analyst variability accounts for the variance in the growth rate analysis, which supports the "no growth" argument. Adding technique variability and probe wear effects to the analyst variability would only strengthen the argument that the variance is due to EC measurement error. BAW-10226 Rev.1 74
Table 13 ANO-1 SG A ODIGA Voltage Data ANO-I A Steam Generator Voltage Change []d BAW-10226 Rev.I 75
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Figure 39 ANO 1 SG A Voltagellate of Change d ll Figure 40 ANO l SG 11 Voltage Itate of Change l}# D AW-10226 Rev.1 81
Figure 41 Combined SG Voltage Rate of Change []d SA Hounding Growth Rate for Integrity Assessmen! For the tube repair limits specified in section 9 of this report, a voltage growth rate is needed, The average voltage changes for both OTSGs are shown in Table
- 12. The variances about the average growth rates are negligible if the variance due to EC measurement error is subtracted out, thus resulting in a "zero" growth rate. Ilowever, for conservatism, the 95% upper tolerance limit of the growth rate is calculated by leaving the EC measurement error in the variance. The average change in voltage from 1993 1996 for both steam generators combined is [ - ]d volts /EFPY with a standard deviation of [ ]d. Based on a normal distribution, the. growth rate is evaluated at a one sided 95% upper tolerance limit, and is
.. [ ]d volts /EFPY. The population growth rate will be evaluated during each outage when the ARC is applied, and if the growth rate has changed, the repair limit will be adjusted appropriately.
8.5' References (1); NRC J Generic Letter .- 95i05, Voltage-Based- Repair Criteria for Westinghouse Steam Generators Affected by ODSCC, August,1995. BAW 10226 Rev.1- 82:
9.0 ODIGA ARC REPAIM LIMIT AND IMPLEMENTATION STRATEGY 9.1 Repair Limit 9.1.1 Overall Approach The testing and analyses presented in the preceding sections have shown that tubes affected by ODIGA within the tubesheet are not a significant structural concern, regarding both tube burst and severance under axial loads. Therefore, the only remaining issue with tubes affected by this damage mechanism becomes leakage under postulated MSLH conditions. Laboratory and EDM samples were tested to evaluate the leakage integrity oflOA as a function of EC bobbin voltage at conditions simulating MSLil differential pressures and axial loads. As discussed in section 7, no volumetric IOA samples leaked during the tests. A correlation of leak rate w;th an EC parameter is therefore not possible with the available data. For this reason, a deterministic approach was utilized to determine a threshold voltage, below which leakage is precluded. This threshold value, in terms of bobbin signal amplitude, was based on the results of the leak testing performed on laboratory IGA. The threshold value wa; further reduced as appropriate to account for EC measurement tncertainty, and growth over one fuel cycle to determine a voltage based repair limit. Repair of all indications greater than the repair limit precludes the possibility of structural failure or primary to secondary leakage during the next planned operating cycle. 9.1.2 Voltage Threshold Value The leak test results are presented in section 7. [
]d None of the flaws leaked during the testing. An additional [ ]d tube pull samples and [ ]d lab samples were added to the database on the basis of bounding EDM testing. [
]d it is therefore concluded that flaws up to [ ]d volts will not leak, and that this is an acceptable threshold value to use to assure zero leakage.
