ML20078P898
| ML20078P898 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 07/31/1994 |
| From: | Esposito J WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML19311B572 | List: |
| References | |
| SG-94-07-009, SG-94-7-9, WCAP-14123, NUDOCS 9412210011 | |
| Download: ML20078P898 (200) | |
Text
{{#Wiki_filter:- .. __ . .- WESTINGHOUSE PROPRIETARY CLASS 3 ; WCAP-14123 SG-94-07-009 , BEAVER VALLEY UNIT 1 STEAM GENERATOR TUBE PLUGGING CRITERIA FOR INDICATIONS AT TUBE SUPPORT PLATES JULY 1994 Approved by: J.f ' . Esposito,)6anager '
- 4. t am Generator Technology & Engineering ,
i t i D WESTINGHOUSE ELECTRIC CORPORATION < NUCLEAR SERVICES DIVISION ! P. O. BOX 158 [ MADISON, PENNSYLVANIA 15663-0158 l t C 1994 Westinghouse Electric Corporation All Rights Reserved 9412210011 940729 PDR ADOCK 05000334 PDR
BEAVER VALLEY UNIT 1 STEAW GENERATOR TUBE PLUGGING CRITERIA FOR ;NDICATIONS AT TUBE SUPPORT PLATES TABLE OF CONTENTS SECTION PAGE 1 1.0 Introduction 1-1 2.0 Conclusions 2-1 3.0 Beaver Valley SG Pulled Tube Examinations 3-1 3.1 Introduction 3-1 3.2 Beaver Valley Tube Pull Results 3-1 l 3.3 Conclusions 3-6 4.0 Accident Condition Considerations 4-1 l i 4.1 General Considerations 4-1 j l 4-1 l 4.2 Allowable Leak Rate for Accident Conditions l l 5.0 Database Supporting Alternate Repair Criteria 5-1 5.1 EPRI ARC Database 5-1 5.2 NDE Uncertainties 5-3 i 6.0 Tube Burst and Leak Rate Correlations 6-1 l 6.1 EPRI ARC Correlations 61 l 6.2 Burst Pressure vs. Bobbin Voltage Correlation 6-2 6.3 Burst Pressure vs. Through Wall Crack Length Correlation 6-3 6.4 NRC Draft NUREG-1477 SLB Leak Rate POD 6-5 and Uncertainty Methodology 6.5 Probability of Leakage Correlations 6-6 ' 6.6 SLB Leak Rate versus Voltage Correlation for 7/8" Tubes 6-9 6.7 SLB Leak Rate Analysis Methodology 6-12 [ f 7.0 Beaver Valley Unit i SG Inspection Results 7-1 7.1 Inspection Results 7-1 3 7.2 Growth Rates From Prior Cycles 7-3 7.3 Growth Rates for Cycle 9 (1991 -1993) 7-5 7.4 Voltage Distributions for Example SLB Analyses 7-7 i
TABLE OF CONTENTS (continued) SECTION PAfd 8.0 Beaver Valley IPC Repair Criteria 8-1 8.1 General Approach to the IPC Assessment 81 8.2 IPC Repair Criteria for Beaver Valley Unit 1 82 l 8.3 Operating Leakage Limit 83 , 8.4 Example SLB Analyses 84 9.0 References 9-1 Appendix A NDE Data Acquisition and Analysis Guidelines A-1 ii
1.0 INTRODUCTION
This report provides the technical basis for tube plugging criteria for outside diameter stress corrosion cracking (ODSCC) at tube support plate (TSP) intersections in the Beaver Valley Unit 1 steam generators (SGs). The recommended plugging criteria are based upon bobbin coil inspection voltage amplitude, which is correlated with tube burst capability and leakage potential. The interim plugging criteria (IPC) for a repair limit of 1.0 or 2.0 volts are technically justified herein, consistent with the IPC methodology approved by the NRC for Farley-l and D. C. Cook-1 in the Spring of 1994. Additionally, the margins associated with a 1.0 volt IPC as defined by draft NUREG-1477 are also delineated in the following sections of this report. The criteria provide significant margins when compared to the guidelines of Regulatory Guide (R.G.) 1.121. The detailed justification that supports the implementation of an IPC at Beaver Valley Unit I utilizes NRC approved criteria in order to minimize the need for review of new materirJ, including inspection requirements. The only change in methodology from the Farley-1 and D. C. Cook-1 SERs for the 2.0 volt repair limit is the recommendation that the EPRI database (Reference 3) and the associated EPRI steam line break (SLB) leak rate versus voltage correlation be applied for the Beaver Valley-1 IPC. In addition, the Beaver Valley-1 allowable SLB leak rate utilizes thyroid dose conversion factors from ICRP-30, consistent with thra approved for the Braidwood-l IPC, whereas the Farley-1 and D.C. Cook-1 allowable leak rates were based on ICRP 2. If ongoing NRC reviews of other EPRI and plan' specific submittals lead to changes in the recommended methods or data, it is proposed to implement the NRC approved methodology at the time of the Beaver Valley-1 IPC approval. An example of this resolution could include the probability of detection (POD), for.which draft NUREG-1477 applies a value of 0.6 independent of voltage. Example SLB leak rate and burst probability analyses are included in this report and include SLB leak rates calculated with the EPRI leak rate correlation and draft NUREG-1477 methods. It is shown that the EPRI database is conservative for draft NUREG-1477 leak rate applications. The example SLB analyses are performed for Cycle 10 assuming a 1.0 or 2.0 volt IPC had been implemented and for the actual Cycle 10 indications left in service based on the 40% depth repair criteria applied for Cycle 10. The tube plugging criteria are based upon the conservative assumptions that the tube to TSP crevices are open (negligible crevice deposits or TSP corrosion) and that the TSPs are displaced under accident conditions. The ODSCC existing within the TSPs is thus assumed to be free span degradation under accident conditions and the principal requirement for tube plugging considerations is to provide margins against tube burst in accordance with R.G.1.121. He open crevice assumption leads to maximum leak rates compared to packed crevices and also maximizes the potential for TSP displacements under accident conditions. Laboratory testing of incipient denting or dented tube intersections shows no leakage or very small leaksge, such that leakage even under steam line break (SLB) conditions would be negligible. Implementation of the tube plugging criteria is supplemented by 100% bobbin coil inspection requirements at TSP elevations having ODSCC indications, reduced operating leakage 1-1
1 l requirements, inspction guidelines to provide consistency in,the voltage normalization, and ; rotating pancake coil (RPC) inspection requirements for the larger indications left in service to . 1 characterin the principal degradation mechanism as ODSCC. In addition, it is required that potential SLB leakage be calculated for tubes with indications at TSPs left in service to demonstrate that the cumulative leakage is less than allowable limits. ! Two hot leg tubes with a total of six TSP intersections were pulled from Beaver Valley Unit 1 in 1991. Both non-destructive and destructive examinations were performed on all but one of the intersections, to characterize corrosion at the TSP crevice locations. Room temperature leak and burst testing were conducted on three TSP regions which exhibited OD indications with the bobbin probe, to supplement the existing EPRI database for attemate repair criteria. The crack morphology and test results for the Beaver Valley-1 pulled tube indications are l consistent with the EPRI database for ODSCC at TSP intersections.
- This report provides the technical bases for interim repair criteria for tubes with ODSCC at TSPs, using the database and methodologies developed in EPRI documentation (References 1 i to 3) and NRC approved SERs. The following activities have been performed as documented !
in this report: i
- Sumniary of Beaver Valley Unit 1 pulled tube examinations - Section 3 ;
- Discussion of accident condition considerations and determination of the plant specific ]
allowable leak rate for accident conditions - Section 4 3 i e Review of the existing EPRI documentation supporting alternate repair criteria (ARC), ) including the EPRI ARC database and documentation outlining criteria for inclnsion or ; J exclusion of data from the leak / burst correlations, and development of NDE uncertainties - Section 5
- Development of tube burst and leak rate correlations - Section 6
- Review of past Beaver Valley Unit 1 SG inspection results, and development of Beaver Valley-1 bobbin voltage growth rates - Section 7 i
- Integration of the inspection and leak / burst test results to define the Beaver Valley 1 !
interim plugging criteria - Section 8 ! i
- The eddy current inspection and analysis guidelines that will be used upon implementation f of the IPC are provided - Appendix A j l
The overall summary and conclusions for this report are described in Section 2. [ t i t i i 4 1-2 . i
.m - . ._.-- ~ - - _ _ _ _ _ _ _ _ .. . . _ . - _ _ . . _ _ . . _ . _ _ . _
2.0 CONCLUSION
S This report documents the technical support for interim plugging criteria (IPC) with a 1.0 or 2.0 volt repair limit for ODSCC indications at the steam generator TSPs of Beaver Valley Unit 1. The Beaver Valley IPC follow the criteria of NRC issued SERs for 2.0 volt repair limits implemented at Farley-1 and D. C. Cook-1 in order to minimize NRC review time, with the following exceptions. It is recommended that the EPRI database of Reference 3 be used, that the associated EPRI SLB leak rate versus voltage correlation be applied for leak rate analyses and that the allowable SLB leak rate utilizes thyroid dose conversion factors from ICRP-30, consistent with the Braidwood-l IPC. Additionally, the margins associated with a 1.0 volt IPC developed in accordance with draft NUREG-1477 are detailed herein. Characterization of degradation at TSP intersections from two tubes at Beaver Valley-1 supports ODSCC as the dominant corrosion mechanism, consistent with the EPRI database. j The EPRI database includes the Beaver Valley-1 pulled tube data. The NRC review of the EPRI outlier evaluation of Reference 3 has not yet been completed. It is recommended that the NRC review be completed in time to support implementation at Beaver Valley-l. The EPRI database is applied for all analyses in this report. Burst pressure, probability of leakage and SLB leak rate versus voltage correlations are given based on the EPRI database. Even if { j the draft NUREG-1477 (Reference 6) leak rate methods were applied,it is shown that the j EPRI database is more conservative than the database recommended by the NRC in the i l Farley-1 and D. C. Cook-1 SERs. With the exception of the EPRI database and leak rate correlations, the proposed IPC for Beaver Valley-1 follows the guidelines of the Farley-1 and D. C. Cook-1 SERs. Both the 1.0 and 2.0 volt IPC repair limits provide significant margins against Regulatory Guide 1.121 guidelines for structural limits. Since the R.G.1.121 guideline for a three times normal operating pressure differential is satisfied by the TSP constraint at normal operating limits, the required structural limit is to satisfy a margin of 1.43 times the SLB pressure differential. For a lower 95% prediction interval and lower tolerance limit material properties on the burst pressure versus voltage correlation, the structural limit for 1.43 APst3 is 8.82 volts. A full APC repair limit would then be 5.5 volts based on reducing the 8.82 volt structural limit by allowances of 20.5% for NDE uncertainties and 40% for voltage growth. Thus a 1.0 volt repair limit provides a margin of 4.5 volts against the full APC repair limit, while a 2.0 volt repair limit provides a margin of 3.5 volts. He Farley-1 and D. C. Cook-1 IPCs conservatively applied 3.6 volts for the full APC repair limit. Since the Beaver Valley-1 IPC follows this precedence, the 3.6 volt limit is also applied for the Beaver Valley-1 APC repair limit. The allowable limit for SLB leakage using guidelines of the NRC Standard Review Plan with ICRP 30 thyroid dose conversion factors (see Section 4.2)is 6.6 gpm for the faulted loop. To demonstrate that acceptable SLB leak rates and tube burst probabilities can be expected for Cycle 11 with an IPC of 1.0 or 2.0 volts for Beaver Valley-1, example SLB analyses were performed for Cycle 10 assuming that a 1.0 and 2.0 volt IPC was implemented for this cycle. ( Applying the recommended analysis methods using the EPRI database and correlations with a l voltage distribution adjusted by a probability of detection (POD) of 0.6 (draft NUREG-1477 2-1
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guidance), the projected EOC-10 SLB leak rate is 0.044 gpm and the tube burst probability is estimated at 6.3x10" for the 2.0 volt repair limit.' These results are much lower than the allowable leak limit of 6.6 gpm and all,owable burst probability guideline of 2.5x10 2 Even if draft NUREG-1477 leak rate methods are applied, the projected SLB leak rate of 0.46 gpm is much less than the allowable 6.6 gpm limit. Thus,it can be expected that application of a 2.0 volt IPC repair limit for Cycle 11 would result in acceptable potential leakage and burst probability. A decrease in SLB leakage of 5% and a decrease in burst probability of approximately.15% will result with a 1.0 volt repair limit, compared to the corresponding values with a 2.0 volt repair limit. SLB analyses were also performed for the actual Cycle 10 indications left in service which were based on application of the 40% depth repair limit. It is shown that SLB leakage and burst probabilities for the 40% depth repair limit are only about 15% and 25% lower, respectively, than the results for the assumed IPC of 2.0 volts. Thus, application of a 1.0 or 2.0 volt repair limit at Beaver Valley-1 does not significantly increase the potential leakage or burst probability compared to a 40% depth repair limit. SLB leak rate sensitivity analyses, using draft NUREG-1477 methodology, were also performed for the NRC recommended database and for all six forms of the probability of leakage (POL) correlation discussed in draft NUREG-1477. The results show that the NRC database for draft NUREG methods yields SLB leak rates a few percent lower than obtained with the EPRI database. Although only the EPRI recommended log logistic and the log normal forms of the POL correlation are considered to adequately represent the data, SLB leak rate sensitivity analyses were performed for all six POL forms. For the Beaver Valley-1 analyse, the log logistic POL yields about 30% higher leak rates than the log normal form for draft NUREG methods and a few percent higher leak rates for the EPRI leak rate correlation. These differences are small variations about leak rates much less than allowable limits. The other four forms of the POL correlation yield leak rates up to a factor of 8 higher than the log logistic for draft NUREG-1477 methods and up to a factor of almost 4 higher for the EPRI leak rate correlation. The highest leak rate of 3.57 gpm for a 2.0 volt IPC (3.43 gpm for a 1 volt IPC,2.96 gpm for a 40% depth limit) results for the linear Cauchy POL form which has the greatest differences from experimental POL data. The Cauchy distribution has about a 3% POL down to zero volts while no indications below 1.0 volt have been found to leak and no undetected indications have been found by destructive exam to have crack depths greater than about 65%. Since the log logistic and log normal POL forms yield comparable leak rates and the other forms differ significantly from leakage trends, it is adequate to evaluate SLB leakage with the log logistic POL and analyses with the other forms are not warranted. In either case, all estimated SLB leak rates based on Cycle 10 data yield projected EOC leak rates less than the allowable 6.6 gpm. SLB tube burst probability analyses were also performed using both the EPRI and NRC databases. For the burst pressure correlation, the EPRI outlier evaluation has recommended exclusion of identified data having much higher burst pressures at their respective voltages than the remaining database. EPRI criteria (Reference 3) for evaluation of outlier data lead to exclusion of the identified high burst pressure data on the basis of quantifiable differences in crack morphology from the remaining database. As noted, the EPRI database is recommended for the Beaver Valley-1 IPC. The NRC review of the EPRI outlier evaluation has not been completed at this time and completion of the review is recommended for the 2-2 1
Beaver Valley-1 IPC. Since the high burst pressure outliers are include'd in the current NRC recommended database, uncertainties in the burst pressure correlation are higher for the NRC database and this results in higher tube burst probabilities than obtained for the EPRI database. The estimated SLB tube burst probabilities for a 2.0 volt IPC,1.0 volt IPC and 40% depth limits (voltage distributions with a POD = 0.6 adjustment) are 6.3,5.5 and 4.7 x 10" for the EPRI database and 1.4,1.2 and 1.0 x 10-2 for the NRC database. These burst probabilities for the NRC database are considered to be excessively high and are not appropriate for IPC applications even though all values are less than the acceptance guideline of 2.5 x 10 2 found acceptable in NUREG-0844. Lntenm Plugninn Criteria (IEC) The justified IPC for Beaver Valley can be summarized as follows: . .
