ML20212E519

Rev 3 to SG-99-04-005, STP 1RE08 Outage Condition Monitoring Rept & Final Operational Assessment

ML20212E519
Person / Time
Site:	South Texas
Issue date:	08/31/1999
From:	Cullen W, Pitterle T WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20212E516	List: ML20212E519 NOC-AE-000633, Forwards Rev 3 to SG-99-04-005, STP 1RE08 Outage Condition Monitoring Rept & Final Operational Assessment. Rept Satisfies Reporting Requirements of NEI 97-06,dtd Dec 1997
References
SG-99-04-005, SG-99-04-005-R03, NUDOCS 9909270031
Download: ML20212E519 (42)

Text

. .

SG-99-04-005, Revision 3 South Texas Project .

1RE08 Outage Condition Monitoring Report and Final Operational Assessment August 1999 l

l l

9909270031 990924 yDR ADOCK 05000498 PDR l

NOC-AE-000633,1RE08 SG Cond Monitortrv) and Op Ass. doc STI: 30947378  !

i

r-SG-99-04-005 Revision 3 Attachment to ST-WN-NOC-990091 South Texas Project 1RE08 Outage Condition Monitoring Report and Final Operational Assessment August 1999 ,

Prepared by: id/l Tkh1 W. K. Cullen

_ //

Approved by: [/. NM ' M/J'/9f T. A.Pltterie I

Westinghouse Electric Company LLC

p SG-99-04-005 R:visi:n 3 South Texas Project 1RE08 Condition Monitoring and Final Operational Assessment

1.0 INTRODUCTION

l

! Per NEI 97-06, a condition monitoring assessment which evaluates structural and leakage integrity l

characteristics of SG eddy current indications is to be performed following each inspection. This evaluation provides an assessment of the South Texas Project Unit I steam generator tube structural an_d leakage integrity based on the 1999 EOC-8 eddy current inspection results. Condition monitoring

, is " backward looking" and compares the observed EOC-8 steam generator tube eddy current indication parameters against structural and leakage integrity commensurate with RG 1.121.

Additionally, an operational assessment, or " forward looking" evaluation is used to project the inspection results and trends to the next inspection to determine primarily if tube structural or leakage  %

i

. integrity will be challenged at EOC-9. This report documents the condition monitoring and operational assessment of the NDE results from the South Texas Project IRE 08 Refueling Outage and inspection, performed in April 1999. The South Texas Project Unit 1 SGs are Westinghouse Model E2 SGs with mill annealed Alloy 600 tubing, full depth mechanical (hardroll) expanded tube to tubesheet joints, and carbon steel tube support plates with drilled tube holes and drilled flow holec 1 .

2.0 OVERALL CONCLUSIONS l

During the South Texas Project 1RE08 steam generator tube inspection, no indications exceeding the structural ir.tegrity limits for either axial or circumferential degradation (i.e., burst integrity > 3 times normal operating primary to secondary pressure differential across SG tubes) were detected; therefore, no tubes were identified to contain eddy current indications that could potentially challenge the Reg. Guide 1.121 tube integrity recommendations. Similarly, it is shown that all operational assessment stmetural and leakage integrity requirements are expected to be satisfied at EOC-9 for the

- degradation mechanisms observed at EOC-8. Based on the observed indications at IRE 08, the STP Unit 1 SGs are expected to meet all structural and leakage integrity requirements at 1RE09. The

- IRE 08 inspection of the STP Unit 1 SGs is the last ISI of these SGs prior to replacement.

3.0 PRE-OUTAGE EVALUATION OF SG DEGRADATION STATUS 1 STP 1RE08 Insocction Plan The STP 1RE08 inspection plan exceeded both the Technical Specification minimum requirements as well as the recommendations of EPRI TR-107569-VIRS, PWR Steam Generator Examination L Guidelines: Revision 5, Volume 1: Requirements. The 1RE08 initial inspection plan included; L

1 1). 100% full length bobbin examination in all 4 SGs 2)- ' 100% hot leg top of tubesheet (TTS) RPC examination, with a 43% cold leg TTS RPC sample in SGs A, and B

3) 100% Row I and 2 U-bend Plus Point examination in all 4 SGs

4) Rotating probe examination of mixed residuals (> 1.5 volts as measured by bobbin) and j

' dented intersections > 5 volts (as measured by bobbin) according to the requirements of GL 95-05. i 5)- Rotating probe examination of freespan bobbin coil indications for flaw confirmation and l

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- e SG-99-04-005 Revisian 3 characterization.

6) 100% +Pt inspection of hot leg, U-bend, and cold leg freespan dings > 5 volts

7) Tube plug visual inspection The inspection plan was developed to specifically address the areas of active degradation as well as l- areas expected to be affected based on recent industry experience as well as experience from the STP 1RE07 outage in September 1997.

Pre-Outage Degradation Assessment A pre-outage degradation assessment pursuant to EPRI GC-107621 was performed for STP 1RE08.

This degradation assessment identified the' degradation modes which could occur at STP Unit I and evaluated the adequacy of the eddy current techniques applied for detection and sizing of these -

mechanisnis.

Per EPRI TR-107569-VIRS, "PWR Steam Generator Examination Guidelines: Revision 5 Volume 1:

Requirements", an active degradation mechanism is:

1. A combination of ten or more new indications of degradation (2 20% TW) and previous indications of degradation which display an average growth rate 2 25% of the repair limit per cycle in any one SG or,

2. One or more new or previously identifW indications of degradation, including cracks, which display a growth rate equal to the repair limit in one cycle of operation.

Based upon the likelihood ofindications, the degradation assessment classified degradation mechanisms as active, relevant, or potential, with correspondingly decreasing likelihood ofinitiation and potential impact upon SG tube integrity. The degradation assessment concluded that da following degradation mechanisms were active (as defined by EPRI TR-107569-VIR5) in the STP TJnit 1 SGs.

= Axial ODSCC at TSP intersections Axial PWSCC at the TfS expansion transition down to F*

Circumferential ODSCC at the TTS expansion transition Axial ODSCC in cold leg freespan dings '-

9 Degradation Structural Limits The STP 1REOS pre-outage degradation assessment identified length and depth based structural limits for freespan axial and circumferentially oriented degradation. While an analysis to detennine the depth based structural limit (remaining wall thickness) for AVB wear which satisfies RG 1.121 has

. not been specifically performed for STP Unit 1, a lower bound value was established in the

- degradation assessment. The degradation assessment provides the structural limits and NDE uncertainties to support the_ condition monitoring and operational assessments of this report.

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3.1 1RE08 Identified Degradation Mechanisms i L Indications suggestive of the following degradation mechanisms were detected in the STP 1RE08 l inspection:

• - Axial ODSCC at TSP intersections e . Axial PWSCC Hot Leg TTS expansion transition (<1" above TTS) down to F*

-

• Axial PWSCC in the expanded tube within the tubesheet

• - Axial and circumferential ODSCC at freespan dings

. . Circumferential ODSCC at the Hot Leg TTS expansion transition e Freespan Volumetric indications e AVB wear -

. . = Wear at non-expanded preheater baffle intersections The evaluation for axial ODSCC at TSP intersections is documented in a separate ARC report, as part of analyses required per NRC Generic Letter 95-05. Identified axial PWSCC and circumferential ODSCC indications at the TTS were, in general, not sufficient in magnitude to wa: Tant in situ testing, however, some testing at this location was performed. In general, the voltage magnitudes and arc lengths ofidentified circumferential degradation at the TTS were consistent with or below previously observed limiting indication levels. This may be partly attributed to increased secondary side chemistry control as well as an effect of b reduction. Axial ODSCC at freespan dings was reported,'as well as three tubes with reported circumferential indications at freespan dings. The maximum AVB wear depth reported was 26% TW in SG A and SG D. The maximum tube wear depth reported at non-expanded preheater baffles was 10% TW in SG B, Table 1 presents a summary of the number of repaired tubes in each SG and identifies the mechanism which necessitated the repair. Table 2 presents a summary of each type of degradation mechanism observed at STP Unit I during the IRE 08 inspection. The values in Table 2 are for individual indications, and the number of tubes containing these indications will be less than the number of indications since some tubes have multiple indications. With regard to Table 2, the number of + Point confirmed indications in the TTS RPC inspection zone (l" above to 2" below the TTS ) are provided.