The burst testing done on the laboratory and field IGA indicates a large margin to burst under MSLB differential pressures, even if the flaw is not supported by a tubesheet. This further suppons the conclusion that flaws up to the threshold of [ ]d volts will not open up enough to leak at these conditions. In addition, the flaws were also subject to bounding axial loads [ ]d during the leak testing, and none of the tubes failed due to tensile rupture or opened up enough to leak. It is therefore concluded ' hat the threshold of( ]d volts precludes tube severance as well, and is appropriate to use to assure both structural integrity and zero leakage. DAW 10226 Rev.1 83
9.1.3 Adjustments to Threshold Value The voltage threshold velue must be adjusted as appropriate to account for all EC measurement uncedainties associated with the chosen EC technique. In addition, an appropriate allowance must be made for growth of the indications in order to ensure that the indication amplitude does not exceed the threshold value prior to the next planned inspection. This adjustment can be expressed by the following equation: l'y = l'n,,*u - l're - l'a... Eq.9 1 L where ' l'. = Repair Limit (volts) l', = 1hreshold Voltage from Paragraph 9.1.2 (volts) I',e = EC Measurement Uncertainty (volts) IL = Growth over One Fuel Cycle (volts) From section 6, there are three basic components of EC uncertainty. The fhst is an allowance for probe wear. Wear of the bobbin coil probe allows the centerhig of the probe to vary within the tube, which changes the proximity of the probe to the flaw. This in turn will affect the amplitude of the signal response to the flaw. During implementation of the ARC, probe wear will be monitored by use of a wear standard. Variations in signal amplitude up to 15% will be accepted, but variations beyond 15% will cause the probe to be replaced. The threshold voltage value will be reduced by 15% to account for this allowed variance.13ased on a threshold value of[ ]d vults, the reduction for probe wear is [ ]d volts. The remaining componen:s of EC uncertainty are the effects of vaying signal noise amplitude and analysis variability. The efTects of these variables were studied and quantified in section 6, and it was concluded that the ccmbined uncertainty due to these two components is equal to [ ]d volts. The combined adjustment for EC uncertainty is equal to the sum of the above values. Voc = [ ]d volts From section 8.4, the bounding growth rate is [ ]d volts /EFpY. Therefore, a two EFPY operating cycle would result in a bounding growth rate of [ ]d volts /EFPY. Site specific voltage growth values are determined by multipying the growth rate by the cycle length. 13AW 10226 Rev.1 84
9.1.4 Repair ldmit Based on the discussion above, the repair limit for ODIGA is determined as follows for a plant on a 2 !!FPY operating cycle: l'u I'a,n w I'm -I'o,,a " l }' li = [ jd vohs 9.2 Implementation of Criterla During each outage the TS ODIGA ARC is implemented at a site,100% bobbin coil inspection of the in service unsleeved tubes in the applicable TS region (s) will be conducted in accordance with the requirements of Appendix A. All OD TS bobbin coil indications will be inspected with RC to characterize the morphology of the indication. e If the indication is characterized as crack like (either axial or circumferential) in accordance with the analysis protocol of Appendix A, then the ARC will not be applied. These indications will be plugged or repaired. 1
'r if the indication is characterized as volumetric, then the indication will be treated as IGA and will be repaired if the bobbin signal amplitude exceeds the repair limit defined above.
As discussed in section 5, an exclusion zone has been established wl:hin the tubesheet where the ARC cannot be applied. This exclusion zone extends from (
)d' Any indication in this location will be treated as a freespan indication, and evaluated for repair by existing site criteria. In addition, the ARC is not applicable to indications located within the rolled tube to-tubesheet joint, including the roll transition.
The voltage threshold limit defined during this outage depends on leak testing performed on laboratory samples, supplemented by available field data, in order to provide additional assurance that application of the limit continues to preclude leakage, a sample of the largest IGA indications will be tested by an in situ process that simulates appropriate site MSI.D conditions. A result of zero leakage during these tests will supplement the existing database and further support the use of the threshold voltage, ifleakage is detected during the in situ testing, the voltage threshold and repair limits will be evaluated and adjusted as appropriate to maintain and adequate margin for leakage integrity, BAW.10226 Rev.1 - 85
1 9.3 Sununary The testing and analyses presented in this report support the application of a voltage based repair limit for ODIGA in the tubesheets of OTSGs. Application of this repair limit within the guide;ines presented in this topical report will ensure that adequate margin is maintained against challenges to the structural and leakage integrity of the afTected tubes. The Al(C will be applied as follows:
- The AllC will be applicable to indications detected by bobbin coil examination and confirmed to be volumetric with a supplemental I(C examination.
- The TS AllC will only apply to volumetric TS indications [
]U (but not including) the roll transition.
. All indications meeting the above criteria will be repaired if the bobbin voltage exceeds the repair limit. Indications with voltages less than or equal to the repair limit may remain in service, and will be re-examined during the next planned inspection.
. in situ pressure testing will be used to provide added assurance that application dthe voltage repair limit continues to provide an adequate margin of safety against challenges to structural and leakage integrity.
ilAW-10226 Itev.I 86 l
- . - - = . . .. -.-. --. - - _- . .- .