. Tube Plugginn Criteria Tubes with bobbin flaw indications exceeding a 1.0 or 2.0 volt IPC voltage repair limit and 5 3.6 volts are plugged or repaired if confirmed as flaw indications by RPC inspection. Bobbin flaw indications > 3.6 volts attributable to ODSCC are repaired or plugged independent of RPC confirmation.
- Operatine Leakane Limits Plant shutdown will be implemented if normal operating leakage exceeds 150 gpd per SG.
. S1_B_Lpakage Criterian Projected end of cycle SLB leak rates from tubes left in service, including a probability i of detec+ ion (POD) adjustment and allowances for NDE uncertainties and ODSCC growth rates, must be less than 6.6 gpm for the SG in the faulted loop. If necessary to satisfy the allowable leakage limit, additional indications less than the repair limit shall be plugged or repaired.
- T_nhg_Eurst Eal2_ahility The projected end of cycle SLB tube burst probability shall be calculated and compared with the value of 2.5 x 10 found acceptable in NUREG-0844.
- E x cl u sioris_ farnluj2.e. _ EluggiplQite_tia Indications excluded from application of the IPC repair limits include: indications found by inspection (bobbin or RPC) to extend outside the TSP, indications not attributable to ODSCC and circumferential indications. These indications shall be evaluated to the Technical Specification limits at 40% depth.
2-3
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faenection Requirements
. Eddy current analysis guidelines and voltage normalization consistent with that of Appendix A shall be implemented for the Beaver Valley-1 IPC applications.
- Eddy current analysts shall be trained specifically to voltage' sizing per the Appendix ~ A analysis guidelines, and at least lead analysts shall be qualified to the industry standard Qualified Data Analysis program of the EPRI ISI guidelines.
. Use of ASME calibration standards cross-calibrated to the reference laboratoiy standard
' and use of a probe wear standard requiring probe replacement at a voltage change of 15% from that found for the new probe shall be implemented per Appendix A.
. 100% bobbin coil inspection of all active tubes with a 0.720 inch diameter bobbin probe, for all hot leg TSP intersections and all cold leg intersections down to the lowest cold leg TSP where ODSCC indications have been identified.
. RPC inspection of all bobbin indications greater than 1.5 volts for a 2.0 volt repair limit, or greater than 1.0 volt for a 1.0 volt repair limit, shall be performed to confirm axial ODSCC as the dominant mechanism for indications at the TSPs.
. RPC sample inspection of at least 100 TSP intersections with dents or artifact / residual signals that could potentially mask a 1.0 or 2.0 volt bobbin signal, depending upon the repair limit specified in the plant's Technical Specification. The RPC sample program shall emphasize dented TSP intersections but include artifact signals that the . analysts judge could mask a repairable indication. Any RPC flaw indications in this sample will be plugged or repaired.
. The NRC will be informed, prior to plant restart from the refueling outage, of any unexpected inspection fmdings relative to the assumed characteristics of the flaws at the TSP intersections. This includes any detectable circumferential indications or detectable OD indications extending outside the, thickness of the TSP.
The RP.C inspection requirements for indications above 1.5 volts and for a minimum 100 intersection sample plan are consistent with the NRC resolution of draft NUREG-1477 issues as presented by the NRC at the NRC/ industry meeting of February 8,1994 on resolution of industry comments to the draft NUREG. These RPC inspection guidelines were presented by the NRC as part of the 2.0 volt IPC proposal. 2-4
3.0 BEAVER VALLEY SG PULLED TUBE EXAMINATIONS-3.1 Introduction Two tubes were removed from Beaver Valley 1 in 1991 and were examined to characterize corrosion at the tube support plate (TSP) crevice locations. The destructive examination was performed by ABB Combustion Engineering; this section provides a summary of the reported results. The first, second and third support plate crevice regions (TSP 1, TSP 2 and TSP 3) _ of each tube were removed,in addition to the tubesheet expansion transition region. The first TSP of each tube exhibited OD indications with the bobbin and RPC probes, while all but one of the remaining intersections were No Detectable Degradation (NDD) by both bobbin and RPC. Following non-destructive examination, room temperature leak testing and room temperature burst testing were conducted on the TSP regions. The burst tested specimens were then destructively examined using metallographic and Scanning Electron Microscope (SEM) fractography techniques. The following presents a brief summary of the more significant observations of the OD origin IGSCC. 3.2 Beaver Valley-1 Tube Pull Results Hot leg tubes RllC48 and R16C60 were pulled. In each case, the sections pulled included the first, second, and third tube support plate intersections and the tubesheet expansion transition. Pull forces were 800 lbs. or less during the removal of the tube sections containing the TSP intersections. Laboratory NDE, leak and burst testing, and destructive examinations were performed. The following summarizes the data obtained at each support plate region. 3.2.1 NDE Testing , Laboratory eddy current testing was performed using an A740SF/RM bobbin coil probe, Test frequencies were 400 kHz,200 kHz,100 kHz, and 10 kHz in differential and absolute modes. The probe speed was 12 in/sec. This probe was calibrated to provide a 4 volt response to a 20% ASME flaw at 400 kHz. The RPC probes were B 720 3 Coil MRPC, calibrated to a 5 volt response to 60% ASME flaws at 400 kHz. The RPC probe speed was 0.2 in/sec. Depths were calculated using a 3 point fit curve at 400 kHz. Testing was performed with and without a carbon steel collar utilized to simulate the tube support plate. The effect of the pull forces in potentially opening up cracks was not reported. 'Ihe relatively low pull forces would indicate that this effect was negligible, but, as reported later in this section, the tube pull was reported to have affected the UT testing. , The reported post-pull, laboratory bobbin coil voltages, angular extent, and estimated depths are shown in Table 3-1, along with similar data from RPC testing. Indications were observed at TSP 1 on both pulled tubes. With one exception, no degradation was observed by bobbin or RPC probes at TSPs 2 and 3. The bobbin coil indicated a very shallow indication (6%) at j the second TSP of R16C60, but the MRPC did not suggest the presence of degradation at this i location. l l 3-1
l The field eddy current inspection reported bobbin indications at 400/100 kHz of 2.70 and 1.29 volts for the 1st TSP of R16C60 and RllC48, respectively. The pompull laboratory indication at the 2nd TSP of R16C60 was not reported in the field. Laboratory reevaluation of the field data tapes performed by Westinghouse found bobbin indications of 2.84 volts, 0.9 volt and NDD for the first 3 TSP intersectiuns of R16C60 and indications of 1.4 volts and 0.2 volt for the 1st and 3rd TSP intersections of RllC48. The laboratory reevaluation voltages (of field data tapes) are used in the EPRI database for IPC/APC applications. As noted later, the 3rd TSP intersections of both tubes were found by destructive examination to have crack depths < 20% Comparisons of the field and post-pull laboratory voltages indicate that only the 1st TSP intersection of RllC48 had an in0uence of the tube pull on the voltage, with the indication increasing from about 1.4 volts in the field to 2.5 volts in the post pull laboratory examination. Ultrasonic testing (UT) was also performed on the samples. UT signals were noisy, as some of the deformation incurred during the tube removal process apparently hampered correct centering of the probe in the tube. Characterization and sizing of defects could not be done accurately. Indications were reported up to 0.2 inch long and 26% deep on RllC48 at the first tube support plate intersection. On R16C60, small crack-like indications 0.1 inch long and 24% and 22% deep were reported at the first and third TSP intersections, respectively. Radiography did not produce any observable indications. Visual observation of the tube sections was performed with the unaided eye and with a stereomicroscope with magnifications of up to 40X. Relatively heavy deposits were reported, and metallic copper was observed in the deposits at the TSP locations. At no locations were there any indications visible. < The inside diameter of each tube section was measured using a three point intra-micrometer. As expected from the NDE data, no denting was observed by these measurements. 3.2.2 Leak and Burst Testing Following NDE characterization, three tube support plate intersections were leak and burst tested. These included
- R16C60 TSP 1, which post pull laboratory ECT indicated had an 18% throughwall crack at 400 kHz and 49% at 400/100 kHz.
- R16C60 TSP 2, which post pull laboratory ECT indicated had a 6% throughwall crackat 400 kHz and 7% at 400/100 kHz.
- RllC48 TSP 1, which post-pull laboratory ECT indicated had a 37% throughwall crack at 400 kHz and 57% at 400/100 kHz.
Burst testing was performed by sealing each end of the tube with mechanical fittings, the upper one of which was connected to 1/8-inch high pressure tubing to permit pressurization of 3-2
1 the sample. Some of the fittings leaked initially and were sealed by silser soldering. The l pressurizing equipment included: a) a hand pump to pump deionized water to pressurize the specimens b) a calibrated pressure gage - l c) a pressure transducer connected to a strip chart recorder d) 1/8-inch high pressure tubing e) a 3000 psi accumulator with valve. . The tests were initially conducted without an intemal bladder to determine at what pressure leakage occurred. If a burst was not obtained, the test was interrupted, a bladder was inserted, and the test resumed until a burst, as indicated by a " fish mouth" opening, occurred. A bladder was required in only one case. All failures were axially oriented. l Tube RilC48 TSP 1 was burst test with a thick carbon' steel collar to simulate support by the tube support plate. This technique was not employed in the remaining two TSP burst tests, as the presence of the collar provided support to the tube in the area with degradation, such that bursting occurred in the non-degraded portion of the tube outside the TSP at 11,500 psig. Tube section R16C60 TSP 1 was prepared for burst testing without using the carbon steel support ring. No fitting leaks were observed, and this section exhibited a final burst pressure of 9,350 psig. Tube section R16C60 TSP 2 was also burst without the use of the carbon steel collar. This section burst at a pressure of 10,200 psig. l 3.2.3 Characterization of the Corrosion Cracks Cracks were examined by a number of techniques including light microscopy, fractography and are reported in this section. Auger emission spectroscopy /X-ray photoelectron spectroscopy of the cracks, base metal characterization, and chemical analysis of tube surface deposits were also performed, but have not been reported here, since they do not directly bear upon crack morphology. Areas in which indications were observed by NDE or visual examination were examined by cross sectional metallography to characterize the type and extent of corrosion and to determine crack morphology. The areas containing the crack were cut so that longitudinal and transverse' sections could be prepared. The samples were mounted, polished, etched, and examined using conventional metallographic techniques. A dual etching process was performed on longitudinal sections using electrolytic nital and ortho-phosphoric acid. Glyceregia and nital were used as etchants on the transverse sections. For the burst samples (R16C60 TSP 1 and R16C60 TSP 2), three transverse samples were cut from the upper, mid-plane and lower portion of the " fishmouth" of the burst. For RllCG TSP 1, three transverse samples were cut from the upper, mid-plane and lower portion of the tube support plate intersection. The sections of tube from the third TSP intersection, R16C60 TSP 3 and RllC48 TSP 3, were examined at the mid-section of the intersection only. No light metallography data were reported for RllC48 TSP 2. 3-3
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Longitudinal sections were prepared of all six tube support plate intersections with the exception of RllC48 TSP 2. All mounts were prepared following ASTM procedures. Photomontages of all mid plane TSP regions as well as top of TSP and bottom of TSP regions for selected tubes were constructed from the burst test transverse sections. Depth of penetration measurements around the circumference of the mid-TSP mounts were taken for each crack directly from the transverse photomontages for which the magnifications were known. Each crack was identified, and its depth determined with a filar eyepiece. The mean crack depth was calculated and reported._ The tube circumference was divided into ten-degree sectors and the maximum penetration within each sector was plotted as a function of angular position. Tube _R16C60 ISP_1 Figure 3-1 is a transverse view of axial cracks near the top of the tube support pla'.e region of the tube. Glyceregia was utilized as an etchant to show the presence of any poteatial IGA. After etching the transverse mount, there were only small patches of shallow naf ergranular attack (IGA) observed in isolated areas along the tube OD. The indications of IGA were between one and four grains deep. Many large OD-initiated indications of intergranular stress corrosion cracking (IGSCC) were present along the entire circumference of the sample. The glyceregia etchant was not used on the remaining transverse sections cut from this tube, since negligible IGA appeared. From the photomontages for this sample,160 distinct crack-like indications were reported along the circumference of the sample. The average of the axial crack depths was 33% and the maximum depth 53%. The crack depth information for this and all other tube support plate intersections is shown in Table 3 2. Figure 3-2 illustrates the maximum penetration' " (reported as percent throughwall) of the multiple axial indications at ten-degree increments of the circumference for the mid-TSP section as a function of angular position. The 100% depth in Figure 3-2 corresponds to the burst opening. A transverse view of axial cracks at the mid-plane of the tube support plate region is shown in Figure 3-3. This metallographic mount was etched using electrolytic nital. Several cases of IGSCC were observed in the mid-plane region, as can be seen in the 200X photographs. Refer to Table 3-2 for crack depth information. A third transverse metallographic mouu was prepared from the bottom of the TSP region. This mount was also etched in electrolytic n,tal, but did not show signi6 cant degradation as seen in the upper and mid-plane regions of the TSP. There were no cases of crack-like : indications found on this mount. Figure 3-4 includes both high (200X) and low (50X) magnification views of this transverse section. , Tuhn R16C60 TSP 2 Transverse tube sections were cut from R16C60 TSP 2 at the top, mid-plane and bottom of the tube support plate region of the tube section. In the top of the support plate region, there was a small number of cracks visible at 200X magnification. Figure 3-5 shows 3-4