. Bobbin indications well below F*, are not included in Table 2. A summary of all repaired tubes,

. including tubes plugged, and tubes permitted to remain in service by application of the attemate  !

repair criteria approved for STP Uniti, TSP ODSCC per GL95-05, and F*, is provided in Table 2.

i Disposition Techniaues for Identified Degrada' tion Mechanisms  !

l Depth measurement of AVB wear indications and non-expanded preheater baffle plate wear using the bobbin coil is qualified per EPRI Appendix H standards, and these indications were sized against the 40% depth repair criteria. ODSCC indications at the TSP intersections were sized based on voltage using the bobbin coil according to guidance contained in GL 95-05. Indications greater than 1 volt by

< bobbin were RPC inspected for flaw confinnation. Indications identified in exclusion zones related to tube collapse potential near TSP wedges are RPC inspected, and ifconfirmed, are repaired regardless of voltage. Mixed residual indications >1.5 volts by bobbin were RPC inspected. All crack-like indications in the freespan, and in the expansion transition down to the F* distance were repaired upon detection since depth sizing techniques are not qualified and no ARC is applied to CATEMP\TGX 1RE06 CMOA FINAL Rev3 Non-prop. doc $

-4 g SG-99-04-005 R:visi:n 3 these regions. Location verification ofindications below the TTS or hard roll contact point, whichever is lower, for F* application is performed using the 115 mil pancake coil. Indications located greater than the F? distance below the TTS or hard roll contact point, whichever is lower in elevation, may remain in service. An eddy current uncertainty value is included in the specified F*

distance for STP Unit l'of 1.70" to determine acceptability for continued operation ofindications

- below the TTS or hardroll contact point, whichever is lower.

To reduce the potential for an axially oriented ODSCC indication to be obscured by baffle wear, all preheater baffle wear indications were RPC inspected. No hidden ODSCC was detected. Also,20%

of the AVB wear indications were RPC inspected for the same reason. No ODSCC was detected.

Indications previously called volumetric have in the past been reviewed following the inspection, and

' determined to be attributed to deposits, MBMs, dings and bulges, or tube material property changes L

- that sometimes occur after power operation. SVI calls by RPC, which did not have a corresponding bobbin MBM signal in the baseline, or could not be tracked through history, were conservatively repaired at 1RE08.

Additionally, permeability variations were repaired based on maximum voltage of the PVN, and its potential to mask a 1 volt DSI at a support plate. PVNs > 1 volt in the freespan were also repaired.

. The repair of these signals is considered conservative.

More significant than the mechanisms identified are the mechanisms not identified. These include:

• Freespan axial ODSCC at non-dinged areas and hot leg sludge pile

• Small radius U-bend PWSCC The absence of freespan ODSCC may be attributed to improved secondary side chemistry control and very low sludge and tube scale levels. The lack of small radius U-bend PWSCC is related to the in situ heat treatment of the Rowl and 2 U-bends in IRE 01.

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4.0 CONDITION MONITORING EVALUATION 4.1 Condition Monitoring Evaluation of Active Degradatien Mechanisms as Classified by the Pre-Outage Degradation Mechanism 4.1.1 TTS Circumferential Flaw ODSCC Condition Monitoring Evaluation Screening ofindications for selection as in situ test candidates is performed at STP Unit I using a methodology which is consistent with EPRI Draft Report TR-107620," Steam Generator In Situ Pressure Test Guidelines", dated December 1998. Since the publishing of these guidelines, the burst correlation for circuJnferential indications has been updated as documented in EPRI TR-107197,

" Depth Based Structural Analysis Methods for SG Circumferential Indications". The updated burst -

curve was used to develop the critical crack angle value of 277 for STP Unit I at 3AP conditions.

For in situ testing purposes, screening limits are applied to identify the most relevant subset of indications for testing. For proof test screening of circumferential indications, the first screen is crack angle 2 237 , and the second screen is average voltage (in Eddynet multiscan mode), or voltage integral,2 0.35 volts. Indications exceeding both screens are depth profiled to determine percent degraded area (PDA). Indications with PDA 2 29% are proof tested. For leak test screening, the first screen is maximum voltage in multiscan mode 21.25 volts for PWSCC,1.00 volts for ODSCC, l while the second screen is max depth 2 80% for PWSCC,75% for ODSCC. Indications exceeding j both screens are depth profiled to determine the are length at depth 2 the second screen depth limit value. Indications with are length 2 20 at the second screen depth limit are leak tested. If no indications exceed the 1" screens, the indications with the largest reported angles and largest voltages are evaluated against the second screens to ensure that all relevant indications are adequately evaluated. For circumferential indications, those that exceeded two of the three screening values were conservatively tested due to the small reported +Pt voltages.

The limiting circumferential arc length for a single,100% TW flaw, which would be expected to provide stmetural integrity at RG 1.121 guidelines for STP Unit I was identified in the degradation assessment as 277 . The in situ testing screening limit of 237 represents the limiting crack angle of 277 reduced for measurement uncertainty.

Table 3 presents a summary of the largest circumferential flaws in each SG at 1RE08. A total of 25 circumferential indications were identified. Based on phase angle analysis, all were judged to be representative of ODSCC. A total of 75 circumferentiai indications at the hot leg TTS were identified at 1RE07. The observed indications at 1RE08 represent a significant decrease in the number of observed indications.

At IRE 07, two circumferential ODSCC indications at the hot leg TTS were in situ pressure tested.

The eddy current parameters for these indications were comparable to the IRE 08 circumferential flaw parameters. The are lengths of the indications in situ tested at 1RE07 were 175 and 274 ; the maximum depths were 51% and 86%, and PDA values were 11.6% and 38.6%. The voltage integral values were 0.19 and 0.18.

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r SG-99-04-005 Revision 3 PDA values for the largest IRE 08 indications with regard to circumferential extent are provided in Table 3. The in situ test screening limit for PDA of 29% represents a 100% TW flaw of 104 arc. All flaws with a reported arc length of > 104 and voltage integral > 0.2 had PDA values calculated. All

others represent PDA values significantly below the screening value limit.

Taking the results of the circumferential depth profile, the calculated burst pressure of the limiting expansion transition indication, R26 C57 in SG C, is 5052 psi, using LTL material properties at 650 j F. The' depth and voltage profile of this indication is provided in Figure 1. The depth and voltage profile suggests that non-degraded ligaments may be present between about 200 and 220 , which, if present, have a significant strengthening effect upon the actual burst capability of the flaw. The depth and voltage profile characteristics may also suggest that if non-degraded ligaments are not present in this arc length range, the reported peak depths are likely significant depth overcalls.- ,,

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SG-99-04-005 Revision 3 Table 3 l Summary of Circumferential Flaws: STP 1RE08 Inspection Largest Reported Values for Each Parameter Given Values in BOLD Represent Indications Which Exceeded a Screening Limit SG Tube Angle Max Avg. Volts Max Depth PDA ProofTest Leak Test (from Volts (Voltage (from Profile Screen Screen Profile (+Pt) Integral) Analysis) Exceeded Exceeded al l Screening Limits 237" 1.25 (ID) 0.35 80 % l 1.00 (OD) 75 % ,