B&W Owners Group Ptoprietary i APPENDIX A t ET ACQUISITION AND ANAINSIS ! A.I INTHODUCTION 1his Appendix documents the NDE techniques required for exmnination of 0TSO l tubes which may be subject to an ARC for volumetric IOA. ! A.2 DATA ACQUISITION This f.ection covers the eddy current hardware and technique required for impicmentation of the ARC. Eddy current probes, data acquisition instrument, ; and acquisition setups are discussed. l A.2.1 Eddy Current liardware i llollBIN Coll PRollE i A 0.510" diameter mid frequency range (MR) differential bobbin coil probe will be used for the data acquisition. The differential bobbin coil probe will have coils with a 60 mil axial length and a coil center separation of 60 mils. The bobbin coil probe variance shall be cenified by the vendor or will be established by testing prior to use. Alternate probe designs may be used with the appropriate testing and correlation infonnation. The bot. bin coil examination will be used for detection of the volumetric IOA indications. ROTATING Coll PRODES There are two possible rotating coil probe designs which could be used for the tube examination. Either a Plus point probe or a 3 coil probe (with pancake, axial and circumferential coils) will be used for confimtation of the indications detected by the bobbin coil examination. The rotating coil diameters will be between 80 and 115 mits in diameter and will be mid frequency range. The rotating coil probes will be used to confirm the volumetric morphology of each indication detected by bobbin coil. EDDV CURRENT INSTRUMENT The eddy current instrument will be a Zetec MlZ 30 or equivalent. The , in:trument shall be compatible with the probe designs in use it shall be capable of multi frequency data acquisition at data rates suflicient to meet the minimum ' digitizing rates.- ' s i BAW.10226P Rev.1 A1
!!&W Owners Group Proprietary EDDY CURlWNT DATA CAllLES The eddy current data cables will be low loss data cables with a maximum length of 50 feet. These cables are used with a slip ring on the probe driver, lloilillN COIL CAllilRATION STANDARD The bobbin coil calibration standards shall be built in accordance with ASME icquirements for standards and shall contain at a minimum the following items:
- One 0.052" diameter 100% through wall hole
. One 0.078" diameter 60 % flat bottom hole. The tolerance on the depth of the flat bottom hole is 10 % of the design depth. The tolerance of the hole diameter is i 0.003".
- Four 0.116" diameter 20% llat bottom holes (Filli),90 degrees cpart in a single plane around the tube circumference. The tolerance on the depth of the flat bottom hole is 20% of the design depth. The tolerance of the hole diameter is 10.003".
. The standard must contain a broached support plate for use in setup of the mix process channel, e All holes shall be machined using a mechanical drilling technique. This calibration standard will need to be calibrated against the reference standard used for the ARC laboratory work by direct testing or through the use of a transfer standard.
ROTATING C0ll CAllllRATION STANDARD The MRPC calibration standards shall contain at a minimum the following items:
- Four 0.116" diameter 20% flat bottom holes,90 degrees apart in a single plane around the tube circumference. The tolerance on the depth of the flat bottom hole is 20% of the design depth. The tolerance of the hole diameter is i 0.003".
- One 100% axial EDM notch with a 0.375" 40.010"/-0.000" minimum axial length and a width of 0.005" +0.001"! 0.002".
- One 0.052" diameter 100% through wall hole 11A &10226P Rev.1 A2
B&W Owners Group Proprietary
- One 20% circumferential ID EDM notch with a 0.375" +0.010"/ 0.000" minimum circumferential length, a width of 0.005" 40.001"/ 0.002" and a depth tolerance of 20% of the design depth, e One 20% axial ID EDM notch with a 0.375" 40.010"/ 0.000" minimum axial length, a width of 0.005" 40.001"/-0.002" and a depth tolerance of 20% of the design depth.