photomicrographs at 50X and 200X which show the appearance of the transverse section cut from the top of the TSP region, etched with nital. Figure 3-6 show the mid-plane transverse TSP section of the tube after a glyceregia etch. Several large indications ofIGSCC were found along with small patches of shallow IGA, as seen in the 200X photographs. Figure 3-7 shows the maximum penetration (reported as percent throughwall) at ten-degree incremer,ts of the circumference for the mid-TSP region as a function of angular, position. This figure illustrates the burst loccfon at about 200*. A third transverse metallographic mount was prepared from the bottom of the TSP region. This mount was also etched with electrolytic nital. There was no evidence of cracking in the transverse sample taken from the bottom of the tube support plate. Tube B16C60 TSP 1 . . . . Minor cracking (less than 20% depth) was observed at in the transverse section at the mid-plane of this intersection. No photomicrographs are presented. Tube R11C48 TSP 1 After bursting of this specimen with the carbon steel collar in place, the carbon steel support ring was removed from the TSP region. Three transverse mounts were prepared from the tube support plate region of the sample. The top of the support plate region showed only minor degradation due to cracking, as shown in Figure 3-8. The mid-plane section of this sample showed the greatest extent of IGSCC. Several micrographs of typical examples of cracks found on the OD of this tube are shown in j Figure 3-9. Crack depth is again shown in Table 3-2. The trsnsverse tube section cut from the bottom of the TSP section, like the top of the TSP section, showed minor degradation due to IGSCC. Some examples of cracks are presented in Figure 3-10. Iuhg_R11C48 ISP_1 Minor cracking (less than 20% depth) was observed in the transverse section at the mid-plane I of this intersection. No photomicrographs are presented. Fractonraphy Upon completion of burst testing, a section was removed from two of the TSP intersection burst test specimens (R16C60 TSP 2 and R16C60 TSP 1) for analysis by scanning electron microscope (SEM). Section RllC48 TSP 1 was not examined using SEM since the high . I burst pressure and location of tube rupture indicated the tube experienced ductile failure. SEM surface examinations were supplemented with energy dispersive spectrometry (EDS) to determine if any contaminants were present on the crack surface. All fractography was 3-5
performed on one of two axial burst crack faces. SEM/EDS was performed on two TSP region sections which had not been subjected to burst testing. Selected areas were examined in detail to determine crack morphology, followed by documentation with photomicrographs at 30X or 40X. SEM montages were prepared and compared to the low magnification photographs where the tube support plate location was clearly observable. Identifiable pattems on both the high and low magnification photographs were used to obtain length ratios between the high and low magnification photographs. These ratios were used to compare the crack length to the TSP width and the position of the crack relative to the top of the TSP. With this method,it was also possible to correct the burst crack lengths to the pre-deformation lengths. The method further indicated that the burst cracks for samples R16C60 TSP 2 and R16C60 TSP 1 were contained within the axial extent (thickness) of the tube support plate. No cracking extended beyond the TSP regions in these two samples. B16C60 IEE_1 A 40X photomontage of the tube section at this intersection was prepared. Table 3-3 illustrates the data from the SEM montages. There were no obvious areas of fatigue, transgranular cracks, etc. There were approximately sixteen ligament-like features present on the fracture surface, oriented in the radial direction. These ligaments represent the material connecting the tips of adjacent and overlapping cracks. Most of the ligaments appeared to have failed in a ductile mode when the sample was burst. R16C60 ISP_2 A 40X photomontage of this fracture surface was constructed to study the extent of tube degradation at the fracture surface. EDS analysis of this sample showed silicon, which was hypothesized to be contamination from the cutting wheel used to section the tube, and alloy materials. Minor indications of magnesium were also identified on the fracture surface. EDS analysis of the OD deposits identified iron, nickel, chromium, calcium, titanium, lead, aluminum, and potassium. Table 3-4 presents the crack depth and ligament data from the SEM montage. 3.3 Conclusions The field evaluation, laboratory reevaluation of the field data and the post-pull laboratory eddy current inspections accurately described the presence of axial cracking at the first TSP intersection of each pulled tube. TSP 1 of R16C60 exhibited a 49% (400/100 kHz mix without support ring, Table 3-1) throughwall crack, while TSP 1 of RI1C48 exhibited a 57% throughwall crack. No field degradation was reported by bobbin or RPC probes at TSPs 2 and 3. However, the average depth for the 2nd TSP of R16C60 had an average crack depth < 40% and the maximum depth found by destructive exam at the 3rd TSP intersections was < 20%. Thus the indications not reported in the field would have had no significant impact on tube integrity. The 2nd TSP indication on R16C60 was found by both laboratory reevaluation 3-6
of the field data and by post-pull laboratory inspection. UT signals were noisy, as some of the deformation incurred during the tube removal process apparently hampered correct centering of the probe in the tube. UT indications were reported up to 0.2 inch long and 26% =- deep on RllC48 at the first tube support plate intersection. On R16C60, small crack-like indications 0.1 inch long and 24% and 22% deep were reported at the first and third TSP intersections, respectively. The three tube support plate intersections with EC indications were leak and burst tested. Tube R11C48 TSP 1 was burst test with a thick carbon steel collar to simulate support by the tube support plate. The presence of the collar provided support to the tube in the area with degradation, such that bursting occurred in the non-degraded portion of the tube at 11,500 - psig. Tube R16C60 TSP 1 and TSP 2 were burst tested without the carbon steel support ring. and exhibited burst pressures of 9,350 psig and 10,200 psig, respm rely. Metallographic and fractographic examination of R16C60 TSPs 1 and 2 showed axial cracks near the top edges of both TSP regions, as well as in the mid-plane regions of the TSP crevices. Several large OD-initiated indications of IGSCC were present in both intersections, along with small patches of IGA. No crack-like indications were observed at the bottom of either TSP intersection. On RllC48 TSP 1, only minor cracking was observed at the top edge of the TSP, the mid-plane of this sample showed the greatest extent ofIGSCC. Minor degradation due to IGSCC was also observed at the bottom edge TSP 1 on RllC48. The remaining intersections not burst tested exhibited minor cracking (<20% depth) in transverse sections at the mid-plane of the TSP intersection. In conclusion, the destructive examination of two pulled tubes from Beaver Valley 1 confirmed the presence of primarily axially-oriented OD-initiated stress corrosion cracks. The cracks were confined to the tube support locations and did not extend beyond the upper and lower boundaries of the tube support plates. The cracks were generally short (<0.2 inch) l microcracks and were separated by thin ligaments of non-corroded material that provided
- some structural support. The macrocrack corrosion lengths for the burst cracks of RllC60 at the first and second TSPs were 0.73" and 0.74" There were no indications of transgranular cracking nor were there any indications of crack extension outside the TSP during service at any location.
- The examination results support the conclusion that the Beaver Valley 1 TSP indications are consistent with the database accumulated from other plants for ODSCC at TSP intersections.
Burst pressure results for tube R16C60 are close to the mean of the APC burst pressure versus bobbin voltage correlation. The crack morphology of OD IGSCC with small patches of IGA is typical of the pulled tube data for TSP crevice regions. me 3-7
l Table 31 1991 Beaver Valley 1 Tube Pull Eram Bobbin Coll and RPC Voltages - Imboratory Results With Support Ring Without Support Ring Tjf 400 kHz Diff. 400/100 klig 400 kHz Diff._ 400/100 kHz ! Iuhg Bobbin Coil 2.50V 2.48V 2.16V RI1C48 1 3.8 V 102 Deg. 129 Deg. 97 Deg. 70 Deg. 52 % 37% $7% 81 % 2.75V 4.58V 2.97V R16C60 1 3.58 V 107 Deg. 151 Deg. 106 Deg. 153 Deg. 48% 18 % 49% 16% NDD* 2.12V 1.29V R16C60 2 NDD* 107 Deg. 164 Deg. 146 Deg. 153 Deg. 48% 6% 7% 16% RF{ 1.33V 0.82V 1.35V RllC48 1 0.84 V 75 Deg. 112 Deg. 81 Deg. 113 Deg. 31% 31% 0% 28% 1.08V 1.28V 1.28V R16C60 1 0.92V 94 Deg. 149 Deg. 113 Deg. 145 Deg. 16% 5% 0% 0%
*NDD: No Detectable Degradation All other tube support plate intersections of the pulled tubes were NDD.
I 3-8
k Table 3 2 1991 Beaver VaBey 1 Tube Pull Exam Tube Support Plate Crack Data Number Maximum Average Ighn TSP
- nf_ Cracks Penetration Crack Dfalh ,
R16C60 1M 70 33 % 20% i R16C60 IT 160 53 % 33 % R16C60 2M 53 48% 30% RllC48 IM 39 54 % 40% RllC48 IB 6 38% 22% Designation of T, M and B signifies Top of TSP, Mid-plane of TSP, and Bottom of TSP, respectively. ; i l i i f 3-9
Table 3-3 1991 Beaver Valley 1 Tube Pull Fr== 1 SEM Measmtments fkm R16C60 TSP 1 l l l Ligament to Maximmn Ligament Crack # Linament Distance Qask. Depth Length (mils) (%) (mils) 1 25.00 10.0 12.5 I 2 51.25 22.5 12.5 l i 3 57.50 40.0 15.6 , 4 20.00 33.5 21.9 5 60.33 46.0 28.1 l 6 55.00 65.0 34.4 7 41,25 67.5 34.4 8 67.50 62.5 23.4 , 9 26.25 42.5 25.0 10 31.25 56.3 26.6 11 37.50 50.0 25.0 12 25.00 50.0 25.0 13 67.50 52.5 20.3 14 55.00 30.0 10.9 r 15 15.00 20.0 12.5 16 65.00 30.0 -- Average Crack Depth = 41% Burst Crack, Length = 0.77 inches Corrected Crack Length = 0.73 inches l 3 - 10 ; i 1
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b Table 3-4 1991 Beaver Valley 1 Tube Pull Exam l SEM Measurements from R16C60 TSP 2 Ligament to Maximum Ligament : Crack e Ligament Distance Crack Depth Lenath (mils) (%) (mils) i 1 120.0 32.5 12.5 ! 2 27.5 35.0 15.6 - 3 36.25 37.5 21.9 4 50.0 50.0 23.4 5 217.5 52.5 21.9 6 137.5 50.0 17.2 7 60.0 47.5 21.9 8 95.0 40.0 18.8 9 57.5 , 32.5 9.4 10 68.75 20.0 -- l l Average Crack Depth = 36% . Burst Crack Length = 0.92 inches Corrected Crack Length = 0.74 inches , i i 3 - 11
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r l l l 4.0 ACCIDENT CONDITION CONSIDERATIONS 4.1 General Considerations for Accident Condition Analyses Smam line break and combined accident analyses for the Beaver Valley Unit 1 SGs have been documented in WCAP-13579 (Reference 4) and are consistent with the methodology used in WCAP-12871 (Reference 5), with the exception of the use of ICRP-30 for thyroid dose conversion factors in the evaluation to determine the allowable SLB leak rate. The analyses . included: TSP displacements in a SLB cvent, combined LOCA+SSE loadings for potential tube deformation assessments, and the effects of combined SSE+FLB/SLB stress levels on tube burst capability; these structural analyses are not repeated in this repon. Both References 4 and 5 conclude that no tubes need to be excluded from application of the APC/IPC for reasons of defonnation resulting from combined LOCA+SSE loadings. For tube burst considerations, all indications are assumed to be free span indications consistent with the EPRI ARC criteria. "Ihis assumes that TSP displacements in a SLB event are large enough to expose most or all of the ODSCC cracks formed within the TSP crevices at normal operating conditions, which is very conservative for most tube locations. The allowable leakage in a SLB event is plant specific and is developed for Beaver Valley Unit 1 in Section 4.2, below. This evaluation supersedes that presented in Section 11.3 of WCAP-13579 (Reference 4), as it includes the use of ICRP-30 for thyroid dose conversion factors in determining the allowable leak rate for accident conditions. 4.2 Allowable Leak Rate for Accident Conditions An evaluation has been performed to determine the m'aximum permissible steam generator primary to secondary leak rate during a steam line break for the Beaver Valley Unit 1 Nuclear Station. The initital evaluation of WCAP-13579 considered both pre-accident and accident initiated iodine spikes, with thyroid dose convession factors based on Reg. Guide 1.109. The results of the evaluation, presented in Section 11.3 of WCAP-13579, showed that the accident initiated spike yields the limiting leak rate. Therefore,in determining the allowable le3k rate for this report using thyroid dose conversion factors based on ICRP-30, only the accident initiated iodine spike case was evaluated. This case was based on a 30 rem thyroid dose at the site boundary (SB) and initial primary and secondary coolant iodine activity levels of 1 pCi/gm and 0.1 pCi/gm dose equivalent (DE)I-131, respectively. A leak rate of 6.6 gpm was determined to be the upper limit for allowable primary to secondary leakage in the SG in the faulted loop. The SG in each of the two intact loops was assumed to leak at a rate of 150 gpd (approximately 0.1 gpm), which is the proposed Technical Specification LCO for implementation of IPC. The allowable leak rate will increase in inverse proportion to a reduction in the primary and secondary equilibrium coolant activity. For example, the allowable leak rate will increase to approximately 18 gpm if both prima.y- and secondary allowable coolant activity levels are reduced to 0.5 and 0.05 pCi/gm, respectively. Thirty rem was selected as the thyroid dose acceptance criteria for a steam line break with an assumed accident initiated iodine spike based on the guidance of the Standard Review Plan (NUREG-0800) Section 15.1.5, Appendix A. Only the release of iodine and the resulting 4-1
F o . l thyroid dose was considered in the leak rate determination. Whole-body doses due to noble f gas immersion have been determined, in other evaluations, to be less limiting than the , corresponding thyroid doses. .l i The salient assumptions for the limiting, accident initiated iodine spike follow. , e Initial primary coolant iodine activity - 1 pCi/gm DE I-131 j
~
u Initial secondary coolant iodine activity - 0.1 pCi/gm DE I-131 l l e Steam released to the environment (0 to 2 hours) ,
- from 2 SG's in the intact loops, 375,000 lb
- from the affected SG, approximately 99,300 lb (the entire initial SG water mass) .
e Iodine partition coefficients for primary-to-secondary leakage ;
- SG's in intact loops,1.0 (leakage is assumed to be above the mixture level) j
- SG in faulted loop,1.0 (SG is assumed to steam dry) ;
e Iodine partition coefficients for activity release due to steaming of SG water
- SG's in intact loops,0.1
- SG in faulted loop,1.0 (SG is assumed to steam dry) !