MMi A R31 C68 72* 0.19 0.12 84 % No No l No SG A indications exceeded any single screening value l B R22 C39 141* 0.2 0.10 91 % No No l B R23 C41 43" 0.23 0.19 88 % No No l B R26 C68 72* 0.28 0.26 34 % No No '

l No SG B indications selected for testing lC R3 C36 56" 0.3 0.14 93 % No No lC R23 C42 56* 0.16 0.17 51 % No No lC R18 C43 102* 0.26 0.23 73 % No No lC R22 C45 64* 0.28 0.09 100 % No No lC R20 C47 34* 0.13 0.12 0% No No lC R24 C47 43 0.2 0.17 32% No No lC R26 C53 69 0.39 0.26 73 % No No l C R26 C56 69* 0.27 0.16 49% No No I lC R26 C57 260* 0.45 0.26 99 % 51 % Yes Yes lC R23 C58 103* 0.26 0.23 80 % No No l lC R22 C73 99 0.34 0.2 25 % No No lC R23 C73 271* 0.29 0.29 64 % 24 % No No lC R21 C75 56* 0.14 0.11 12 % No No lC R22 C77 123* 0.25 0.20 45 % <5% No No '

lC R2 C88 127* 0.27 0.21 88 % <5% No No lC R13 C104 26* 0.16 0.11 49% No No l R26 C57 leak and proof tested: O leakage reported, no burst reported lD R23 C66 80" 0.28 0.17 94 % No No lD R26 C68 42* 0.37 0.15 28 % No No lD R19 C74 33" 0.14 0.11 0% No No lD R48 C79 199 0.44 0.24 43 % 14 % No No ,

l No SG D indications selected for testing C:\ TEMP \TGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 11 i

SG-99-04-005 Revision 3 4.1.2 Expansion Transition Axial Flaw PWSCC Condition Monitoring Evaluation With regard to freespan axial indications the in situ screening procedure for burst is as follows. The first two screens are crack length 2 0.49" and maximum depth 2 70%. Indications that exceed both screens are depth profiled. The average depth over the crack length is determined from the depth profile. Average depth vs. length is compared against a table oflimiting crack length and average depth relationships provided in the degradation assessment, which provide for structural integrity at RG 1.121 recommendations. The freespan screening flaw length of 0.49" provides for burst integrity at RG 1.121 reconunendations for a single flaw morphology of 100% TW depth. The screening parameters for proof testing are developed using lower tolerance limit (LTL) material property values.

For transition region indication leakage screening, the first screen is maximum + Point field evaluation voltage > 2.50 volts for ID indications,1.5 volts for OD indications, and the second screen is max depth 2 70%. Freespan OD indications were screened using a +Pt voltage limit of 1.0 volt. If  %

the second screen is exceeded the indication is depth profiled to determine length at max depth.

Indications with 2 0.1" length at the second screen max depth limit are leak tested. Axial indications located below the TTS do not represent a potential for burst. If the 1" leak test screen is not exceeded for all indications, the largest voltage indications are evaluated against the second screen to ensure that all relevant indications are adequately evaluated. The F* criterion developed for STP by Framatome concludes that a SLB leakage allowance should be considered for F* tubes. As only 3 F*

tubes were left in service, the SLB leakage contribution is considered insignificant.

At STP during the IRE 08 inspection, the longest reported indication at the TTS was in R46 C49 SG B, at 0.34"long. Based on the comparison of the IRE 08 axialindication NDE values against the in situ screening parameters, it is concluded that no axial indications identified at IRE 08 challenged structural integrity, and none would have been expected to leak at SLB conditions.

A total of 20 axial PWSCC indications were detected at IRE 07. A total of 10 axial PWSCC indications were observed at 1RE08 (9 indications in the transition,1 indication ~7" below the TTS in a wavy tube). As with the observed number of circumferential ODSCC indications at the TTS, the number of reported axial PWSCC indications has significantly decreased from 1RE07. No axial PWSCC indications at the TTS were in situ tested at IRE 07 or 1RE08. Inspection and analysis techniques were consistent for both inspections.

4.1.3 TSP ODSCC Condition Monitoring Evaluation A total of 39 indications (38 tubes) exceeding 1.0 volt were confirmed by RPC, and therefore, were plugged. The largest bobbin DSI voltages for each SG are provided below in Table 4:

Table 4 TSP ODSCC Degradation Summary SG A SG B SG C SG D Number Ind. 305 241 645 427 Largest Voltage 3.75 ,

1.49 3.77 1.78 Number 21 volt 14 8 32 20 Max 1RE07 Voltage 1.8 0.8 1.7 1.1 CATEMPiTGx 1RE08 CMOA FINAL Rev3 Non-prop doc 12

SG-99-04-005 Revisitn 3 This data shows that SG C appears to be the most susceptible SG with regard to ODSCC initiation and growth.

The voltage based structural limit for TSP ODSCC indications is 4.79 volts for a SLB AP of 2560 psi and 5.8 volts for a SLB AP of 2405 psi, where pressurizer PORVs are available (with safety factor applied).

Mixed residual indications with a bobbin voltage > 1.5 volts were RPC inspected. A less than 1 volt bobbin indication was detected in a MRI of 1.57 volts. The MRI RPC sample was expanded to 20%

of the MRIs >l.3 volts but < l.5 volts. The initial MRI RPC sample totalled approximately 190 intersections. The MRI RPC expansion included an additional 100 intersections. No indications were detected in the MRI RPC expansion program. '

4.1.4 Freespan ODSCC Condition Monitoring Other than at dings, no freespan ODSCC was reported at STP Unit I for the 1RE08 outage.

4.1.5 ODSCC at Freespan Dings ,

Axially Oriented Indications:

Axial ODSCC at freespan dings was detected in the IRE 07 outage and at the last two Unit 2 outages at cold leg dings only. As this mechanism was classified as active for the cold legs, all freespan dings required to be inspected using a qualified detection technique. Qualification of the bobbin probe as a detection tool was performed by Westinghouse, and this program achieved a POD of 90% at 90%

confidence for flaws 2 60% depth, for freespan dings 5 5 volts. Qualification was performed using i data set comprised entirely oflaboratory cracked specimens. All hot leg, U-bend, and cold leg dings

, > 5 volts were inspected by +Pt, even though this mechanism was classified as active in the cold leg only.

A total of 30 DNI (distorted ding with indication) bobbin calls were made, and a total of 16 axial indications at dings were confinned by +Pt. A total of 139 NQI (non-quantifiable indication) in the freespan were also reported by bobbin, all of which were +Pt inspected. Some of these NQI calls may have been made at dings. No +Pt axial indications with a ding voltage of < 5 volts by bobbin were missed by the bobbin. The one SAI at a ding, which was not called by bobbin, was located in a 5.2 volt ding. Only one ding SAI exceeded the freespan screening limit of 0.49". This indication (R40 C74 SG C,0.59"long,100% max depth,82% average depth,0.49" length at depth > 75%) was in situ leak and proof tested. No leakage or burst was reported. A sizing evaluation was also performed using the laboratory samples developed for the bobbin qualification program. Flaw lengths were substantially overcalled against the destructive exam lengths. A profile adjustment technique was established which considered only those depth points with coincident voltage 2 0.3 volts, for flaw maximum voltages 51 volt by +Pt, as valid depth points. The adjustment technique conservatively estimated flaw lengths when compared against destmetive exam data. Using this adjustment technique, the adjusted length of the SAI in R40 C74 SG C was 0.29", maximum depth of 97%, and length at max depth > 75% of 0.22". The unadjusted flaw lengths for all other axial ODSCC at dings was bounded by 0.41". The calculated burst pressure of R40 C74 using the unadjusted depth profile CATEMP\TGX 1RE08 CMoA FINAL Rev3 Non-prop. doc 13

M SG-99-04-005 Revision 3 was 3336 psi, for assumed LTL material properties. No burst was reported at a maximum test pressure of 4150 psi. Two additional axial indications at dings were in situ tested. Flaw characterization parameters and testing results are provided in Table 7.

Two cold leg axial ODSCC indications were in situ pressure tested at IRE 07. One was at a ding,

' 2.51" above the 11C TSP. One was not reported at a coincident ding. The indication not reported at

' a ding had a total length of 2.37"(by NDE), maximum depth of 91%, average depth of 64%, and maximum voltage of 1.96, using the 115 mil diameter pancake coil,0.86 volts using the +Pt coil.

l The calculated burst pressure at operating conditions using the as reported depth profile was 3298 psi, l using a 0.3 volt cutoff, was 3726 psi. No leakage (2840 psi leak test pressure) or burst (4070 psi proof test pressure) was reported. The reported indication at a ding had a reported length of 0.62",

maximum depth of,9,9%, average depth of 76%, and maximum +Pt voltage of 1.03. Maximum .