e One 40% axial OD EDM notch wnh a 0.375" 40.010"/ 0.000" minimum circumferential length a width of 0.005" +0.001"/ 0.002" and a depth tolerance of 0.033" or 20% of the design depth, which ever is smaller. e Similar configurations which satisfy the intent of calibrating MRPC probes for OD axial and circumferential cracking are satisfactory. A.2.2 Acquisition Setup Parameters
-[-
BAW 10226P Rev.1 - A-3 ,
ll&W Owners Group Proptietcry Y A.2.3 Probe Wear Monitoring The bobbin probes will be monitored using a probe wear standard to verify that the voltage response remains uniform around the coil circumference. If any of the voltages differ by 15 % from the initial calibration value, then the probe shall be replaced and any indications which were within 75 % of the repair limit shall be reexamined with a new probe. I f A.3 DATA ANALYSIS A 3.1 Ilobbin Coil l f IIAW 10226P Rev.1 A-4
Il&W Owners Group Proprietary I l' llAW-10226P Rey,1 A.5
Il&W Owners Group Proprietary l I s l l l i. l' E BAW 10226P Rev.1 A6
B&W Owners Group Proprietary I Y A.3.2 Rotating Coll Analysis. Plus Point I l' BAW 10226P Rcv.1- A 7-
ll&W Owners Group Proprietary l T llAW-10226P Rev.1 A ._--_______ ____________ - __________________ _ _ - __ _ ___ _ -
B&W Owners Group P:oprietary I l' BAW-10226P Rev.1 A-9
D&W Owners Group Proprietary I l' BAW-10226P Rev.1 A-10
I 13&W Owners Groun Proprietary l Y 11AW-10226P Rev.1 A-11
I Il&W Owners Group Proprietary I l' i IIAW-10226P Rev.1 A-12
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B&W Owners Group Proprietary A.4 ARC APPLICATION DENTS The ARC has not been qualified in the presence of tube denting. If an indication signal occurs at the same location as a dent signal which is distinguishable above the normal probe motion signal, then the ARC cannot be applied to the indication. MULTIPLE ROTATINO COIL INDICATIONS The ARC cannot be applied to bobbin coil indications which are detected as multiple indications by the rotating ccil examination. ROTATING COIL INDICATIONS NOT DETECTED Any bobbin coil indication which is not confirmed by the rotating coil examination will be subject to the ARC repair limit. If the Lobbin coil voltage is above the repair limit, the tube must be repaired. If the bobbin coil voltage is below the repair limit, then the indication will not require a repair action. NON-VOLUMETRIC INDICATIONS The ARC cannot be applied to indications which are confirmed not to be volumetric by the rotating coil examination. All bobbin coil indications which are not detected by the RPC examination will be treated as volumetric IOA and will be object to the ARC. ABNORMAL PIIASE ROTATION The ARC cannot be applied to indications which do not exhibit the proper phase ! angle response or phase rotation. EXCLUSION ZONE The ARC cannot be applied to indications which have an edge which is within [ Y RESOLUTION REVIEW Indications which will be dispositioned by the ARC criteria must be reviewed by the resolution analyst. The resolution analyst must confirm that the indication
- meets the conditions for application of the ARC. The resolution analyst shall
! exercise discretion to eliminate any indications which should not be dispositioned under the ARC fbr any other reason. BAW-10226P Rev.1 A-22 4
B&W Owners Group Proprietary APPENDIX B MSLil TRANSIENT The current bounding operating condition for OTSGs, in terms of primary to-secondary pressure differential, axial load, and cross flow load is the main steam line break (MSLB) transient. Analyses have been performed which determine a bounding maximum pressure differential and axial load for ANO-1, DB-1, CR-3, and TMI l. ONS 1, ONS-2, and ONS 3 utilize different analysis parameters due to plant operating procedures and secondary side system design differences, and are therefore addressed by a separate analysis. Section B.1 describes the cross flow loading which is considered generic for all plants. The cross flow is related to the location in the steam pipe and the diameter of the steam pipe. The analyses performed for determining the cross flow bounded the worst case for these conditions. 11.1 CROSS FLOW LOADING The MSLB transient initiates with the severance of the steam line. This causes a very large pressure differential between the OTSG secondary side and the downstream steam line break. The resulting accelerated flow of water and steam impose cross flow loads on tubes in the top and bottom spans (see Figure 1). These loads last for the first few seconds of the transient, when the primary-to-secondary pressure differential is approximately that of normal operating conditions, and the tubes are under a small compressive axial load. These loads produce bending moments on the tubes due to the lateral restraint of the tubesheets and tube support plates. The magnitude of the moment varies with elevation (because the cross flow load varies with elevation) and the condition of the tube. The most limiting momcat is located at the secondary face of the upper tubesheet. The more degraded this region is, the more plastic deformation the region could experience due to the bending moment. Analyses have been conducted to determine the relationship between the lateral load, the bending moment, and location within the SG. However, because this ARC will exclude portions of the tube (within the tubesheet) where the bending moment could decrease the structural integrity of an in-service volumetric ODIGA patch, a detailed explanation of this relationship is not necessary. B AW-10226P Rev.1 B-1
B&W Owners Group Proprietary Figure 1 Water / Steam Flow During Steam Line Hrcak i Pnmary inlet Nozzle > N
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' B.3. . M'AXIMUM AXIAL LOAD D' The controlling factor.in the development of tube loads-in OTSGs is the j
. temperature difference between the tube and the shell, Overcooling events such : K !as a main steamliac break result in the tubes cooling faster than the shell. This i temperature difference results in tensile loads on the tubes.