e Atmospheric dispersion factor (SB 0 to 2 hours),8.9E-4 sec/m' (Note: the value of 1 2.23E-4 sec/m' reported in WCAP-13579 is in error; 8.9E-4 sec/m' was used for both j evaluations) e Thyroid dose conversion factor per ICRP 30 (International Commission on ; Radiological Protection, " Limits for Intakes of Radionuclides by Workers", Publication 30, 1979). The thyroid dose conversion factors provided in ICRP 30 were issued as ! the first revision to the dose conversion factors that were originally provided in : ICRP 2 , " Report of ICRP Committee II on Permissible Dose for Internal Radiation", j 1959. (ICRP 2 is the source of the TID-14844 dose conversion factors.) Note that only the dose calculation utilizes ICRP-30. The initial primary coolant dose equivalent ! iodine activity is based on ICRP-2. + i The activity released to the environment due to a main steam line break can be separated into ! two distinct releases: the release of the iodine activity that has been established in the ; secondary coolant prior to the accident and the release of the primary coolant iodine activity ; that is transferred by tube leakage during the accident. Based on the assumptions stated l previously, the release of the activity initially contained in the secondary coolant (3 SGs) ! results in a site boundary thyroid dose of approximately 2.0 rem. This dose is independent of l the leak location (s). ! i The dose contribution from I gpm of primary-to-secondary leakage (3 SG's) is approximately l 4.09 rem. Thus, the total allowable leak rate is 6.8 gpm [(30 rem - 2.0 rem) / (4.09 rem /gpm)). 1 4-2 i i 6
f
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Each of the SG's in the intact loops is assumed to leak at 0.1 gpm (~130 gpd), which is the proposed Technical Specification LCO for implementation ofIPC. By subtracting the assumed leakage in the SGs of both intact loops from the total allowable leak rate, the allowable leak rate for the SG in the affected loop is 6.6 gpm [6.8 gpm - (2 x 0.1 gpm)). 1
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5.0 DATABASE SUPPORTING ALTERNATE REPAIR CRITERIA This section describes the database to be used for the ARC correlations of Section 6.0 and the SLB analysis of Section 8.0. The database recommended for the Beaver Valley 2 0 volt IPC is the EPRI ARC database of Reference 3. At this time, the NRC has not completed their review of the EPRI 7/8" tubing outlier evaluation of Reference 3. The differences in the databases currently approved by the NRC based on Spring 1994 Farley-1 and D. C. Cook-1 SERs and the EPRI ARC database are described in Section 5.2. As described in Sections 6 and 8, the EPRI database is more conservative for SLB leek rate analysis using draft NUREG-1477 methodology. Thus, the EPRI database can H. used for leak rate analyses based on draft NUREG-1477. The probability of burst analyses are provided for information only, since these analyses do not impact the repair limits or the number of tubes to be repaired. For this report, the EPRI recommended ARC database is the latest database and is applied for IPC tube burst probability analyses. The IPC requires a voltage limit, above which tubes require repair independent of confirmation of the bobbin flaw indication by RPC inspection. A repair limit of 3.6 volts (see Section 8.2), from the Farley-1 and Cook-1 SERs, is adopted for the Beaver Valley IPC. This 3.6 volt repair limit is lower than that of a full APC repair limit independent of the EPRI or NRC recommended database. Thus, based on supplemental analyses given in Sections 6.0 and 8.2,it is concluded that the EPRI ARC database can be used for Beaver Valley IPC applications. However, the EPRI SLB leak rate versus voltage correlation, as recommended for the Beaver Valley 2.0 volt IPC, has significant differences between the EPRI and current NRC-approved database. Thus, it is important for the NRC to complete its review of the EPRI database of Reference 3 for the Beaver Valley IPC. 5.1 EPRI ARC Database The database for 7/8 inch diameter tubing is described in EPRI Report NP-7480-L, Volume 1, Revision 1 (Reference 2). However, at the February 8,1994 NRC/ Industry meeting, the NRC presented resolution of industry comments on draft NUREG-1477. The NRC identified guidelines for application of leak rate versus voltage correlations and for removal of data outliers in the burst and leak rate correlations. The EPRI evaluation applying the NRC guidance on removal of outliers to update the database for the 7/8 inch tubing correlations has been submitted to the NRC by Reference 3 as a draft Appendix E revision to Reference 2. In Reference 2, data were removed from the EPRI database based on less explicit criterie. than that of Reference 3. The updated criteria lead to a change in one data point from Reference 2. Plant D 1 tube RllC60, TSP 1, which was previously deleted for atypical morphology, is added back into the database. No new data for 7/8 inch diameter tubing has been obtained since the preparation of Reference 2. The data of Reference 2 are updated for the present application based on the outlier evaluation of Reference 3. Table 5-1 summarizes the data having burst pressure and leak rate tests. Table 5-2 summarizes the data for use in the probability ofleak correlation. These tables are applied to develop correlations for ARC applications in Section 6.0. 5-1
At the time of this report, the NRC has not yet provided concurrence with the EPRI ARC database transmitted by Reference 3. 'Ihe latest NRC documented database acceptance is that provided in the Farley-1 and Cook 1 SERs. The differences between the current NRC-accepted database and the EPRI database described above are:
. NRC Additions to Burst Pitssure versus Voltage Correlation
. For the data of Table 5-1, the following data points would be included in the burst correlation per the guidance of the Parley-1 and D. C. Cook-1 SERs:
- Plant D-1: RllC60 - TSP 2, R18C16 - TSP 1, R18C21 - TSP 1 PlantF: R13C42 - TSPs 1 & 2, R16C29 - TSP 1, R16C42 - TSPs 1 & 2 These data points were exc'.ided from the EPRI database per Criterion 2a of l Reference 3. This criterion excludes data from the EPRI correlations based on track {
morphology atypical of the ARC database. In these cases, the lack of remaining ) uncorroded ligaments in the shallow indications resulted in high voltages for the given i degradation levels and associated burst pressures, which led to very high outlier behavior in the burst pressure versus voltage correlation. In principal, these 1 indications should also be included in the probability of leakag: (POL) correlation. ; However, since all of these indications are non-leakers, it is conservative to not include them as applied for the EPRI ARC database. The Beaver Valley IPC POL correlation does not include these indications. All burst correlations used in this report are based on the EPRI database. NRC Additions to SLB Leak Rate Database and Correlations For the data of Table 5-1, the current NRC database would include the following indications in the SLB leak rate analyses as applied to the draft NUREG-1477 methodology or the EPRI SLB leak rate versus voltage correlation: Model boiler specimen $42-4, with a bobbin voltage of 50.3 volts and a SLB leak rate of 0.861/hr. Plant J-l pulled tube R8C74 - TSP 1, with a bobbin voltage of 30.9 volts and a SLB leak rate of 0.131/hr. These data points were excluded from the EPRI database per Criterion 3 of Reference 3. The criterion excludes data from the EPRI correlations based on SLB leak rates less than 10% higher than normal operating conditions (Specimen 542-4) or less than 50 times the leak rate of specimens containing similar through wall degradation and voltage responses (R8C74). In these cases, it is expected that the cracks likely became plugged by deposits during leak testing and the resulting leak rates are much lower than expected as represented by the rest of the database. The EPRI database is applied for the SLB leak rate correlations applied in this report. 5-2
l 5.2 NDE Uncertainties For IPC applications, NDE uncertainties are required to support projections of EOC voltage 1 distributions, SLB leak rates and SLB tube burst probabilities as discussed in Section 8.0. l The database supporting NDE uncertainties is described in Reference 2, and NDE
- uncertainties for IPC/APC applications are given in the EPRI repair criteria report (Reference 1). From Reference 1, the NDE uncertainties are comprised of uncertainties due to the data acquisition technique, which is based on use of the probe wear standard, and due to analyst interpretation, which is sometimes called the analyst variability uncertainty.
The data acquisition (probe wear) uncertainty has a standard deviation of 7.0% about a mean of zero and has a cutoff at 15% with implementation of the probe wear standard requiring ! probe replacement at 15% differences between new and wom probes as described in Appendix A. The analyst interpretation (analyst variability) uncertainty has a standard deviation of 10.3% about a mean of zero. Typically, this uncertainty has a cutoff at 20% based on requiring ; resolution of analyst voltage calls differing by more than 20% as described in Appendix A. i However, as of the February 8,1994 meeting, the NRC has not accepted the 20% cutoff on , the analyst interpretation uncertainty. Pending a further resolution of this issue with the NRC, i it is planned that the analyst interpretation uncertainty would conservatively be applied without a cutoff. For EOC voltage projections, separate distributions will be applied for the data acquisition with a cutoff at 15% and the analyst interpretation with no cutoff. 5-3
Table 5-1 7/8-Inch Diameter Pulled and Model Boiler Tube Leak Rate and Burst Pressure Measurements Adjusted Correladon SLBLeak Bob b Con Burst Application") RPC Destrucdve Esasa Rate (nr)') specimen Pressure"3 Vohs Leak Burst No. or Mat length0) (pagy 2560 AP Rate Plant Row / Col TSP Depth (in,) - Volta"3 Depth (See notes at bottom of last page) tow n
( Table 5-1 7/8-Inch Diameter Pulled and Model Boller Tube Leak Rate and Burst Pressure Measurements l Bokble CoS SLB Leak Adjusted Correlation specimen RPC Destructhe Esam Rate (Wr)D) Burst A ppucation") Na,or Volts Pressure") Plant Row / Col TSP Mao lang#3 (p.g) 14ak Burst Volta") Depth Depth On.) 2560 AP Rate e
= ' (See notes at bottom of last page) -
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ll l l l l 1 Table 51 7/8-Inch Diameter Pulled and Model Boiler Tube Leak Rate and Burst Pressure Measurements Bobbin Cou SLB Leak Adjusted Corniation Specisnen RPC Destructive Enam Rate (1/hr)"3 Bunt A pplication"3 No. or Volts Preasur/*3 Plant Row / Col TSP Ma s. Length 83 (paf) leak Burst Vod:U, Depth Depth 1560 AP On.) Rate l (See notes at bottom of last page) ~ TAALR3 5 3
Table 5-1 l 7/8-Inch Diameter Pulled and Model Boiler Tube Leak Rate l and Burst Pressure Measurements Bobbla cog SLB Leak Adjusted Correlation Specisnen RPC Destmetite Esam Rate (Wr)') Burst Application") No.or Volts Pressure") Plant Row Col TSP Mas. 14 mph8) (pg) laak Burst
' VoltsM Depth Depth (In.) 2560 AP Rate
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Table 5-2: Database for Probability of Leak foi. 7/8" Diameter Tubes Bobbm * ' Pmbebility d Plant or Model Arnpimk Wility d gg , u l Soiler Sarnpk leak (Volt 4 .e Number Number (Volts) m m d e W W se m 4 m RFK S/4S4. 4.00 PM psSUMOAT ASI Prob Leak
l l
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6.0 TUDE BURST AND SLB LEAK RATE CORRELATIONS 6.1 EPRI ARC Correlations As part of the development of alternate repair criteria (ARC), correlations have been developed for tubes containing ODSCC indications at TSP locations between the bobbin amplitude, expressed in volts, of those indications and the free span burst pressure, the probability of leak, and the free-span leak rate for indications that leak, References (1) and (2). 'Ihe database used for the development of the correlations is presented and discussed in Reference (2). Guidelines for the identification and exclusion of inappropriate data, termed outilers, are provided in Reference (3). The resulting EPRI database is given in Tables 5-1 and 5-2. In addition to the aforementioned, an empirical correlation curve for the burst pressure as a function of crack length has been developed for tubes with free-span, through-wall, axial cracks. In 1993, the NRC issued draft NUREG-1477, Reference (6), for public comment. The draft NUREG delineated a set of guidelines for criteria to be met for the applicatiori of Interim Plugging Criteria (IPC) for ODSCC indications. The criteria guidelines permitted the use of, with adequate justification, a burst pressure to bobbin amplitude correlation and a probability ofleak to bobbin amplitude correlation. The criteria guidelines did not permit the use of a leak rate to bobbin amplitude correlation for the estimation of end of cycle (EOC) total leak rates. In essence, References (1) and (2) provided comments on the Reference (6) guidelines. Reference (7) provided an NRC response and position relative to resolving the differences between References (1) & (2) and Reference (6), along with responses to other public comments. Of signi6cance to this report, is that Refe'rence (7) indicated that a correlation between leak rate and bobbin amplitude could be employed if the correlation could be statistically justified at a 95% confidence level, and provided direction for the development of guidelines, e g., Reference (3), that could then be employed for the identification and exclusion of outlying experimental data. Subsequent discussions with NRC personnel have revealed potential issues associated with the manner in which the leak rate to bobbin amplitude correlation is used, thus, the potential leak rate during a postulated steam line break (SLB) is estimated in Section 8, with and without the use of the correlation. The purpose of this section is to provide information and justification for all of the correlations develnped in support of the application of an IPC for the Beaver Valley Unit I nuclear power plant. Information is first presented relative to the correlation of burst pressure to bobbin amplitude and to through wall crack length, followed by a discussion of the correlation between the probability of leak and the bobbin amplitude, and lastly a discussion of the correlation ofleak rate to bobbin amplitude. The use of each of the correlations is also documented. m.w6 wn 6-I wy n. im l l 1
p A ' l 6.2 Burst Pressure vs. Bobbin Voltage Correlation The bobbin coil voltage amplitude and burst pressure data presented in the EPRI database report for 7/8" tubes, Reference (3), and Table 5-1, were used to estimate the degree of correla-tion between the burst pressure and bobbin voltage amplitude. 'Ihe details of performing the correlation analysis, and subsequent regression analysis to estimate the parameters of a log-
.. linear relationship between the burst pressure and the bobbin amplitude, are provided in the EPRI database report. The evaluations examined the scale factors for the coordinate system to I be employed, the detection and tre ement of outliers, the order of the regression equation, the !
potential for measurement errors in the variables, and the evaluation of the residuals following the development of a relation by least sqaares regression analysis. The results of the analyses l indicated that an optimum linear, first order rel. tion could be obtained from the regression of i the burst pressure on the common logarithm (base 10) of the bobbin amplitude voltage. A linear, first order equation relating the burst pressure to the logarithm of the bobbin ; amplitude was developed.. Examination of the residuals from the regression analysis indicated - l that they were normally distributed, thus verifying the assumption of normality inherent in the use of least squares regression. The regression curve (line)is given by
- P,, = a, + a, log (V,)
(6.1)
= 8.239 -2.529 log (V,),
where the burst pressure is measured in ksi and the bobbin amplitude is in voltr. The index of determination for the regression was 82.7%, thus the correlation coefficient is 0.91, which is significant at a >99.999% level. This means that the p-value for the slope of the line is [
< 0.001%. "Ihe estimated standard deviation of the residuals, i.e., the error of the estimate, s,, !
of the burst pressure was 0.89 ksi. A summary of the results from the regression analysis is [ provided in Table 6-1. r The database and the regression curve are illustrated on Figure 6-1. Using the regression relationship, a lower 95% prediction bound for the bu'rst pressure as a function of bobbin amplitude was developed. These values were further reduced to account for the lower . ; 95%/95% tolerance bound for the Westinghouse database of tubing material properties at 650*F. Both of these are also depicted on Figure 6-1. Using this reduced lower prediction bound, the bobbin amplitude corresponding to afree-span burst pressure of 3657 psi was found f DLW6 WP3 6*2 wy it im i
to be 8.82 V. The value of 3657 psi results from considering a SLB differential pressure of 2560 psi divided by 0.7 in accord with the guidelines of RG 1.121, Reference (8), i 6.3 Burst Pressure vs. Through Wall Crack Length Correlation For a tube with a mean radius of r, and a thickness t, the normalized, i.e., non-dimensional-ized, burst pressure as a function of the actual burst pressure, P,, is given by P8 r" P"' = . (6.2) (Sr+ S u) # Thus, Pw is the ratio of the maximum Tresca stress intensity, taking the average compressive stress in the tube to be P,/2, to twice the flow strength of the material. The normalizing parameter for crack length, a, is given by a A" . (6.3)
} r, t a form which arises in theoretical considerations of th'e burst problem. The burst pressure as a function of axial crack length for a specific tube size is then easily obtained from the non-dimensionalized relationship.