' leakage of 0.0033 gpm was reported. At such low levels, the validity of the positive leakage  %

l condition is uncertain. This leak rate was reported for the normal operating condition test. The leak rates for the elevated pressure test values were found to be less than this value, questioning the validity of the reported leak rate. The reported leak rate is at the lowest operating range of the leak test equipment.

In the IRE 07 inspection,7 axial freespan indications at dings were reported by bobbin and confirmed l by RPC. The bobbin technique employed for the IRE 08 inspection represents a significant increase l in detection capability compared to the technique utilized for 1RE07. Using the IRE 08 technique, all IRE 07 freespan ding axial ODSCC indications would have been detected at 1RE06. l Circumferentially Oriented Indications:

The total ding population (>0.75 volts by bobbin) for STP Unit 1 is 8297 dings, and includes cold leg, hot leg, and U-bend dings. The number of dings > 5 volts is 475. All dings > 5 volts were +Pt inspected. A circumferential indication was reported in a 3.91 volt ding, located about 2.1" below the l

bottom of the top cold leg TSP, in tube R43 C42 in SG D. A second circumferentialindication was reported in tube R42 C68, located about 14" below the bottom of the top cold leg TSP, SG C. This indication was observed in a 0.77 volt ding. Both were detected while traversing from the 11C cold leg TSP to a ding to be inspected near the 12C TSP. The NRC agreed that a 20% RPC sample of all dings was a sufficient sampling program, and requested that all reported circumferential freespan indications be in situ pressure tested. A total of approximately 815 dings were +Pt inspected as part of the initial program scope. The +Pt ding inspection was expanded to include 20% of the total ding population, or approximately 1700 dings. One additional circumferential indication was detected in R37 CSS, SG C at 6.5" below the 11C TSP as part of the expansion program. The NRC was informed of this condition, since detection of freespan circumferential indications represents a new degradation mechanism. Based on the manufacturing details, it was judged that the most likely location of such indications would be within about 25" of the bottom of the upper TSP, in Rows 30 l and greater. All dings in this region in SG C were +Pt inspected. All freespan cire indications were leak and proofin situ pressure tested to 5000 psi, or approximately 16% greater than the 3AP based circumferential flaw proof test pressure of 4315 psi. There was no reported change in the +Pt characteristics of these flaws following proof test to 5000 psi. This suggests that either the flaws are smaller than indicated by the depth profiles or could possibly be false calls. A summary of the pre  !

and post in situ test NDE results are provided in Table 5 for these flaws. A graphical representation of the pre and post NDE depth profiles for these larger indications is provided in Figures 2,3, and 4. l C:\ TEMP \TGX 1RE06 CMoA FINAL Rev3 Nonprop. doc 14

o 3 .

SG-99-04-005 Rsvisi:n 3 Figure 2 shows that for the case of R42 C68, that the depth profile suggests that the deepest reponed depths at the edges of the indication may be overcalled. The voltage response indicates the peak

, voltage at the center of the indication arc involvement, however, the deepest reported depths are called at the edges of the indication, where the voltage is essentially zero. This trend is also eviden:ed in R43 C42 and R37 CSS, but is not as apparent as for R42 C68. For indications with voltages as small as these, the sizing and repeatability erTor can be large. This is shown by comparison with the results of R43 C42. The post in situ test PDA is 15.14%, while the pre in situ test PDA is 23.85%. The post in situ voltage is reduced to 0.51 volts from 0.53 volts pre in situ. The slight apparent PDA growth for R42 C68 (0.5%) is certainly within repeatability bounds. If any cha,pp were expected, it would be most likely to occur in R43 C42 or R37 C55, which had substantially larger reported indications compared to R42 C68. Another abnormal characteristic of these indications is the shape of the voltage profiles. The voltage profiles exhibit nearly identical shapes for all three reported circumferential indications at freespan dings. When compared with the -

voltage profile for R26 C57 (hot leg TTS circumferential indication) shown in Figure 1, it is seen that the voltage profile for this indication, representative of degradation confirmed by tube pull, is significantly different from the voltage profiles of the freespan circumferential indications. For both of the larger indications, the PDA value was reduced following in situ testing.' Although the expansion program performed for circumferentially oriented cracking in freespan dings did not meet the Table 3-2 expansion criteria of the EPRI Rev. 5 ISI guidelines, the expansion program, coupled with in situ testing was judged satisfactory by the NRC.

The bobbin ding volteges for R42 C68 and R37 C55 were 0.77 and 2.15 volts, respectively. The bobbin ding voltage for R43 C42 was 3.91 volts. These voltages are similar to the pre-crack +Pt ding voltages of the bobbin qualification samples. It is expected for flaws of this reported depth (at or near 100%), that significant voltage response increase would be encountered. The pre vs. post crack +Pt data for the bobbin qualification samples showed that for those samples at the threshold of bobbin detection, that the post crack +Pt data voltage was approximately twice the pre crack +Pt voltage.

These contributing factors tend to show that if these indications are representative of true degradation, that the degradation depths are grossly overestimated by the NDE process.

CATEMP\TGX 1RE06 CMoA FINAL Rev3 Non-prop.cloc 15

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SG-99-04-005 R:visirs 3 4.2 Condition Monitoring Evaluation of Degradation Modes Classified as Relevant in the Degradation Assessment i The degradation assessment concluded that the following mechanisms did not meet the criteria to be classified as active mechanisms, and therefore were categorized as relevant mechanisms.

• AVB wear

. Tube wear at non-expanded preheater baffles

• Small radius U-bend PWSCC i e Axial ODSCC at dented TSPs > 5 volts e Tube wear due to foreign objects / loose parts .

Condition monitoring of relevant mechanisms indicates that no indications were present at 1RE08  !

that represented a challenge to structural integrity or leakage integrity.

The AVB wear mechanism at STP Unit 1 is rather benign. A total of only 19 AVB wear indications were reported, with a maximum reported depth of 26% TW. The average AVB wear growth rate for  ;

previously reported indications is 1.6% TW/ cycle, with a 95% cumulative probability growth of j 11%TW/ cycle. No new AVB wear ic.aications were reported.

No small radius U-bend PWSCC indications were reported.

No tube wear due to foreign object wear was reported.

Tube wear at non-expanded baffles represents a very low growth mechanism. The largest reported depth at 1RE08 was 10% TW, The average growth rate for all indications combined is 0%, while the largest reported growth is only 3% TW.

4.3 Condition Monitoring Evaluation of Degradation Modes Classified as Potentialin the Degradation Assessment The final degradation class addressed in the degradation assessment is potential degradation modes.

Potential degradation modes are those not seen in STP Unit 1, but do represent a potential to occur based on experience at other plants or in laboratory testing.

The only degradt. tion mode classified as potential for STP 1RE08 is cold leg TTS SCC. A 43% RPC sample inspection was perfomied in the cold legs of SGs A and B. No indications were reparted.

C:\ TEMP \TGX 1RE08 CMOA FINAL Rev3 Non-prop.dsc 18

SG-99-04-005 Revisi::23 4.4 Summary of Limiting Indications The following Table 6 presents a summary of the limiting indications for the IRE 08 inspection.

Table 6 Summary of Limiting Indications l

Mechanism Max Max Depth Avg. Depth Calculated Burst SLB Leakage gpm Length Pressure (95%, Nom,BestEst)

Cire ODSCC at 258 99 % 51 % 6038 psi

• O (in situ test) hot leg TTS Axial PWSCC 0.34" 100 % 79.7 % 5052 psi 0.854,0.086,0.033 I at TTS ODSCC at 0.59" 100 % 86 % 3336 psi ** O (in situ test) dings AVB Wear 0.4" 26 % 26 % 9800 psi 0 (assumed)

Circ ODSCC at 117" 99 % 24 % (360" 7500 psi *** O (in situ test) freespan dings basis)

• Successfully proof tested at a test pressure of 4315 psig. No leakage reported at 2925 psig.