. Main steamline break analyses were performed to determine the maximum tube axial loads in OTSGs. Secondary plant differences in both the steam and e-feedwater systems resulted in two ' separate analyses being performed, one for the
- Oconee (ONS) units.and a second .for all the other OTSG plants. The generic '
inature of the second analysis results in a conservative tensile load for the non-LONS plants because plant specific controls meant to minimize overcooling events - , are not credited. :If plant safety grade control systems with " feed only' good - ~
, - . generator" logic and auxiliary feedwater initiation are taken into account, the tube
- to shell temperature differentials, and therefore the maximum tensile loads, are'
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s ,, Eminimized. jTherefore, the t loads determined from these analyses serve as 1 i [j bounding axial loads which could be reduced through site specific analyses. , The maximum tensile load is* determined by the net effects of the tube to shell
- 'sG ; temperature differential, the primary to secondary pressure differential, and axial
, ipreload, on a tube at a given point _ in time. The bounding tube axial load for the ' -
lnon-Oconee units was determined to be [? l]d LB. The analysis for the Oconee - , units determined the maximum axial load to be [ ] LB. w ; ,
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' APPENDIX C EXCLUSION ZONE ,
Bending moments exist at both tubesheet faces due to cross-flow loads during normal and faulted conditionsi- The limiting bending moment exists at the upper , tubesheet secondary face (UTS)'during a MSLB event, when the secondary side steam rapidly accelerates up through the tube bundle and then radially out of the SO through the steam outlet nozzles due to the pressure differential caused by the downstream break,_ While these lateral loads exist for only'the first few seconds -- l of the MSLB transient, they could potentially change the' condition of the . volumetric ODIGA defect that is exposed .to the high primary-to-secondary-pressure differential and axial load later in the transient. A program was therefore
- undertaken to define- the relationship between the lateral load, the bending
- moment, and the position of the defect within the tubesheet, for the purpose of defining an exclusion zone outside of which the cross-flow loads are determined to have a negligible effect on the condition of the volumetric ODIGA defect. This was accomplished by comparing the stress intensities and axial stresses due to the cross-flow loads to those imposed during leak testing. The exclusion zone defines the area where the leak testing does not bound the stress intensity and/or axial stress due to the cross flow loads. The limiting condition was determined by comparing the stress intcasities, which is presented in the following sections.
, C.1 FINITE ELEMENT MODEL An ANSYS finite element analysis was performed to determine the bending
- moment inside the tubesheet and at the UTS. [
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B&W' Owners Group Proprietary - 1 C.2' - LEAK TESTING CONDITIONS Simulated accident axial loading conditions were applied to the test specimens- .
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.i jd-C.3 MSLB CROSS FLOW :
The' maximum axial stress and stress intensity as'a function of the bending-moment will now be determined for the steam generator conditions during the - period of maximum cross flow. [ ,, e
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. C.4 STRESS INTENSITY COMPARISON ,
iWith the stress intensity during the early moments of the MSLB expressed in ~l 1 terms of the bending moment, the maximum allowable bending moment that would cause a stress intensity equal to that which is present during the testing. J l [
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- - C.51 TARC EXCLUSION. ZONE. -
( Y A Testing and analysis limits application of the OD10A ARC. to [" : i i
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