Examination of the normalized burst pressure database indicated that a variety of functional forms would result in similar fit characteristics. An exponential function, i.e., 8 1 Pu, = b, + b, e 1, ('#} was finally selected based on the combination of maximizing the goodness of fit, and minimizing the number of coefficients in the function. Equation (6.4) was also found to be advantageous in that it can easily be inverted to yield A as a function of Pu,. For the data analyzed, the coefficients of equation (6.4) were found to be l
~
1 8'" (6.5) P,, = 0.0615 + 0.534 e l The index of determination for the fit was 98.3%, with a standard error of the estimate of O.015. The F distribution statistic for the regression, the ratio of the mean square due to the regression to the mean square due to the residuals, was 4625. Thus, the fit of the equation to the data is excellent. Note that this does not mean that equation (6.4)is the true form of a DLW6 WP5 6-3 wy is. m
functional relationship between the two variables, only that it provides an' excellent description of the relationship. Equation (6.4) was then rearranged to yield the inverse relation ,
)
P, - 0.0615 (6.6) A = - 3.6111n ,
, 0.534 ,
for the normalized crack length as a function of normalized burst pressure. -{
' In order to present the results in a form directly applicable to the Beaver Valley Unit l tubes, the normalized relationships were adjusted to correspond to 0.875" diameter by 0.050" thick l tubes having a flow stress of 68.8 ksi, the average of the Westinghouse database. The adjusted l database, the regression curve, and the regression curve adjusted for lower 95%/95% tolerance !
limit material properties are shown on Figure 6 2. For a tube with lower tolerance limit (LTL) ; material properties the critical free-span, axial crack length corresponding to a burst pressure of. 2560 psi would be 0.84". The length corresponding to a burst pressure of 3657 psi would be j expected to be 0.54". ! Using the regression results, the probability of burst during SLB was estimated as a function of crack length. The mean estimate of the burst pressure is given by the regression equation as [ t P, = Pu't (Sr + Su )- t (6.7)
,= >
i An unbiased estimate of the variance of P, which accounts for the variation in Pwabout the regression curve and the variation in Sr+8u can be calculated as ! 2t (6.8) V ( P ,) = _ p,2 y(g,) 3; y(p u,) _ y( p u,) y(g;)
. R. ,
where V is used to represent an unbiased estimate of the variance of the respective term in parentheses, and jS , the flow stress for Alloy 600 material, is one-half of the sum of the yield - and ultimate strengths. Taking the standard deviation of the burst pressure as the square root of the estimated variance allows for the estimation of the probability of burst using a Student's , t-distribution. Specifically, the difference between the estimated burst pressure for a given , crack length, a, and the SLB pressure is divided by the estimated standard deviation of the burst pressure to obtain a t. deviate. The probability of occurrence of the value of t is then an estimate of the probability of burst for that crack length during a SLB. The number of degrees DLW6 WPS 6-4 My M. N N r n . _ , _ _ _ _ _ _ _ _ _ _ _ _ ~ _______m._-- _ _ _ . _ _ _ . _ _ _ _ _ _ . _ _ _ _ . _ _ _ _ . _ _ _ . _ - - r--r-.m--- - - - - - _ _
i
- i of freedom used in estimating the probability of occurrence of a t-deviate greater than t is conservatively taken as the lesser of the number of degrees of freedom of Pw orfS An j alternate estimate of the probability of burst can be obtained by simulating Pa and Sf independently. In this case, a large number of values of Pw and Sj are independently calculated using randomly generated independent t-variates and the respective estimated standard deviations of Fw bout a the regression curve and Sfabout the mean of the database. i These are then combined using equation (6.7) to obtain a burst pressure for a single simulation. '
l The number of occurrences of the calculated burst pressure being less than the SLB pressure is then an estimate of the probability of burst. Based on the specific simulation results an upper bound for the estimate of the probability of burst may then be made using non-parametric I methods. The results of the calculational and the Monte Carlo simulation determinations are depicted on Figure 6-3. Also shown are the 99% upper confidence bounds for the Monte C:.do estimated values. The calculational procedure is seen to lead to a conservative estimate of the i probability of burst for a given crack length. An examination of the distribution of the of burst pressures from the Monte Carlo simulations reveals that it is skewed right. Thus the tail of the distribution is shorter for the lower burst pressures, hence the lower probabilities of burst. 6.4 NRC Draft NUREG-1477 SLB Leak Rate POD and Uncertainty Methodology The NRC methodology of draft NUREG-1477 obtains the number ofindications that are to be considered as being retumed to service, N, as: N -Ng + Na- N, = N, + I ~ # N g- N, = - N,, % POD POD where, Ng = the number of detected bobbin indications, N, = the number of repaired indications, Na = the number of indications not detected by the bobbin inspection, POD = the probability of detection (0.6 for NRC methodology). The above adjustments for POD have been incorporated in the BOC and EOC voltage distributions so that no further adjustments are required for the leakage calculation. Section 3.3 of draft NUREG-1477 states that the total leak rate, LR, should be determined as. ; l LR = p P + 2 0P+pPp2 g(y,p,2) 2 2 (6.10)
$ i DLW6 WP5 6-$ My1$,HH l
where, p = the mean of the leak rate data independent of voltage, o = the standard deviation of the leak rate data independent of voltage,- P, = the probability that a tube leaks for the' f voltage bin, N, = number of indications (after POD adjustment) in the P voltage bin, P = E,(N,P,) = expected number of indications that leak summed over all voltage bins, 2 = standard normal distribution deviate (establishes level of confidence on leakage). l l For the total leakage, the first term of the above equation represents a mean expected leak rate while the square root term is an effective standard deviation for the total leakage based on the variance of the product of the probability ofleak and the predicted leak rate. Draft NUREG-1477 recommends that Z be taken as 2, corresponding to an upper bound confidence of 98%. I l 6.5 Probability of Leakage Correlations
.i Historically, the probability ofleakage has been evaluated by segregating the model boiler and !
field data into two categories, i.e., specimens that would not leak during a SLB and those that would leak during a SLB. These data were analyzed to fit a sigmoid type equation to establish an algebraic relationship between the bobbin amplitude and the probability ofleak. The i specific algebraic form used to date has been the logistic function with the common logarithm ! of the bobbin amplitude employed as the regressor variable, i.e., letting P be the probability of leak, and considering a logarithmic scale for volts, V, the logistic expression is: , I P(leak l V) = (6.11) j ,,-k m u mi. ! This is then rearranged as: t In = a, + a, ' log ( V) , (6.12)
,1 - P ,
to permit an iterative, linear, least squares regression to be performed to find the maximum likelihood estimators of the coefficients, ao and a,. Reviews of those evaluations, e.g., NUREG-1477, have resulted in the NRC requesting that alternate sigmoid function forms be investigated, and that the evaluations also consider the potential dependence to be on the bobbin amplitude instead of the logarithm of the bobbin amplitude. NUREG-1477 specifically mentions that the cumulative normal, or Gaussian, f otw6 wes 6-6 wy is. im
9 ( distribution function and the Cauchy distribution function be investigated. Discussions with NRC personnel led to the stipulation that these functions be analyzed and used in predicting the end-of-cycle leak rate for the Farley-1 and D. C. Cook-1 IPC evaluations. I . The use of the logistic function for the analysis of dichotomous data is standard in many fields. As noted, the function is sigmoidal in shape, and is similar to the cumulative normal function, and likewise similar to using a probit model (which is a normal function with the deviate axis shifted to avoid dealing with negative values). In principle, any distribution function that has a cumulative area of unity could be fit as the distribution function, a limitless number of possi-bilities. Trying to identify a latent, or physically based, distribution for the probability ofleak would be considered to be unrealistic and unnecessary. For most purposes the logistic and normal functions will agree closely over the mid range of the data being fined. The tails of the distributions do not agree as well, with the normal function approaching the limiting probabilities of zero and one more rapidly than the logistic function. Thus, relative to the use of the normal distribution, the use of the logistic function is conservative. Given its wide ; I acceptance in multiple fields it was judged that the logistic function would be suitable for use l in determining a probability of leak as a function of voltage. In addition, consideration was given as to whether the bobbin amplitude or the logarithm of the bobbin amplitude should be used. Since the logistic, normal and Cauchy distribution functions aie unbounded, the use of volts would result in a finite probability of leak from non-degraded tubes, and would be zero only for Va-=. By contrast, the use of the logarithm of the voltage results in a probability ofleak for non-degraded tubes of zero. Clearly, the second situation is more realistic than the first, especially in light of the fact that a voltage threshold is a likely possibility. To comply with the NRC request, however, each distribution function was fitted to the data using the logarithm of the bobbin amplitude and the bobbin amplitude as the regressor. j The three functions to be evaluated fall into a category of models referred to as Generalir,ed l Linear Models (GLM's). This simply means that the models can be transformed into a linear form, e.g., equation (612). The left side of equation (6.12) is referred to as the link function for the logistic model. For the normal or cumulative Gaussian distribution function the model to be fitted is: W sm 7,. I (6.13) F(leak) = I c dz, (ii :- DLW6 WPS 6-7 M H. Im
and for the Cauchy distribution function the model to'be fitted is: (6.14) P(leak) = 1 + 1 tan-'[a, + a, log (V)]. 2 n The link function for the Gaussian function is: (6.15) y = 4 -'(P) = a, + a, log ( V), while for the Cauchy function the link function is: r r 3 s- (6.16) q = tan n P = a, + ai log (V) . g 2,, To fit the equation forms to the bobbin amplitude rather than log of tite amplitude, Vis substituted for log (V). Each equation was fitted to the data using an iterative least squares technique, which results in the maximum likelihood estimates of the parameters. The resalts of all of the regression analyses using the EPRI database (Table 5 2) are summa-rized in Table 6-2. The coefficients of the equations are provided along with the elements the variance-covariance matrix for the coefficients. In addition, the deviance for each soluti is also given. One accepted measure of the goodness of the solution or fit for GLM's is deviance, D, given by,
- 1-P (6.17)
P' + (1 - P,) In # D =2 { P, in 1 - P(V,)
.i ,
P(V,) where P,is the probability associated with data pair i and P(V)is the calculated proba from V, The deviance is used similar to the residual sum of squares in linear regression analysis and is equal to the error, or residual, sum of squares (SSE) for linear regressio the probability ofleak evaluation P,is either zero or one, so equation (6.17) may be wr n , (6.18) D = - 2 { } P,ln[P(v,)) + (1 - P,)ln[1 - P(v,)]f . del Since the deviance is similar to the SSE, lower values indicate a better fit, i.e., the lower the residual sum of squares the more of the variation of the data is considered to be explained I wy is. im 6-8 etws wes
the regression equation. The smallest deviance is obtained from the log normal fit with the log logistic fit providing the next smallest deviance. The difference between the two is not judged to be significant. The next best fit was obtained with the normal' fit. The deviance using either Cauchy form is about 15% to 20% percent higher than for the other functions. Inclusion of the outliers in the log logistic evaluation increased the deviance from 25.1 to 25.2. The results of fitting each of the equations are depicted on Figure 6-4 and Figure 6-5. A comparison of the results shown on Figure 6-4 with those shown on Figure 6-5 indicates that the use of the logarithm of the volts results in a spreading of the functions with the probability ofleak at, say,3 volts being higher for the logarithmic forms. In the very low voltage range, less than 1 volt, the probability of leak is lower for the logarithmic forms. This is due to the fact that the tails must extend to -=. In general, the Cauchy cumulative distribution function : has longer tails than either the logistic or normal functions. It also rises much more sharply in l the middle of the data range. The regression results on Figure 6-5 illustrate the non realistic nature of the Cauchy fit for the non-logarithmic form. Examination of the figures indicates that the Cauchy distribution is less representative of the data in the regions where the no leak ; and leak test data overlap. Figure 6-6 is provided to compare the resula of the log logistic correlation with and without the inclusion of outliers in the analysis. A dsussion of these ! results is provided later in this section. l A listing of probability ofleak results for selected volts is provided in Table 6-3. For a bobbin amplitude of 1 volt, predictions based on the 1.og normal function are at least an order of magnitude less than predictions based on the log-logistic function. For very high voltages the Cauchy distributiw forms rise to a probability ofleak of one slower than the other distribution functions. Taken in conjunction with the leak rate versus voltage correlation, the choice of a probability of leak function is relatively moot. The final total leak rate values tend to differ by only a few percent across the spectrum of POL functions. 6.6 SLB Leak Rate Versus Voltage Correlation for 7/8" Tubes The bobbin coil and leakage data previously reported (EPRI database of Table 5-1) were used to estimate a correlation function between the SLB leak rate and the bobbin amplitude voltage. Since the bobbin amplitude and the leak rate would be expected to be functions of the crack morphology, it is to be expected that a correlation bet' ween these variables would exist. Previous plots of the data on linear and logarithmic scales indicated that a linear relationship between the logarithm of the leak rate and the logarithm of the bobbin amplitude would be an otw.wes 6-9 wr u. m
n j i appropriate choice for establishing a correlating function via least squares regression analysis. Thus, the functional form of the correlation is log (Q) = b, + b, log (V), (6.19) where Q is the leak rate, Vis the bobbin voltage, and be and b, are coefficients that are estimated from the data. The final selection of the form of the variable scales, i.e., log-log, was based on performing least squares regression analysis on each possible combination and examining the index of determination, r 2, for each case. Given the results, it was not obvious whether the appropriate choice of axes scales should be linear linear or log-log. The index of determination for the regression of Q on V was about 10% less than that for log (Q) on log (F), thus indicating some question relative to the choice of scales. However, similar analysis of data for 3/4" diameter tubes yielded an index of determination of 24% for Q on V and 58% for log (Q) on log (V), clearly indicating the appropriate choice of scales to be log-log. A summary of the results of the regression analysis is provided in Table 6-4. The number of data pairs used for the above evaluations was 24 and the number of degrees of freedom (dof)
- 22. The obtained value of r 2of 38.6% is significant at a level of 99.88% based on an F distribution test of the ratio of the mean square of the regression to the mean square of the error. This can also be interpreted as the probability that the log of the leak rate is correlated tc the log of the bobbin amplitude. An alternate interpretation is that if the variables are really uncorrelated and the testing was repeated many times, an index of determination equal to or greater than that obtained from the analyzed data would be expected to occur rardomly in only 0.12% of those tests. Similar analysis of the data for 3/4" diameter tubes resul' . in a significance level of >99.999% with a random probability of occurrence of the level of the observed correlation of only 1.810 4 If the variables are truly uncorrelated, then the joint probability of occurrence.of the observeo correlations would be ~2.210", with an attendant probability that the variables are correlated of ~1 - 2.210'" The conclusion to be drawn from these results is that it is very likely that the variables are correlated.