• • Successfully proof tested at a test pressure of 4150 psig. No leakage reported at 2841 psig.

l

\

• • • Successfully proof tested at a test pressure of 5000 psig. No leakage reported at 2925 psig. Post in situ +Pt examination indicated that no change in indication characteristics was observed.

l 4.5 SLB Lenkage Discussion:

For other than TSP ODSCC indications, any potential for SLB leakage at end of Cycle 8 conditions is  !

judged negligible. The circumferential ODSCC indications at the TTS are of sufficiently low '

magnitude that no leakage contribution is expected. This was confirmed by in situ test of the limiting l cire flaw at the TTS. No leakage was reponed at a maximum pressure of 2925 psi. The limiting l axial flaw at the TTS had a 115 mil pancake coil maximum voltage of 3.58 volts (estimated +Pt volts l of 2.15 volts) and length at depth >80% of 0.25". The lead-in/ lead-out effects of the coil tend to  ;

overestimate the flaw length. Using a 1 volt cutoff representing depth >80%, the best estimate length  !

with respect to leakage potential is approximately 0.2". The limiting axial ODSCC flaw at a ding had a maximum +Pt voltage of 0.64 volts and length of 0.59". The lead-in/ lead-out effects are well documented in the ding qualification report, SG-99-03-005, and indicate that a voltage cutoff of 0.3 volts can be used to accurately assess true flaw length. The total flaw length is estimated to be 0.29", I with a length at depth >75% of 0.22".

l l For the leakage estimates of Table 6, the unadjusted flaw length and depth profiles are used to

! calculate the 95% confidence SLB leakage and mean leak rates. The adjusted flaw lengths exceeding l the leakage threshold depths are used with the mean leakage correlation to assess SLB leakage against l

C:\ TEMP \TGX 1RE08 CMOA FINAL Rev3 Non-prop doc 19 I

L

b ,+ )

l= SG-99-04-005 Rzvlsi:n 3

( the FSAR value of 1.0 gpm total,0.35 gpm in the faulted SG. j l  :

SG A:

Only one indication in SG A was judged to have a potential to contribute primary to secondary

' leakage during a postulated SLB event. This tube, R14 C73, had 4 axial indications located at ~7.25" l l: below the TTS. .The lengths and maximum voltages (115 mil pancake coil) of the four indications

! was' 0.37",4.52 volts,0.38",3.55 volts,0.41"/ 4.93 volts, and 0.48",7.72 volts. Based solely on the reported lengths, assuming the flaws existed in the freespan, SLB leakage at 95% confidence and l using mean values are 7.483 gpm and 1.338 gpm for these four flaws combined. Using a voltage i cutoff of 4 volts for assessment of TW length, the estimated TW lengths for the four flaws are 0.13",

0.0",0.17", and 0.27". Iflocated in the freespan, these four flaws would have expected leakage during a postulated SLB event of about 0.06 gpm using mean leak rates,0.8 gpm at 95% confidence. N These flaws were identified in a " wavy" tube (as termed by STP). These tubes have reported abnormal expansion profiles from R'C testing, which could suggest that the tube is not in contact

with the tubesheet over the entire circumference. The F* criterion is not applied to wavy tubes. It is expected that some leakage restriction capabilities in these wavy tubes is present, but cannot be quantified. Nonnal operation leakage from these flaws for freespan conditions is expected to be about 0.006 gpm using mean leak rates and about 0.08 gpm at 95% confidence. As virtually non-measurable (<1/2 gpd or <3.5 x 10" gpm) primary to secondary leakage was measured during the cycle, the leakage restriction in the wavy tubes is judged to be substantial. j SG B

One axial PWSCC indication at the TTS in SG B, R46 C49 was judged to have a high probability of leakage at SLB conditions, however, its likelihood to provide leakage at normal operating conditions isjudged low. The maximum voltage of this indication was 3.58 volts (115 mil pancake coil voltage), maximum reported depth of 100%, and total length of 0.34". The flaw average depth was 79.7% TW. As the reported length of this indication is considerably less than the flaw length that provides burst capability at the 3AP value for an assumed 100% TW flaw, TW over the entire length of the flaw, structural integrity is expected to be provided. Using a voltage cutoff of 4 volts for assessment of TW length, this flaw would not be expected to leak at SLB conditions. The restraint provided by the hardroll process acts to reduce the potential leakage from axial flaws in the transitSn by preventing the lower crack tip from opening. Roll transition axial PWSCC flaws at similar plan;s

' with +Pt voltages up to about 4 volts (about 6 volts for 115 mil pancake coil) did not leak at SLB conditions.

~ One axial flaw at a ding in SG B (R47 C30), was judged to have a limited leakage potential. This flaw had a maximum +Pt voltage of 1.19 volts. Based on the lab samples generated as part of the

- bobbin qualification program for detection of axial ODSCC in freespan dings, this +Pt voltage is representative of degradation of about 85% TW. If the flaw were assumed TW over the entire l~ reported length of 0.3", the SLB leakage at 95% confidence would be about 0.5428 gpm, and about 0.0585 gpm using mean leak rates. Using the length adjustment procedure described above, the flaw length at > 0.3 volts is 0.22". If the flaw were assumed TW over the entire adjusted length of 0.22",

l the SLB leakage at 95% confidence would be about 0.206 gpm, and about 0.036 gpm using mean j leak rates. Based on the reported maximum +Pt voltage of 1.19 volts, SLB leakage would not be

- expected from this indication.

CATEMRTGx 1RE06 CMOA FINAL Rev3 Non-prop. doc 20

SG-99-04-005 Rzvisix 3 j l i One F* tube was identified in SG B. The SLB leakage contribution of a single F* tube is on the order  !

of 2.3 x 10* 3pm, and will not have an impact to estimated leakage. Therefore, F* tube leakage will  !

i not be considered in the final leakage evaluation.  ;

i Therefore, no SLB leakage contribution from indications in SG B, other tb : at TSP intersections,is  !

expected.  !

l SG C:  !

No axial indications were observed in SG C at the hot leg TTS. Only two axial ODSCC indications at freespan dings were judged to represent a leakage potential; taese indications were located in R40 I C74 and R37 C43. The +Pt voltages for these two flaws were 0.64 and 0.79 volts. Both flaws.were - j in situ leak tested with no reported leakage. The indication in R40 C74 was also proof tested. No

structural failure was noted.

l One F* tube was reported in SG C.

1 SG D:

(. Of the 4 axial PWSCC indications at the hot leg TTS, the maximum reported voltage using the 115 l 0 pancake coil was 1.18 volts. The maximum depth and depth profile do not support leakage for this 1 indicction. Only two axial ODSCC indications at freespan dings werejudged to represent a leakage potential; these indications were located in R42 C19 and R32 C39. R32 C39 was in situ leak tested with no reported leakage. The indication in R42 C19 was reported in a 52 volt ding and was not in  :

situ tested due to the interference of the ding upon installation of the leak testing mandrel. The  !

maximum voltage"of the indication was 0.58 volts, with 100% depth calls extending for l l approximately 0.2" of the total flaw length. The influence of such a large dent suggests that the depth

. j

~

l - profile may be unreliable. Assuming the flaw was throughwall over the entire length, the 95%

confidence and mean leak rates at SLB conditions are 1.316 gpm and 0.159 gpm. If the voltage

! response of R42 C19 is accurate, SLB leakage is not supported, as more limiting indications (with l respect to flaw voltage) were in situ leak tested both at IRE 07 and IRE 08.

l l One F* tube was reported in SG D. l c

Comparison Against NEI97-06 Leakage Allowance: )

! i

( The total estimated SLB leakage at 95% confidence from indications detected but not in situ tested is  !

l 0.8 gpm for SG A~ 0.0 gpm for SG B,0.0 gpm for SG C, and 1.316 gpm for SG D. The total estimated SLB leakage using mean leak rates from indications detected but not in situ tested is 0.06 gpm for SG A,0.0 gpm for SG B,0.0 GPM for SG C, and 0.159 gpm for SG D.

1 Per NEI 97-06, postulated SLB leakage should remain below the site specific leakage allowance  ;

corresponding to offsite dose consistent with the 10 CFR Part 100 guidelines, and calculated in a manner consistent with NUREG-0800, the Standard Review Plan. The site specific dose allowance i for STP Unit 1 is 15.4 gpm in the faulted loop. The largest SLB leakage contribution from non-ARC i degradation mechanisms not in situ tested is postulated for SG D, and is approximately 1.316 gpm l l

CATEMP\TGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 21 l

n SG-99-04-005 Revision 3 using 95% confidence leak rates. The projected SLB leakage contribution for SG D for TSP ARC j indications is less than 4.4 x 10'3 gpm, which is the TSP ODSCC SLB leakage contribution for the limiting SG (SG C) for TSP ODSCC. Therefore, the accident condition leakage requirements for dose considerations are satisfied.

Currently, it is also required that FSAR leakage limits be satisfied for nominal leak rate calculations.

i The FSAR limit is 0.35 gpm in the faulted loop,1 gpm total. This allowable limit exceeds the largest l predicted nominal leak rate of 0.159 gpm for SG D. l The curTent licensing basis for STP with regard to non-ARC leakage sources during a postulated SLB event is 0.35 gpm in the faulted loop,0.65 gpm in the intact loops. The referenced leak rate is an average value over the total release time, therefore, comparison against average postulated leak rates ,,  ;

from non-ARC mechanisms is acceptable. As the maximum projected SLB leak rate for non-ARC

• l mechanisms is 0.159 gpm in SG D, and is far less than the allowable limit of 0.35 gpm.

In Situ Testing Summary:

The in situ testing performed for the IRE 08 outage helps to support the conclusion that postulated SLB condition primary to secondary leakage will remain below I gpm for all SGs. A summary of the leak and proof testing parameters is provided in Table 7.

l

{

i C:\ TEMP \TGX 1RE06 CMOA FINAL Rev3 Non-prop. doc 22

r SG-99-04 005 R .visia n 3 5.0 1RE08 CONDITION MONITORING CONCLUSION and FINAL OPERATIONAL ASSESSMENT As the original STP Unit i SGs will be replaced in Spring 2000, the 1RE08 inspection was the last ISI of the original STP Unit 1 SGs. Based on the STP 1RE08 inspection results, no tubes contained indications which represented a challenge to structural or leakage integrity and all condition l monitoring requirements are satisfied. The relative severity levels of the observed degradation were l substantially below the levels associated with the IRE 07 inspection. Based on the apparent decreased or non-increasing expansion transition ODSCC and PWSCC growth and initiation rates, it is unlikely that a substantial increase in either number ofindications or growth rates would be encountered during Cycle 9. The, Cycle 9 operating period is a maximum of 333 EFPD, vs. 525 EFPD operating period for Cycle 8. As no degradation mechanisms challenged structural or leakage integrity at -

1RE08, the likelihood of an indication posing a challenge to structural or leakage integrity at the end of the Cycle 9 operating period is considered negligible. The number of circumferential ODSCC indications at the hot leg TTS reported at IRE 08 was 3 times less (25 vs. 75) than the number of circumferential ODSCC indications reported at IRE 07. The number of axial PWSCC indications at the hot leg TTS reported at 1RE08 was half (10 vs. 20) of the number of axial PWSCC indications reported at 1RE07. The number of confirmed axial ODSCC indications at freespan dings increased from 1RE07 (16 vs. 7), however, the enhanced bobbin inspection technique utilized at IRE 08 accounts for this increase. All of the axial ODSCC freespan indications at cold leg dings reported at IRE 07 would have been identified at IRE 06 had this technique been utilized in 1996. The observance of suspected circumferential ODSCC indications at freespan dings between the 11C and 12C TSPs did not represent a challenge to structural or leakage integrity. Assuming these indications are representative of true degradation, the minimum burst pressure for these reported indications is ,

approximately 7500 psi. As in situ testing of the limiting indications at 1RE08 showed no leakage for leak test pressures ranging from 2841 psi to 2925 psi, and showed no evidence of structural failure at proof test pressures of 4150 psig to 5000 psig, stmetural and leakage integrity requirements of NEI 97-06 were met using deterministic methods.

Despite the apparent confirmation that structural and leakage integrity consistent with NEI 97-06 and the current STP licensing basis, growth rates for the observed SCC mechanisms were evaluated for the Cycle 8 operating period. Assessments of growth are provided in the following section. In general, the growth rates appear to be decreasing compared to previously performed analyses. This observance, coupled with a Cycle 9 operating cycle of only 333 EFPD (compared to a 525 EFPD operating length for Cycle 8), can be used to deterministically conclude that the SG tubes will continue to meet all industry and regulatory structural and leakage integrity requirements at EOC-9.

5.1 Growth Assessment of Limiting IRE 08 Indications and Operational Assessment Evaluation l Circumferential ODSCC at the TTS i The 4 largest arc length circumferential indications (> 100 arc) and one with a reponed depth of 10% from pmfile analysis reported at the hot leg TTS were reviewed for arc length growth. The j 1RE07 hot leg TTS RPC data (115 mil pancake coil) was reviewed to deteimine if these flaws were present; all were determined to be observed using the IRE 07 data, based on the knowledge of a C:\ TEMP \TGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 23

r SG-99-04-005 Revisi:n 3 somewhat larger flaw being present at the IRE 08 inspection. As only 115 mil pancake coil data was available from the IRE 07 inspection, the 115 mil pancake coil data from 1RE08 was used for the growth evaluation. Plots of circumferential extent vs. depth for the IRE 08 and 1RE07115 mil

. pancake data are provided in Figures 5 thru 9. This data is developed from circumferential direction depth profile analysis. Based on the growth evaluation, the average and maximum are length growths

are 22', and 42 , while the average and maximum PDA growths are 3.4% and 6.4%. It should be noted these values apply to the largest indications at 1RE08. The average and maximum, max depth growths are 13% and 55%.

, A total of 29 tubes with circumferential indications from STP Unit 1, IRE 06 and 1RE05 inspections are included in the growth database of EPRI TR-107197. The average PDA growth for the 115 mil pancake coil was 16,.1%, with a maximum value of 68.9%. The Cycle 7 circ flaw growths were .

evaluated in the 1RE07 condition monitoring report. This evaluation, totalling 35 flaws, showed the  %

largest PDA growth using the 115 mil pancake coil was 11.22%. Considering all PDA growths, the

- average value is 0.6%. Using positive PDA growths only, the average value is 3.4%. Therefore, these growth data suggest that the growth characteristics have been reduced or constant in the most

- recent cycles.

l From Figures 5 tinu 9, the Cycle 8 growth appears to be modest. The cire flaw in R48 C79 SG D (Figure 9) appears to show essentially no change. The only feature of note is that the 115 mil pancake coil data of IRE 07 indicates ID phase angles over the entire profiled length, whereas the 1RE08115 mil and +PT data indicates OD phase angles over the entire profiled length.

l

Table 8 provides the growth data for the 115 mil pancake coil data for Cycle 8. All data is developed  ;

from circumferential direction depth profile analysis, with the exception of the flaw voltage, which is i the reported peak from the production data. Table 8 also provides +Pt data from profile analysis and l compares these values against the IRE 08 and 1RE07115 mil pancake coil data from profile analysis.