At the February 8,1994, meeting between the NRC, EPRI, and NUMARC, information was presented by the NRC that the "use of linear regression is acceptable if shown to be valid at a 5% level with [a] p-value test." It was also noted that the " constant leak rate model in [the] draft NUREG [-1477] should continue to be used until [the] linear model is shown to be valid." The p-value is the conditional probability of observing a computed statistic, e.g., the F distribution value reported above, as large or larger than the observed value, under the condition that there is no relationship. In this case, a small p-value is evidence against the null hypothesis that there is no correlation between log (Q) and log (F). The p-values for the estimated parameters of Equation (6.19) are also given in Table 6-4. For the regression equation the conditional probability that the slope is zero is 0.12%. The conditional probability DLW6 WP5 6 - 10 wy is. im
that the intercept is zero is 1.93%. The validity of the regression is judged by the p-value l associated with the slope. Since this is significantly less than the 5% value as stipulated l above, the regression is concluded to be valid, and the use of linear regression is acceptable. On the basis that the NRC bas not completed its review of the use of the conditional leak rate ' model in conjunction with the POL model, the NRC has stipulated that a leak rate calculation be performed per the methodology described in NUREG-1477 (which does not admit the use of a regression equation). Thus, EOC leak rate values under postulated SLB conditions are reported for both calculational methods, although the EPRI leak rate correlation is recommended for Beaver Valley-l. In order to determine if the parameters of the relationships were being biased by the presence of unduly influential data points, a least median of squares regression analysis was performed on the data set for the log (Q) versus log (V) regression. Four points were identified as potential outliers for a AP of 2.560 ksi. An examination of the testing programs' information associated with these data revealed no basis for rejecting the data, thus they were retained for the analysis. The expected, or arithmetic average (AA), leak rate, Q, corresponding to a voltage level, V, was also determined from the above expressions. Since the regression was performed as log (Q) on log (V) th'. regression line represents the mean of log (Q) as a function of bobbin amplitude. This is not the mean of Q as a function of V. The residuals oflog(Q) are expected to be normally distributed about the regression line. Thus, the median and mode of the log (Q) residuals are also estimated by the regression line. However, Q is then expected to be distributed about the regression line as a log-normal distribution. The regression line still estimates the median of Q, but the mode and mean are displaced. ' Die corresponding adjust-ment to the normal distribution to obtain the AA of Q for a log-normal distribution is a %* (6.20)
= E{ Q l V} = 10 ,Pam + *2 ,
2 for a given V, where 0 is the estimated variance of log (Q) about the regression line. The variance of the expected leak rate about the mean expected leak rate is then obtained from W (6.21) Var (Q) = Q *(e 'W - 1 ). To complete the analysis for the leak rate, the expected leak rate as a function of log (V) was determined by multiplying the arithmetic average leak rate by the probability of leak as a om wn 6 - 11 % is. im
l function of log (V). The results of this calculation are also depicted on Figure 6-7 for a steam line break differential pressure of 2560 psi. Analysis of Regression Residuals As previously noted, the correlation coefficients obtained from the analyses indicate that th . log-log regressions at the various SLB APs are significant at a level greater than 99.8%. Additional verification of the appropriateness of the regression was obtained by analyzing the regression residuals,i.e., the actual variable value minus the predicted variable value fro regression equation. A plot of the log (Q) residuals as a function of the predicted log (Q) wa found to be nondescript, indicating no apparent correlation between the residuals and the predicted values. A cumulative probability plot of the residuals on normal probability paper approximated a straight line, thus verifying the assumption inherent in the regression ana that the residuals are normally distributed. Given the results of the residuals scatter plots and the normal probability plots, it is considered that the regression curve and statistics can be use for the prediction of leak rate as a function of bobbin amplitude, and for the establishment of statistical inference bounds. 6.7 SLB Leak Rate Analysis Methodology A complete discussion of the leak rate analysis methodology applied for the evahmion of the Beaver Valley SG tubes is contained in Reference (9). The leak rate versus voltage correlation can be simulated in conjunction with the EOC voltage distributions obtained by Monte Carlo methods, or by applying the POL correlation and leak rate correlation to the EOC voltage distribution obtained by Monte Carlo methods as described in draft NUREG-1477, Reference (6). This second approach is a hybrid that joins the Monte Carlo results with deterministic calculations. Parallel analyses have verified that the full Monte Carlo leak rates and the application of the correlations to the EOC voltage distribution yield essentially the same results for a 95% confidence limit on the total leak rate. Thus, it is adequate to apply the correlations to the EOC voltage distributions for estimating total leak rate up to a 95%
~
confidence level. The determination of the end or' cycle leak rate estimate proceeds as follows. The beginning of cycle voltages are estimated using the methodology provided in draft NUREG-1477. The distribution of indications is binned in 0.lv ircrements. The number ofindications is divided by 0.6 to account for POD. The resulting number of indications in each bin is reduced by the number of indications plugged in each bin. The final result is the beginning of cycle distribution used for the Monte Carlo simulations. The NDE uncertainty and growth rat distributions are then independently sampled to estimate an end of cycle distribution, also reported in bins of 0.lV increment. I wy is, im 6 - 12 r tw6wn
l l Using the hybrid methodology, the leak rate versus bobbin amplitude coirelation is used to I l estimate an expected, or average, leak rate for indications in each voltage bin. The probability ofleakage correlation is then used to estimate the mean probability of leak for the indications in each bin. The relationships derived in Appendix C of draft NUREG-1477 for the variance l of the product of the probability ofleak with the leak rate and for the total leak rate are then used to estimate the expected total leakage and variance for the sum of the indications in each bin as a function of the correlation means and estimated variances for the leak rate and probability of leak. The expected total leakage for the entire distribution is then obtained as the sum of the expected leak rates for each bin. The variance of the total leak rate for the distribution is cbtained as the sum of the variances for each bin. The standard deviation of the total leak rate is then taken as the square root of the variance of the total leak rate. The upper bound 95% con &dence limit on the total leak rate is then obtained as the expected total leak rate plus 1.645 times the standard deviation of the total leak rate. As previously noted, the results obtained with this approach have been compared to results obtained from Monte Carlo simulations without significant differences being observed. The estimated, total end of cycle leak rate can also be calculated using Monte Carlo tech-niques, e.g., the method documented in the EPRI ODSCC report, Reference (1). In the Monte Carlo analysis the variation in the parameters, i.e., coefficients, and the variation of the dependent variable about the regression line is simulated. A 95% confidence bound on the total leak rate of Beaver Valley I was calculated using a Monte Carlo simulation to verify the results from the deterministic analysis, as described in Section 8. A comparison of selected inputs to the various analyses as a function of the database employed is provided in Table 6-5. For the leak rate analysis methodology described in NUREG-1477, the use of the EPRI database is conservative in that the mean arithmetic average, or expected, leak rate from the leak rate data is greater than that obtained from the NRC recommended database (discussed in Section 5.2 of this report). In addition, the standard deviation of the data is greater for the EPRI database. The differences are minor and would not be expected to significantly affect the outcome of the projection of the EOC total leak rate during a postulated SLB. Figure 6-6 illustrates a comparison of the log-logistic prediction curves for the probabili-ty of leak with (NRC recommended database) and without (EPRI recommended database) inclusion of outliers in the regression analysis. It is seen that the inclusion of the outlying data points has a negligible effect on the POL correlation results. otn wrs 6 - 13 w y is.i m
I i 9 Table 6-1: Regression Analysis Results - Burst Pressure vs. log (Bobbin Amplitude) 7/8" x 0.050" Alloy 600 NiA SG Tubes Parameter Value Value Parameter b; -2.529 8.239 b, SE b, 0.140 0.122 SE be r 2 0,827 0.891 SE P, F 324.2 68 DoF
~
S S,, 257.41 53.99 S S,,, Pr(F) 1.4E-27 40.242 SSu,g pi-v2ue 1.4E-27 4.1E-64 po-value o DLW6 WP5 6 - 14 Ny 15. Im _- - - _ - __________________________j
I Table 6 2: Results of Regression Fits of Logarithmic Forms of the Probability of Leak Distribution Functions to 7/8" OD Tube Data. Log-logistic Log-normal Log-Cauchy Parameters Parameters Parameters ao 6.8974 -3.7394 -15.0653 a, 8.3507 4.5779 17.7301 V,, 3.4999 0.7999 67.1114 Vn -3.8459 -0.8801 -76.9510 Vu 4.5822 1.0749 88.9730 Deviance 25.09 24.87 28.68 Results of Regression Fits of Non-Logarithmic Forms of the Probability of Leak Distribution Functions to 7/8" OD Tube Data. . Logistic Normal Cauchy Parameters Parameters Parameters a, -4.9991 -2.7359 -10.0508 a, 0.6565 0.3582 1.3877 V,, 1.2530 0.2608 25.9471 l Vn -0.1597 -0.0337 -3.4945 I Vu 0.0261 0.0062 0.4825 Deviance 26.06 25.40 30.50 I l DLw6 WP5 6 - 15 ser u. im
I Table 6-3: Sample Results for Probability of Leak for 7/8" SG Tubes Normal Cauchy Volts Log-Logistic Log-Normal Log-Cauchy Logistic Function Function Function Function Function Function 9.7E-03 7.lE-03 3.5E-03 3.2E-02 0.1 2.4E-07 1.0E-16
~~
1.6E-02 9.3E-03 5.3E-03 3.4E-02 0.5 8.2E-05 1.6E-07 ~ 8.7E-03 3.7E 02
~l.0 1.0E-03 9.2E-05 23E-02 1.3E-02 1.4E-02 4.0E-02 4.4E-03 1.7E-03 2.7E-02 1.8E-02 1.5 ~~~
~
~~
3.3E-02 2.4E-02 2.2E-02 4.3E-02
~~~5.~0 1.2E-02 9.lE-03 4.8E-02 4.6E-02 4.8E-02 5.4E-02 3.0 5.2E-02 6.0E-02 7.1E-02 8.5E-02 9.6E-02 7.0E-02 4.0 1.3E-01 1.6E-01 1.lE-01 1.5E-01 1.7E-01 9.9E-02 5.0 2.6E-01 2.9E-01 4.7E 4.0E-01 4.1E-01 4.0E-01 7.0 5.4E-01 5.5E-01 8.9E-01 8.3E-01 8.0E-01 9.2E-01 10.0 8.lE-01 8.0E-01
~~
9.2E-01 9.5E-01 9.4E-01 9.5E-01 12.0 8.9E-01 8.9E-01 9.5E-01 9.9E-01 1.0EMO 9.7E-01 15 0 9.5E-Ol 9.5E-01 9.6E-01 1.0E-H)0 1.0E+00 9.8E-01 20.0 9.8E-01 9.9E-01
~~
9.7E-01 1.0E+00 1.0E@0 9.9E-01 30.0 1.0E%0 1.0E+00 wy is, im I ot.w s wrs 6 - 16
- l. .
~
\
I i l Table 6-4: Regression Analysis Results for Fitting log (Leak Rate) vs log (Volts) for 7/8" Tubes Parameter Value Value Parameter b; 1.892 -1.518 he SE b, 0.508 0.601 SE bo ) r 2 38.6% 0.639 SE log (Q) F 13.85 22 DoF SS, 5.654 8.980 S S,,, Pr(F) 0.12 % 1.580 SS yn pi-value 0.12 % 1.93 % po-value ! I l 1 l 1 1
- l 1
otws wes 6 - 17 say is. im
1
)
Table 6-5: Differences in Correlations Obtained Using the NRC Recommended and the EPRI Recommended Databases Item NRC Recommended EPRI Recommended Databasem Database Draft NUREG-1477 Mean leak rate, p (lph) ~ 13.7 14.9 Standard Deviation, o (lph) 21.1 21.7 pol Correlation using Log-logistic Function ao(logitintercept parameter) -6.9940 -6.8974 a, (logit slope parameter) 8.4538 8.3507 Deviance 25.17 25.09 Leak Rate Correlation using Linear log (Q) on log (V) Regression a o(intercept parameter) N/A -1.5190 a, (slope parameter) N/A 1.8920 Index of Determination, r# N/A 38.6% Standard Error, o N/A 0.6390 Burst Pressure Correlation using Linear P, on log (V) Regression a o(intercept parameter) 8.567.9 8.2390
~
a, (slope parameter) -2.6689 -2.5291 Index of Determination, r2 73.5 % 82.7 % Standard Error, o 1.1821 0.8910 Notes: (1) Differs from the recommended database as described in Section 8.1. etwms 6-18 34 is, im
Figure 6-1: Burst Pressure vs Volts for 7/8" OD Alloy 600 SG Tubes EPRI Recommended Database, Reference or = 75.0 ksi @ 650 F y l 8 [76PV.OUT XLS] EPRI Data
Figure 6-2: Burst Pressure vs. Crack length 0.875" x 0.050", Alloy 600 MA Steam Generator Tubes @ 650 F, Average Flow Stress _ l l 1
i J 1 l Figure 6-3: Probability of Burst vs.Through-Wall Crack Length : ! 7/8" x 0.050" Alley 600 MA SG Tubes i i m i
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Figure 6-5: Probability of Leak for 7/8" SG Tubes Comparison of Non-Logarithmic Forms of the Logistic, Normal, & Cauchy Functions
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l 1 Figure 6-6: ProbabHity ofI2sk for 7/8" SG Tubes Comparision of Log-Logistic Function Solutions with & without Outliers 1.0 i i j j i i 1 i 0.9-- 3 ; w/o Outliers ; i* l
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Figure 6-7: SLB (2560 psi) IAak Rate vs. Bobbin Amplitude 7/8" x 0.050" Alloy 600 SG Tubes, Model Boiler & Field Data ,,, l RFK SNDs. 737 PM l78tKRATE XLS) O vs V
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7.0 BEAVER VA , LEY UNIT I SG INSPECTION RESULTS 7.1 Inspection Results The 1993 End-of-Cycle-9 (EOC-9) refueling outage included 100% full length bobbin probe inspection of all three steam generators. The indications reported at the TSPs have been assessed against prior inspection conditions at the corresponding locations to develop voltage growth rates for the operating intervals described below. _ Previous inspections of the Beaver Valley Unit 1 SG tubes were conducted in 1991,1989, and in 1987; 100% full length EC (bobbin) testing was performed in each of these years. Re-analysis of the original data was performed to the criteria of Appendix A for each of the inspections, including the 1993 inspection. Thus, growth populations appropriate to each operating interval were tracked to determine the progression of TSP ODSCC during the last three cycles, Cycles 7,8, and 9. A summary of the growth rates determined is presented for all three cycles in Table 7-1 on a per cycle basis; shown are the number of growth values obtained, the average beginning of cycle (BOC) amplitude along with its standard deviation, the m. mage growth in volts and its standard deviation, and the growth expressed as a percent of the BOC average voltage. The data is further sub-divided into populations less than 0.75 volts and those equal to or greater than 0.75 volts. This was done to demonstrate the consistency in behavior with the data from other plants which have applied the interim plugging criteria; in those cases, as well as in the Beaver Valley Unit I case, the lower voltage indications have consistently exhibited relatively higher growth rates than those determined for'the indications with amplitudes exceeding 0.75 volts. The distribution of the TSP ODSCC indications among the three SG's for the 1993 (EOC-9) inspection is presented in Table 7-2, which tabulates the number of indications for each TSP affected. For the 51 Series SG's in Beaver Valley Unit 1, the TSP IH through 7H levels represent typical support plates with nominal size tube holes and the normal circulation hole pattern; there is no flow distribution baffle in these SG's. The expectation, therefore, is that when TSP ODSCC occurs, it will exhibit diminishing extent as its distance or elevation from , the hot leg tubesheet increases. This is what has been observed, as can be seen from examination of Table 7-2 and from review of Figure 7-1, which portrays this information in histogram form. Although some probability of encountering ODSCC indications in the upper hot leg TSPs and cold leg supports does exist, it is common experience that almost all of the indications are observed at the first four hot leg TSPs. His is consistent with the natural I temperature gradient which results as the inlet temperature decreases due to heat exchange as the primary coolant courses through the tubes. 7.1.1 1993 Inspection During the Cycle 9 refueling outage, after 1.35 EFPY of operation, all tubes in service were tested full length with bobbin probes. Each distorted support plate indication (DSI) was subjected to rotating pancake coil (RPC) confirmation to assess the consistency of the underlying tube condition with prior cases of TSP ODSCC, and to determine the severity of the indication with respect to tube repair criteria. Tubes which exhibited RPC-confirmed TSP l 7-1
~
ODSCC indications were plugged. In all,428 tubes were plugged for this cause, distributed 164 in SG A,139 in SG B, and 125 in SG C. 'The RPC confirmation was obtained for 417 TSP ODSCC indications among 1231 bobbin flaw signals reponed. It is considered that I only those intersections which exhibit ODSCC detectable with the RPC probe warrant , scrutiny with respect to the repair criteria; however to assure realistic assessment of the observed data, TSP bobbin indications reported as exceeding the 40% Tech. Spec.~ repair criterion are regarded as RPC confirmed if they. were not actually RPC tested. ' The impact of
" Appendix A"-type guidelines in conjunction with application ofInterim Plugging Criteria is expected to be an increase mainly in the number of small voltage (< 1 volt) indications observed during the next inspection.