Even though this mix of coils would be expected to overestimate growth rates due to the increased i +Pt detection threshold, the growth rates are modest and support conclusions from the 115 mil pancake coil data. In general, the +Pt and pancake coil data are similar. Two flaws however are not similar. Substantial differences in PDA are seen when there is a large difference in are length, and

most likely attributed to shallow tail detection by +Pt. One (R26 C57) of the two indications with

! large disparities between the +Pt and 115 mil pancake coil arc lengths has about 90 of flaw length at l the tails which produce ID phase angles, and could be overcalls. The other flaw with large PDA l variances between the +Pt and 115 mil pancake data has a reponed +Pt PDA of only 24%. j PDA is the controlling parameter considering burst capability of circumferential flaws. From the 115  ;

mil pancake coil data, maximum PDA growth of 6.4% was reported. Plus Point coil PDA evaluation l t from 1RE08 indicates that only 1 indication (R26 C57) had a reponed PDA value exceeding 25%, I and that this flaw may include overcalls at the tails of the indication in the evaluation based on the j' reponed ID phase angle at the ends of the flaw. Assuming a PDA detection threshold of 20%, the maximum PDA value at IRE 09 is expected to be approximately 27%, far less than the 77% PDA limit for a single 100% TW circumferential flaw. When the Cycle 9 length of 333 EFPD is i considered, a maximum PDA assessment for EOC-9 of about 25% is obtained. Per EPRI TR- j 107197, the maximum PDA uncertainty for the STP Unit 1 pulled tubes using the 115 mil pancake {

coi? 's about 30%. Therefore, considering PDA measurement uncertainty at IRE 08, a maximum, )

actual PDA of about 55% is estimated for EOC-9. ]

l 1

CATEMF%TGX 1RE08 CMoA FINAL Rev3 Non-prop. doc 24 i

(, i

E SG-99-04-005 R:visizz 3 Pulled tube data from the 1995 inspection shows that circ cracking of max depth 55%, PDA 31% was readily detected using both the 115 mil pancake coil and +Pt coils. Cire cracking of max depth 41%,

PDA 19% was not detected in the field using the 115 mil pancake coil. Ligament corrected PDA for the detected flaw is 15.3%L Ligament corrected PDA for the non-detected is not available.

Therefore, use of a PDA detection threshold of 20% is reasonable.

As the limiting circumferential flaw at the expansion transition was in situ leak and proof tested with no evidence ofleakage or burst, and more limiting indications have been leak tested in the past with no evidence ofleakage, circumferential ODSCC at the TTS is not expected to contribute to SLB conditions leakage at EOC-9.

' Axial PWSCC at th'e TTS -

By far, the largest, and only axial PWSCC flaw with a leakage potential was R46 C49, SG B. The following table presents the growth data for Cycle 8.

As no flaws with length approaching the freespan 100% TW flaw length of 0.49" were reported at 1RE08, a consistent result is expected following the Cycle 9 period. Assuming an undetected flaw

- length equal to the coil field, approximately 0.12", a maximum flaw length of 0.31" would be expected at IRE 09, and therefore, structural integrity would not be challenged. Pulled tube destructive exam data for axial PWSCC at the TTS has consistently shown the NDE to overestimate l the flaw length. Therefore, no axial PWSCC flaws at the TTS are expected to approach the 100%

TW axial flaw critical length of 0.49".

STP Unit 1 Axial PWSCC at TTS Growth Rates: 115 mil pancake coil 1RE08 1RE07 (Lookback Analysis)

Length Max Depth Max Volts Length Max Depth Max Volts j R46 C49 0.34" 100 % 3.58 0.17" 20% (1) 0.60 R36 C53 0.19" 100 % 0.71 0.15" 40 % 0.40 L R28 CS2 0.25" 80% (1) 1.18 NDD NDD NDD Growth Length Max Depth Max Volts '

R46 C49 0.17" 80 % 2.98 R38 C53 0.04" 60 % 0.31 1

- R28 C52 -- 0.13"(2) 74% (3) 1.18 (1): Depth at max volts. Best estimate of max depth is about 40% TW.

(2): Length growth based on detection threshold equal to coil field of 0.12" (3): Depth growth based on detection threshold of 20%

CATEMP\TGX 1RE08 CMOA FINAL Rev3 Non prop. doc 25

i SG-99-04-005 Revision 3 Axial PWSCC Within the Tubesheet in Wavy Tubes l The bobbin data for R14 C73, SG A was reviewed for 1RE07 and 1RE06. Bobbin parameters are i provided in Table 9. This data shows '.he indication was present in 1RE06, and would also suggest l that some measure of growth occurred since 1RE06. The voltages were measured using the max rate function, and therefore, may underestimate the voltage if measured on a peak to peak basis. The bobbin graphics show an increasing progression of expansion or opening of the lissajous figures, also suggesting that some growth occurred over this period. As with roll transition regions, the flaw length at roll overlap regions is expected to be limited based on the limited available stress field axial length. This is shown by the reported flaw lengths. At the TTS, the longest reported flaw was 0.34",

whereas the flaw lengths for the 4 separate indications in R14 C73 at 7" below the TTS ranged from 0.37" to 0.48". Three of the four flaws were comparable to the flaw in R46 C49 in length, max depth, and max volts. As no reliably measurable leakage was reported in SG A, it can be concluded that  %

only the largest flaw had any leakage potential at SLB conditions, and that only about 0.20" of this length is considered to potentially leak. As the bobbin data for R14 C73 indicates the flaw was present since 1 RE06, the growth is considered in depth only.

Table 9 l R14 C73 Axial PWSCC within tubesheet in wavy tube Bobbin Data 1RE08 1RE07 1RE06 Parameter (max rate) (max rate) (max rate) l Mix Volts 7.80 6.81 _

5.82 Mix Depth 89 % 84 % 63 %

l 550kHz Volts 7.08 5.42 6.27 550 kHz Depth 87 % 79 % 59 %

130 kHz Volts 4.99 4.01 1.08 130 kHz Depth 50% 43 % 29 %

Thic data suggests that additional growth occurred during the period from the IRE 06 to the 1RE08 it.: , ections. Based on bobbin data alone, it cannot be determined if the growth occurred in length, depth, or a combination of both.

l Dine ODSCC The bobbin data from 1RE07 were reviewed for the two ding ODSCC flaws that were in situ tested. I Both indications would have been reported at IRE 07 had the new ding inspection technique been I

utilized at IRE 07. The IRE 07 low frequency differential (130 kHz) voltage and phase responses for these two indications were 0.97 volts,107 , and 0.56 volts,91. Low frequency differential response for the first flaw at IRE 08 was 0.94 volts,103 . The second flaw was called using the mix. The l l 1RE07 mix response was 1.28 volts,160 , the IRE 08 mix response was 1.34 volts,142 . As the l

1RE07 data for these flaws indicates detectability (i.e., max depth > 50 to 60%) and the reported +Pt depths from IRE 08, a bounding estimate of max depth growth is ~30% TW/ Cycle. Adjusted for the I Cycle 9 length of 333 EFPD, a bounding estimate of max depth growth is approximately 19% TW. l C:\ TEMP \TGx 1RE08 CMOA FINAL Rev3 Non-prop. doc 26

SG-99-04-005 R:visim 3 The bobbin qualification program showed that the length of the ding flaws was bounded by 0.375" Therefore, ding flaw lengths are not expected to approach the freespan critical flaw length of 0.49".

' Use of the new bobbin technique has been shown to provide an enhanced detection capability compared to previous inspections. Laboratory testing has shown the ding flaws to be limited in axial length due to the limited stress field in the axial direction.

.5.2 Operational Assessment Conclusions The condition monitoring analysis of the limiting IRE 08 indications has concluded that all flaws had burst capability exceeding the 3AP requirement, and maximum SLB condition primary to secondary leakage of 0.159 gptn in SG D was below the FSAR analyzed limit. of 0.35 gpm for non-ARC .

mechanisms. As all pedinent operating parameters are expected to remain unchanged for Cycle 9, and considering the shonened Cycle 9 operating period of approximately 333 EFPD, it is expected that all structural and leakage integrity requirements will be met at EOC-9. This conclusion is further supplemented by the growth analysis of non-ARC mechanisms which suggest the degradation ,

mechanisms observed for the recent inspections at STP Unit I do not indicate an increasing growth rate. Therefore, it is concluded that all structural and leakage integrity requirements are expected to be met at EOC-9.