As described in Section 7.1 the axial distribution of the TSP ODSCC indications exhibits the strong correlation with distance from the hot leg tubesheet. Approximately 65% of the TSP , bobbin indications were observed at the IH level, almost 26% at the 2E level, only about 7% at 3H, and 2% at the 4H elevation; a scattering of indications were found at the SH (4) and 7H (5) levels. The bobbin amplitude distributions associated with these indications are : presented with the corresponding cumulative probability curves in Figures 7-2 to 7-5 for the individual SG's and the composite of all three; Table 7-3 lists the distributions of the bobbin . voltage values for each SG individually, as well as for the combined population; the indications counted in this table include those for which no 1991 re-analysis was possible. The largest voltage indication reported was (3.60 volts) was found in SG A; this tube was ; continued in service based on the Tech. Spec. plugging criteria, since its indicated depth was ;
~
less than 40%. The bobbin amplitude distribution for those indications confirmed by RPC testing is given in Figure 7-6. RPC detection reflects the existence of an array of short cracks. l typical of ODSCC indications which have some individual cracks long enough and deep enough to be detected by the RPC probe. Table 7-4 provides detailed RPC confirmation statistics as a function of bobbin signal voltage for each of the Sgs, as well as the composite [ of all three steam generators. t i 7.1.2 Prior Inspections: 1991 (EOC-8) and 1989 (EOC-7) ; t The first tube repairs performed because of TSP ODSCC indications occurred in December, ! 1987 (EOC-6) at which time 8 tubes were plugged. The full scope inspection performed at ; EOC-7 in September 1989,1.20 Effective Full Power Years (EFPY) since the previous t inspection, resulted in repair of 117 tubes for TSP ODSCC; in this inspection distoned support signals were allowed to remain in service, and signals with low signal to noise ratios ; were not reported as flaws. This practice was modified after the industry became aware of ! the potential severity of ODSCC indications in TSP intersections which displayed flaw l characteristics distorted by noise or competing artifact signals. The voltage growth rate ; determined for Cycle 7 was 44% on average, among the higher of similar plants' growth ' rates , for TSP ODSCC. The largest TSP ODSCC indication had a signal amplitude of 3.54 volts l i The field inspection results obtained during the EOC-8 inspection (April 1991) indicate a total l of 1525 TSP intersections were identified as exhibiting possible ODSCC signals; of this total l 672 were found in SG A,418 in SG B, and 435 in SG C. Figure 7-7 presents the numerical j distribution of the TSP indications by elevation (TSP #) above the tubesheet. Tubes , l l , 7-2 ! l
- , .. . - - - - - - = - - . , - - - - - - ~ . - - . - - . . - . - - - - , - - - ~ - - - - - , - - -
exhibiting percent indications exceeding 40% throughwall depth were generally plugged without subjecting the TSP indications to RPC confirmatory testing, and those percent indications less than 40% were typically not retested with the RPC probe. The total number of TSP intersections subjected to RPC testing added up to 1135, mainly DSI's (distorted support indications), distributed 655 in SG A,350 in SG B, and 230 in SG C; some intersections were tested at the request of the EC analyst to clarify difficult signals, and some were tested as part of the tube pull candidates selection process. (Two tubes, RllC48 and R16C60, from SG A were pulled to characterize indications above the tubesheet and at tube support plate intersections.) About 71% of the indications were observed at the first support plate. Figure 7-8 gives the frequency distribution of the 1991 bobbin coil signal amplitudes as a histogram together with the cumulative probability curve. Half of the reported indict,tions were less than I volt in amplitude, and more than 90% were below 2 volts. The maximum indication amplitude reported was 3.91 volts. Histograms of the bobbin voltages in each SG are shown in Figure 7-9,710, and 7-11. The statistical abstract for the 1991 TSP ODSCC indications is given in Table 7 5; Figure 7-12 shows the comparison among the voltage distributions for the three SG's, illustrating the predominance of SG A as the most affected of the three. On the basis of Tech. Spec. criteria and RPC probe confirmation of TSP DSI indications, 734 tubes were repaired during the EOC-8 inspection for TSP ODSCC, Cycle 8 operations accrued 1.07 EFPY, a run time about 10% less than the Cycle 7 cumulative full power operation. The increase in repairable tubes resulted in part from RPC confirmatory testing of the DSI signals, many of which were found to exhibit the crack like (axial and linear) l indications characteristic of ODSCC. 7.2 Growth Rates from Prior Cycles Eddy current inspection results from the December 1987 (EOC-6), September 1989(EOC-7), and April 1991(EOC-8) inspections at Beaver Valley-1 have been re-evaluated to assess the progression of ODSCC at the TSPs. He objective of the review was to assess the progression of ODSCC in the Beaver Valley-1 steam generators over the Cycle 7 and Cycle 8 operating periods. 954 indications from the tubes plugged during the 1991 inspection were traced back to the 1989 and 1987 inspections to assess whether they could be observed in light of the 1991 data and if so, to obtain the bobbin signal evaluation. The results of this review were used to obtain growth rates of the TSP indications As is evident from the Table 7-1 summary of bobbin coil amplitudes over the last 3 cycles, the progression rate of the TSP ODSCC indications had begun to lessen during Cycle 8, but it was still substantial enough (19%) to contnbute to the increased population of indications observed during the EOC-8 inspection. Table 7-6 compares the growth distributions of Cycle 9 with the composite growth distributions from Cycles 7 and 8. The bobbin voltage amplitudes of the TSP indications during the 1989 inspection ranged from 0.17 to 3.54 volts with an average value of 0.95 volts. nese indications had amplitudes in the range of 0.04 to 3.03 volts during the 1987 inspection. It may be noted that virtually all f of these indications remained in service during Cycle 7 and Cycle 8. Growth in amplitude for l 7-3
each of the aese two cycles was determined for the cases where bobbin signal voltage data were available for at least two consecutive inspections; i.e., no assumption about the signal voltage for prior years was made if a flaw indication was not available. As a result, growth estimates for Cycle 8 were made for only 952 of the 954 indications studied in 1991 (two indications were not detectable during the reevaluation of the 1989 inspection data). Similarly, growth rates during Cycle 7 could be estimated for only 918 of the 954 indications from 1991. Of the 36 indications without growth estimates during Cycle 7,29 had no detectable flaw signal in 1987 and/or 1989 and for the other seven indications, the eddy current tape from 1987 was not available during this reevaluation. A frequency distribution (in percent of each steam generator indications) of voltage growth in each of the three steam generators during Cycle 8 is shown in Figure 7-13. The growth rate distribution is substantially similar among the three steam generators. The mode (interval of highest frequency) of the amplitude growth is in the range of 0.1 to 0.2 volt. Figure 7-14 shows a plot of the growth in amplitude from 1989 to 1991 as a function of the l 1989 amplitude for the TSP indications in each of the steam generators. It may be noted that l the amplitude growth ranged from about -0.9 to +1.57 volts. The negative growths (and possibly some of the high positive growth values) result from the uncertainties in the eddy ! current inspection and data evaluation discussed above. Overall, the distribution of ! amplitudes and their growths appear reasonable, based on experience with data from other l plants. Figure 7-15 shows the growth in amplitude Cycle 7 as a function of the beginning of cycle (BOC) bobbin amplitude. The data from Cycles 6 and 7 appear quite similar. Figure 7-16 shows a frequency distribution of voltage growths during Cycle 8. The upper ends of the ranges are displayed on the X-axis. The cumulative frequency distribution in , percent is also displayed in the figure, as an "S" curve. It may be noted that most of the indications had growth rates between 0.0 and 0.3 volt per cycle. Only 5 of the 952 growth rates were greater than 1 volt / cycle and all (100%) of the indications had growth rates less than 1.57 volts per cycle. The frequency distribution of voltage growth during Cycle 7 is j shown in Figure 7-17. These results are quite similar to those from Cycle 8. The average growth in amplitude for indications in each steam generator was calculated for the three cycles. This is displayed in Table 7-7 along with the overall average which includes all steam generators. The number of indications used in the calculation of the average is also shown in the table. Some of the variation in the growth rates is attributable to the uncertainty in the voltage indications from prior inspections. The overall average growth rates of TSP indications during Cycles 7 and 8 were 0.29 and 0.18 volt, respectively. The standard deviation associated with the overall average growths in amplitude during Cycles 7 and 8 l were 0.27 volt and 0.24 volt, respectively. As discussed above, part of the scatter results from the uncertainty in the eddy current tests and the data evaluation and the remaining from the variability in growth between indications. Overall, it may be noted that the average amplitude growths is low, being in the range of 0.1 to 0.3 volt per cycle. Experience with the data from one European plant indicates that the percent growth in amplitude tends to be stable, i.e., independent of amplitude (however, this is not supported by 7-4
data from several other domestic units). The European data suggests that the small amplitude 1 indications grow by smaller voltages and that large amplitude signals are more likely to grow l by a larger voltage during the subsequent cycle. Percent growth rate is calculated by taking ( the ratio of the growth in amplitude during an operating cycle and the amplitude of the signal ) during the prior inspection. Figure 7-18 shows a plot of the percent growth in amplitude vs i BOC bobbin voltage for Cycle 8 for each of the steam generators. It may be noted that the high percent growth rates are observed only at low amplitudes. Two factors contribute to this: 1) at low signal amplitudes, the uncertainty in the signal analysis may be higher, and 2) since the BOC amplitude is in the denominator in the percent growth calculation, the percent I growth value is magnified for the low amplitude (BOC) indication. Percent growth rates l during Cycle 7 are plotted in Figure 7-19 as a function of the BOC amplitude. The population of the indications is the same for the data shown in these figures for the two cycles. Hence the BOC amplitudes are lower for Cycle 7 than those for the next operating I cycle. Further, as seen in Table 7-1, the average growth rate was higher during Cycle 7 than during Cycle 8. As a result, indications with higher percent growths are observed in Cycle 7 at the very low BOC amplitudes. The average percent growth rates of all the indications from the two operating cycles were calculated for Beaver Valley-l. This is displayed in Table 7-1. For the Cycle 7 and Cycle 8 data, the average growth rate of TSP indication voltage was 44% and 19% respectively. Thus, the percent growth rate in amplitude showed a decreasing trend during these two cycles. It was noted before that the percent growth rate of amplitude is lower at higher BOC amplitudes (see Figures 7-15 and 7-16). This observation is typical of all domestic plants evaluated by Westinghot" to date. Thus, an overall average of percent growth rate may have a strong upward bias due to the small amplitude signals. To assess the impact of f.is factor, average p.ercent growth rates were calculated for two different BOC amplitude ranges: above and below 0.75 volts. The results are displayed in Table 7-1. For BOC amplitudes below 0.75 volts, the average percent growth rate for the 1989-91 cycle was 27%, whereas the average for BOC amplitudes equaling or exceeding 0.75 volts was 16%. A similar difference is noted for Cycle 7, when the averages of the two ranges were 54% and 34%, respectively. This significant difference must be taken into account in the development of the plugging criteria. The standard deviations associated with the averages are listed in Table 7-1. 7.3 Growth Rates for Cycle 9 (1991 - 1993) The progression of ODSCC indications at the tube support plates is determined by comparison of the signal amplitudes measured in identical fashion at the location cfinterest for each of the reported indications from the 1993 inspection against the re-evaluated amplitude assigned to suspected Daw signals previously or newly observed in the 1991 EC tape records at the corresponding location. The quality of the prior year signal may reflect the reason for its not having been reported; e.g. a clean absence of detectable degradation (NDD), the presence of interference such as denting, excessive noise, permeability signals, or TSP mix residuals attributed to alloy property changes induced by service exposure. Altemately,if the EC signal interpretation guidelines, as written or as implemented, have changed significantly since 7-5
' the prior inspection, a new population of flaw indications may be founil in the re-evaluation process. 'Ihe knowledge that the location being reviewed has exhibited a flaw indication in l the later inspection may cause keener sensitivity to subtle flaw behavior.
The determination of amplitude growth based on re-evaluating prior inspection data has been j used consistently for all the applications of the Interim Plugging Criteria for TSP ODSCC. This method identifies the largest changes, which usually result in repair of the specific tubes
.- involved owing to actual growth, and very conservative average growth values may be reported. Because of the repairs and the possible observation of er.tirely new ODSCC indications, differences in the successive growth rates for the indication populations may be evident from inspection to inspection. Changes in the crevice chemical environment can i produce marked effects on ODSCC progression, resulting in potential uncertaimy in assessing growth trends. Growth determination on a fixed population of tubes over several cycles
- might yield a more consistent evaluation, but the requirement to repair larger amplitude flaws results in under-representation of the most serious flaws in prior inspections in a population j chosen from the latest inspection, resulting in possible underestimation of average prior cycle 1 growth. For the Beaver Valley Unit I case, the 1991-1993 growth evaluation represents the '
behavior of tubes continued in service on the basis of acceptable or non-detected degradation in 1991; the ODSCC progression which preceded the 1991 inspection can be fairly represented by constructing a population of tubes which combines the flaws retroactively identified during the 1991-1993 growth study with the tubes identified and repaired during the 1991 inspection, followed by re-evaluation of the 1989 EC data for this population. Similarly [ the pre-1989 growth rate is determined by re-evaluating the 1987 EC data for the combination , of 1989-1991 population with the tubes identified and repaired in 1987. Table 7-1 presentt ; the current cycle results together with those reported for the prior cycles in WCAP-13579; Table 7-1 also provides the summary inforraation on per cycle growth rates expressed as [ percent of the BOC average amplitude with the indications segregated as to those < 0.75 volts and those :t 0.75 volts. The distribution of the growth rates, expressed as the voltage difference in the amplitudes for two inspections is tabulated (Table 7-6 ) in 0.1 volt bins up to 1.2 volts; for each bin the l number of indications compared is entered together with the corresponding cumulative l probability value. In Table 7-7 the voltage growth average values reported on a per cycle basis, and on a SG by SG basis for each of the last 3 cycles, are presented to facilitate , comparison over the this period. The voltage growth histogram for Cycle 9 is presented as a [ composite for 3 Sgs in Figure 7-20. The average BOC amplitude for this cycle was 0.57 f volts, with very little difference in the averages for the three SG's; the average growth was i 0.09 volts. The maximum SG average growth observed was 0.14 volts in SG A,25% per cycle based on the average BOC amplitude of 0.57 volts. The largest individual growth,1.18 l volts, was also observed in SG A, and Table 7-8 presents the largest individual growth l 1 observations for the cycle. Figure 7-21 gives the SG A growth rates for Cycle 9 in histogram form together with the associated cumulative distribution curve. As has been the case in i other instances in which the Interim Plugging Criteria have been applied, the growth rate of ! the indications with appreciable amplitudes, i.e., those from 0.75 volts and up,is only a fraction of the overall average growth rate,5% for this group compared to 14% for the ; composite population or 25% for SG A. 7-6 ; 1 _ . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __.___- ._- . _ _ _ _ - - . _ ~ . _ .