6.0 Potential New Degradation Mechanism Assessment During the STP 1RE08 inspection, a total of 9 SVI calls were reported at TSP interse:tions. At STP, a SVI call is a RPC indication that cannot be resolved as axial or circumferential in nature. SVI calls are typically accompanied by bobbin indications suggestive of degradation (NQI), and this bobbin signal triggers the RPC inspection. Of the 9 SV1 calls mentioned above,7 had co responding bobbin NQI calls, I associated with a dent, and the remaining SVI(R40 C74 at 18C) had no corresponding bobbin indication in history. A bobbin DNI (distorted ding indication) was reponad in this tube (R40 C74) at approximately 2" above the 18C plate. +PT inspection confirmed axial OD2CC at the DNI call (2" above the plate). For all of these NQI/SVI calls, the bobbin voltage exceeded the +Pt voltage.

The range of bobbin to +Pt voltage ratios was 1.0 to 6.7 with an average ratio of 2.74, and is typical of axial ODSCC at TSP intersections. The average and maximum bobbin mix channel amplitudes of these NQI/SVI calls was 0.55 volts, and 0.80 volts, respectively. The maximum +Pt voltage for these indications was 0.69 volts. These maximums both occurred in R1 Cl4, SG B, at 14C -0.37".

The bobbin data for all other (not at TSPs) SVI calls were reviewed to determine coincidence of NQI, DNI, DNG, or DNT calls. For those with corresponding NQ1 calls, the bobbin amplitude exceeded the +Pt voltage, with the maximum bobbin amplitude for the mix channel estimated to be 2.61 volts based on a reported 130 kHz differential voltage of 0.81. The corresponding +Pt amplitude for the 2.61 volt (estimated) NQI was 0.27 volts, while the maximum +Pt amplitude of 1.02 volts was associated with a NQI amplitude of 1.15 volts by bobbin in the mix channel. The range of bobbin to

+Pt amplitude ratios was 1.1 to 9.6 with an average of 3.48. The average bobbin amplitude (mix channel) for these SVI/NQI calls (not at TSPs) was 1.09 volts. The average +Pt voltage was 0.41 j volts. In general, these SVI/NQIindications not at TSP intersections had similar bobbin to +Pt j amplitude ratios, but had slightly larger individual channel amplitudes.

Several +Pt SVI calls were associated with dings or dents. The maximum +Pt amplitude for these I

C:\ TEMP \TGX 1RE08 CMoA FINAL Rev3 Non-prop. doc 27 l

d

F 1

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I SG-99-04-005 Revisl2n 3 l indications was 0.28 volts, while the ratio of bobbin (mix) to +Pt amplitudes ranged from 9.39 to 29.82 with an average of 16.84. Based on data developed during the bobbin qualification for dings, the minimum +Pt voltage reported for detected axial ODSCC was about 0.6 volts. Therefore, it can j be inferred from this data that if the SVI calls represent true degradation, this degradation poses no '

challenge to stmetural or leakage integrity, and such indications would not be expected to contribute to primary to secondary leakage during SLB conditions. For the SVIs at TSPs and in the freespan which were associated with dings or dents, no DNI call was made, suggesting that if ODSCC were present, it was below the detection threshold. One of these had a bobbin amplitude > 5 volts and was inspected as part of the ding ODSCC program. The others, as well as R40 C74 SG C, which had no associated bobbin call, were inspected during the traverse of the +Pt probe from a known structure to a freespan indication to be inspected, i The bobbin /+Pt voltage relationship was also investigated for VOL calls. VOL calls at STP are E I typically MBMs (which exist in the baseline) or AVB or baffle wear indications that were RPC inspected at one point in time and therefore included in the STP indication database. The +Pt voltage  !

of these indications was generally much larger than the SVI calls. Bobbin voltages were also much larger. With MBMs, shallow (< 5% TW) OD surface abrasions may be developed during removal of surface defects. The dissimilarity of +Pt and bobbin voltages between SVI/NQI and VOUMBM indications suggest that the SVI calls are not representative of MBMs, volumetric wall loss which may be associated with MBMs, or true volunietric wall loss, such as thinning or wear.

Finally, the majority of the SVI calls at TSPs were reported at cold leg intersections. The axial ,

ODSCC at TSP intersections at STP is almost entirely confined to the lower hot leg TSP intersections. If these SVI/NQI indications are early indications of a new damage mechanism, such as IGA or cellular corrosion, which are driven by chemistry and temperature conditions, the incidence would be expected to be predominantly restricted to the lower hot leg TSPs.

In conclusion, if these SVI/NQI indications at TSP intersections are representative of true degradation, they may be closely spaced patches of axial ODSCC with no associated structural or leakage integrity implications. Alternatively, these indications may be associated with low level

(<0.75 volt by bobbin) dings / dents or possibly attributed to sludge / scale accumulation or non-invasive, particulate type foreign material. As the true nature of these signals cannot be determined, they are not included in the EOC projections as part of the voltage based repair criteria for axial ODSCC at TSP intersections per GL 95-05. Based on the observations provided above, it is unlikely that these SVI/NQI signals at TSP intersections represent a new damage mechanism.

I I

l CATEMPiTGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 28

SG-99-04-005 Revision 3 l

STP Unit 1; 1RE08 Inspection '

SVl / NQI Data Analysis (values in italic are the SVis at TSPs)

SG D

+Pt Bobbin Bobbin /+Pt Amplitude Ratio Row Col Call Volts Elev. Call Volts Channel (Mix channel basis) 2 46 SVI 0.38 14C -0.3 NOI 0.69 P1(Mix) 1.82 7 49 .SVI 0.15 14C -0.37 NOI 0.65 P1 4.33 18 84 SVI 0.2 2H +8.41 DNG 2.25 P1 11.3 -

SG C

+ Pt Bobbin Row Col Call Volts Call Volts Channel 37 43 SVI 0.28 14C +0.33 DNT 2.63 P1 9.39 l 39 88 SVI 0.17 17C +1.57 DNG 5.07 P1 29.82 40 74 SVI 0.27 18C +0.47 NO DATA 47 75 SVI 0.27 22C +1.13 NOl 0.87 5 (130kHz 9.67 Diff)

SG B t

+ Pt Bobbin Row Col Call Volts Call Volts Channel 1 14 SVI 0.69 14C -0.37 NQI 0.8 P1 1.16 2 21 SVi 0.15 15C +42.07 NQi 0.22 5 4.4

16 65 SVI 0.12 6H +40.85 NOI 0.18 5 4.5 I 28 29 SVI 0.71 12C +3.7 NQ1 0.39 5 1.65 35 28- SVI 1.02 17C +14.41 NOl 0.35 5 1.03 36 22 SVI 0.34 15C +10.52 NOl 0.26 5 2.29 l 38 24 SVi 0.37 6H +23.03 NOl 0.51 5 4.14 38 44 SVI 0.43 5H +6.07 NOl 0.37 5 2.58 SG A

+Pt Bobbin Row Col Call Volts Call Volts Channel 3 29 SVI 0.1 14C -0.3 NOI 0.67 P1 6. 7 10 39 SVI 0.29 16C+34.42 NQt 0.32 P1 1.1 48 42 SVI 0.38 7H +0.29 NOI 0.52 P1 1.37 48 47 SVI 0.2 7H +0.35 NOI 0.38 P1 1.9 48 78 SVI 0.16 BH -0.33 NOI 0.45 P1 2.81 C:\TEMPiTGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 29

F i

l SG-99-04-005 Revision 3 l

l l

l SVis Reported at TSP Edge from Field Service Report SG D

+Pt Bobbin Row Col . Call Volts Elev. Call Volts Channel .

2 46 SVI 0.38 14C -0.3 NOl 0.69 P1 7 49 SVI 0.15 14C -0.37 NQ1 0.65 P1 SG C 37 43 SVI 0.28 14C +0.33 DNT 2.63 P1 40 74 SVI 0.27 18C +0.47 NO DATA SG B I

1 14 SVI 0.69 14C -0.37 NOl 0.8 P1 SG A l

3 29 SVI 0.1 14C -0.3 NOl 0.67 P1 48 42 SVI 0.38 7H +0.29 NQi 0.52 P1  ;

48 47 SVI 0.2 7H +0.35 NQ1 0.38 P1 1 48 78 SVI 0.16 8H -0.33 NOl 0.45 P1 l

l

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C:\ TEMP \TGX 1RE08 CMOA FINAL Rev3 Non-prop. doc 30

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