The giowth rate trend derived from the last 3 cycles of data shows that the progression of ODSCC in the TSPs at Beaver Valley Unit 1 is comparable to growth rates at other domestic plants and well below the more rapid growth rates observed in European plants. No tube leakage events due to TSP ODSCC have occurred in Beaver Valley Unit I nor in any of the other U.S. plants affected by this phenomenon in the absence of denting; this is consistent with the generally low signal amplitudes associated with TSP ODSCC in most domestic plants. The maximum signal amplitude observed in Beaver Valley Unit 1,3.60 volts in SG A, is below the voltages reported in other domestic plants, ranging as high as 22 volts in one case. 7.4 Voltage Distributions for Example SLB Analyses SLB leak rate and tube burst probability analyses are provided in Section 8.4 to demonstrate methodology and to assess the magnitude of potential leakage following implementation for Cycle 11 of an IPC repair limit of 1.0 or 2.0 volts. Since voltage growth rates have been generally improving over the last few cycles, it is reasonable or conservative to estimate the potential EOC-Il leak rate by estimating the EOC-10 leak rate assuming an IPC of 2.0 volt , was implemented at BOC-10. For this purpose, voltage distributions at BOC-10 are developed herein assuming a 2.0 volt IPC. For general comparisons, the BOC-10 distributions are also developed for the Technical Specification repair basis (40% depth criteria) actually implemented at EOC-9. Data are also provided to define the BOC-10 voltage distribution assuming a 1.0 volt IPC had been implemented. To assess methodology for defining BOC distributions for IPC/APC applications, three methods are being evaluated against actual distributions for plants that have previously implemented an IPC. The three methods differ in the methodology for accounting for undetected indications or new indications and the potential for RPC NDD indications left in service to become flaws at the end of the operating cycle. All three methods are evaluated for the Beaver Valley I analyses of this report. The three methods are the draft NUREG-1477 method of applying a POD (Probability of Detection) = 0.6 independent of voltage, an application of POD = 1.0 and an alternate method called the new indication method. The draft NUREG method accounts for undetected and new indications through the very conservative POD and further conservatively considers all RPC NDD indications as real flaws with no weighting factor for the likelihood of an NDD indication becoming a detectable flaw at the end of the cycle. The POD = 1.0 method does not directly account for undetected indications but assumes that the RPC NDD indications left in service compensate for significant new indications as well as the small fraction of NDD indications that become flaws at the end of the cycle. The new indication method more directly accounts for new or undetected indications and the likelihood that RPC NDD indications become flaws at the end of the cycle. The new indication method is based on the expectation that the number and distribution of new indications (indications not reported in the prior inspection) found in the last inspection (EOC-9 for this example) represent the number expected over the next operating cycle. 'Ihe population of new indications considered significant for leakage and burst considerations at the EOC is the population of RPC confirmed bobbin indications. This represents the significant population that were not 7-7
1 detected at the prior inspection (EOC-8 for this example). To define tiie BOC-10 distribution l for new indications, the new indications at EOC-9 are evaluated at the BOC-9 or EOC-8 voltages using the voltages obtained from the Cycle 9 growth evaluation, his distribution for new indications is added to the detected indications left in service at BOC-10. He likelihood that RPC NDD indications left in service become confirmed indications at EOC can be evaluated from the inspection results. As shown below, the fraction of RPC NDD indications left in service at BOC 9 that became confirmed RPC indications at EOC-9 was 27.2%. ne new indication method accounts for this small fraction of NDD indications , becoming EOC flaws by multiplying the number of RPC NDD indications left in service for each BOC voltage bin by a factor of 0.3 which bounds the actual confirmation rate. This ' methodology for the new indication method utilizes the prior cycle inspection results to obtain the best estimate for RPC confirmed indications at the next EOC. S/G A had the most indications and would represent the limiting S/G for SLB analyses. : Table 7-9 summarizes the development of the BOC-10 distributions for both an assumed IPC of 2.0 volts and the actual indications left in service for both a POD of 0.6 for the draft i NUREG-1477 methodology and for a POD = 1.0. For a 2.0 volt IPC, it is seen that a POD of 0.6 results in 939 indications in service at the BOC while the POD of 1.0 results in 558 ' BOC indications. De actual numbers at BOC for PODS of 0.6 and 1.0 are 747 and 366 respectively. From Table 7-9, it is seen that if a 2.0 volt IPC had been in place for Cycle 10, i the number of plugged indications would have been reduced from 205 to about 13. He relatively large number of actual indications left in service results fro.n the large number of - , RPC NDD indications (404) found in the EOC inspection. This large number of NDD , indications left in service results in conservative projections for the next cycle since both POD values assume all the NDD indications become flaw like at the EOC. He four BOC distributions of the last columns of Table 7-9 are used in Section 8.4 to developed projected EOC voltage distributions and SLB leak rates. ; Table 7-10 develops the BOC voltage distributions for the new indication methodology with ' an assumed IPC of 2.0 volts. The number of new (not reported at the EOC-8 inspection) indications found at EOC-9 are shown in the second column of the table based on the EOC-8 (1991) voltages for these indications from the voltage growth evaluation. Typically a number ; of prior inspection, potential bobbin indications are not found at the end of the cycle. The : distribution for these indications is shown in the third column of the table and the net number l of new indications is the difference between the new indications and the prior indications not ! l found. Only about 30% (see Table 7-11) of the new bobbin indications were RPC confirmed. The new indication at BOC column of Table 7-10 represents the net number of new indications that were RPC confirmed or not RPC inspected. This represents the new indication distribution at BOC-10 for adding to the indications left in service. i Table 7-11 summarizes the 1993 S/G A RPC confirmation rate separated by prior bobbin indications having < 40% depth in 1991 and not RPC inspected, prior RPC NDD indications left in service in 1991 and new indications in 1993. It is seen from Table 7-11 that the RPC NDD indications left in service have the lowest 1993 confirmation rate of 27.2% which is [ slightly lower than the 30% confirmation inte found for new indications. The indications left i in service are developed in Table 7-10 as the sum of RPC confirmed plus not tested 7-8 t l-
indications and RPC NDD indications multiplied by 0.3 (expected Cycle 10 RPC confirmation rate based on Cycle 9 results of Table 7-11) as reduced by the number of plugged indications. The indications at BOC column represents the number of detected indications left in service including an adjustment for RPC NDD indications. The last column of Table 7-10 provides the total BOC indications for an assumed 2.0 volt IPC as obtained by adding the new indication at BOC and the prior indication at BOC columns. For the assumed 2.0 volt IPC,the BOC distribution is comprised of 381 indications including a projected 106 new indications and an effective 275 indications left in service. The 381 indicati.ons represents a projection of the estimated number of RPC confirmed indications at EOC assuming a 2.0 volt IPC was implemented. A similar distribution for the new indication methodology was developed for the actual indications left in service and resulted in 216 indications at BOC. These distributions are also used in Section 8.4 to develop projected EOC voltage distributions and SLB leak rates. 1 The BOC-10 distributions for a given analysis method or POD differ primarily in the number of plugged tubes for the various assumed repair limits. The BOC distributions for an j l assumed IPC repair limit of 1.0 volt can then be obtained from the data of Tables 7-9 and 7-10 based on the changes in tube plugging for this repair limit. Table 7-12 summarizes the estimated bobbin indication plugging for the assumed 1.0 and 2.0 volt IPCs and the actual plugging for the applied 40% repair limit. It is seen that the 2.0 volt IPC,1.0 volt IPC and 40% depth repair bases lead to 13,54 and 205 indications plugged, respectively. Due to the large number of indications below 1 volt plugged for the 40% repair limit, a 1.0 volt IPC would leave 151 more indications in service than the 40% depth limit as compared to 192 more indications in service for the 2.0 volt IPC. 7-9 l
l I I Table 7-1 Percent Voltage Growth Per Cycle: Beaver Valley Unit 1 , BOC Voltage Voltage Growth Average AV Number ofIndications Ave. Std. Dev Ave. Std. Dev %/ Cycle Cycle 9 Entire Range 1125 0.57 0.27 0.09 0.23 16% 1991- 1993 Veoc<.75 918 0.47 0.14 0.09 020 19%
~
Veoc2.75 207 1.02 0.30 0.06 0.31 6% Cycle 8 Entire Range 952 0.95 0.44 0.18 024 19% l 1989-1991 Vecc<.75 366 0.58 0.12 0.16 0.19 28% Vece2.75 586 1.18 0.41 0.19 0.26 16% Cycle 7 Entire Range 918 0.66 0.31 0.29 0.27 44 % 1987-1989 Vecc<.75 622 0.49 0.15 0.27 022 55 % . Vecch .75 296 1.01 0.28 0.34 i 0.33 34 % . t I l ' l i I l 75M4 DLW941P.XLS Table 7-1 % Growth per cycle _ _ m - _ _ _ _ _ _ _ _ _ _ -
Table 7-2 Beaver Valley Unit i 1993 Distribution of TSP Bobbin Probe ODSCC Indications - Laboratory Re-evaluated Data S/G A S/G B S/G C All S/G's i Na W Met As Ave. Not d MUL Na W Met Net d tiet osuunan % venage venage 0,=ei m venage Ave Veenge A=ut osene *wsomnons vanage Aim vaange 4.e ome eummaans veense h venage Amat emesi , 1H 300 3 60 0.77 0.17 229 1.95 0.80 0.00 197 2.20 0 64 0 04 795 3 80 0 Se &OS 2H 150 1 ee 0 59 R10 se 1.2e Oss 0.02 7s 1 02 ast 0 04 314 t es O so aer *i 3H 37 1 85 0 68 0 14 29 2.00 0.50 0 01 16 0.92 0.de 0 05 82 2.00 0 02 SW 4H 9 0.99 0 S3 0 06 12 0 83 0.00 0.03 $ 0.67 0 44 4 08 26 0 90 0.53 SW SH 4 0 74 0 63 0.12 3 0.22 0.22 4 24 1 8 0 74 0 S3 SW SH O O 1 1 7H 3 0 33 0 29 O 05 0 2 0.26 ats 4 02 5 0.33 0.23 4 00 S72 381 298 1231 l I 1 i 1 I I l l 7/5/94 1 DLW94tP.XLS , l Table 7-2 TSP Ind. Diet i ____________________j
i l Table 7-3 . Beaver Valley Unit 1 Cumulative Probability Distributions for Bobbin, Amplitudes 1993 Laboratorf Re-evaluation S/G A S/G B S/G C Combined Data Voltage # obs CPDF # obs CPDF # obs CPDF # obs CPDF 0.1 0 0.00 0 0.00 0 0.00' O 0.00 0.2 12 2.10 8 2.22 5 1.68 25 2.03 0.3 34 8.04 35 11.91 17 7.38 86 9.02 0.4 63 19.06 62 29.09 34 18.79 159 21.93 0.5 68 30.94 82 51.80 48 34.90 198 38.02 0.6 84 45.63 59 68.14 67 57.38 210 55.08 0.7 80 59.62 39 78.95 53 75.17 172 69.05 0.8 61 70.28 24 85.60 29 84.90 114 78.31 0.9 48 78.67 18 90.58 20 91.61 86 85.30 l 1 32 84.27 15 94.74 9 94.63 56 89.85 1.1 25 88.64 5 96.12 7 96.98 37 92.85 1.2 14 91.08 4 97.23 4 98.32 22 94.64 1.3 12 93.18 6 98.89 2 98.99 20 96.26 1.4 6 94.23 1 99.17 0 98.99 7 96.83 1.5 8 95.63 1 99.45 1 99.33 10 97.64 1.6 3 96.15 0 99.45 0 99.33 3 97.89 1.7 7 97.38 0 99.45 0 99.33 7 98.46 1.8 5 98.25 0 99.45 0 99.33 5 98.86 1.9 2 98.60 0 99.45 0 99.33 2 99.03 2 1 98.78 2 100.00 1 99.66 4 99.35 2.2 0 98.78 0 100.00 1 100.00 1 99.43 2.4 2 99.13 0 100.00 0 100.00 2 99.59 2.6 1 99.30 0 100.00 0 100.00 1 99.68 2.8 2 99.65 0 100.00 0 100.00 2 99.84 3 1 99.83 0 100.00 0 100.00 1 99.92 3.2 0 99.83 0 100.00 0 100.00 0 99.92 3.4 0 99.83 0 100.00 0 100.00 0 99.92 3.6 1 100.00 0 100.00 0 100.00 1 100.00 572 361 298 1231 7/5/94 DLW94tP.XLS Tcbb 7 3 Signal Spectra 7 '12
Table 7-4 Number of RPC Confirmed Indications and Number of Tubes Plugged for Beaver Valley Unit 1 in 1993 [ Laboratory Re-evaluation S/G C All S/G's S/G A S/G B No. of Ind. No. of Ind. No. cf Ind. No. of Ind. No. of No.RPC Removed from No. of No. RPC Removed No.of No. RPC Remcved No. of No.RPC Removed Indications Confirmed from SeMee Signal Voltage Indications Confirmed from Service Indications Confirmed from Service Indications Confirmed SeMee 0.1 5 8 8 2 3 5 2 2 25 0.2 12 1 :3 13 17 3 5 86 18 35 0.3 34 4 :17 35 11 22 34 15 15 159 41 82 0.4 63 11 .25 62 15 48 19 19 198 63 89 0.5 68 10 28 82 34 42 17 67 29 30 210 69 78 i 18 0.6 84 22 .31 59 l 15 17 53 29 30 172 64 69 ~ 0.7 80 20 22 39 8 29 8 12 114 38 46 l 0.8 61 21 !26 24 9 9 20 8 9 86 33 34 0.9 48 17 16 18 8 3 6 9 6 7 56 21 26 1 32 12 13 15 7 3 3 37 14 12 1.1 25 10 8 5 1 1 4 4 4 4 22 11 11 l 1.2 14 4 3 4 3 5 5 2 2 2 20 13 8 1.3 12 6 1 6 7 5 1 1.4 6 4 0 1 1 1 1 1 1 1 10 4 5 1.5 8 2 3 1 1 3 2 2 1.6 3 2 2 7 4 2 1.7 7 4 2 5 4 3 1.8 5 4 3 2 1 0 1.9 2 1 0 2 1 1 4' 3 2 2 1 0 0 2 1 1 1 0 1 1 0 1 2.2 2 1 1 2.4 2 1 1 2 1 1 2.6 2 1 1 1 1 0 2.8 1 1 0 1 1 0 3 1 1 0 0 0 0 3.2 0 0 0 3.4 - 0 1 0 1 3.6 1 1 159 206 361 128 150 298 130 141 1231 417 497 Totals 572 DLW94tP.XLS 715I9 4 Table 7-4 ind. Stats.
f Table 7-5 .. Beaver Valley Unit 1 1991 Suppart Plate indication Statistical Abstract S/G B SMB C ComtWned . StG A No.obs - -;-# No.obs e-;-? No.obs ---E No.obs 0 0.00 0 0.00 0 0.00 0 0 0.00 I 0.24 2 0.46 5 0.38 0.2 2 0.30 1 6.22 16 4.14 108 7.41 0.4 67 10.27 25 104 31.10 99 26.90 379 32.26 0.6 176 36.46 94 53.59 125 55.63 377 56.98 0.8 158 59.97 ' 81 72.97 79 73.79 263 74.23 1 103 75.30 42 83.01 31 80.92 141 83.48 1.2 68 85.42 25 89.00 39 89.89 102 90.16 1.4 38 91.07 19 93.54 16 93.56 55 93.77 1.6 20 94.05 10 95.93 7 95.17 34 98.00 1.8 17 96.58 97.61 7 96.78 23 97.51 2 9 97.92 7 2 98.09 4 97.70 11 98.23 l 2.2 5 98.66 4 99.04 4 98.62 11 98.95 f 2.4 3 99.11 4 100.00 2 99.08 7 99.41 2.6 1 99.26 0 100.00 3 99.77 6 99.80 2.8 3 99.70 0 100.00 0 99.77 1 99.87 3 1 99.85 ' 0 100.00 0 99.77 1 99.93 3.2 1 100.00 0 100.00 0 99.77 0 99.93 3.4 0 100.00 0 100.00 0 99.77 0 99.93 3.6 0 100.00 0 100.00 0 99.77 0 99.93 3.8 0 100.00 0 100.00 1 100.00 1 100.00 4 0 100 ' 418 435 1525 Totals 672 i t I i 7 - 14 .
Table 7 8 Beaver Vallely Unit 1 Cumulative Probability Distributions for Voltage Growth l 1991 to 1993 Laboratory Re-evaluation l 1987-1989 1989-1991 S/G A S/G B SIG C Combined Data
# obs CPDF # obs CPDF # obs CPDF # obs CPDF # obs CPDF # obs CPDF Voltage 9.37 195 20.48 150 26.27 146 50.17 106 40.30 402 35.73 0 86 22.33 172 38.55 129 48.86 60 70.79 78 69.96 267 59.47 .
0.1 119 40.96 184 57.88 111 68.30 48 87.29 39 84.79 198 77.07 0.2 171 57.84 154 74.05 62 79.16 19 93.81 23 93.54 104 86.31 0.3 155 150 74.18 114 86.03 45 87.04 9 96.91 11 97.72 65 92.09 0.4 , 82 83.12 59 92.23 22 90.89 6 98.97 4 99.24 32 94.93 l 0.5 0.6 55 89.11 28 95.17 22 94.75 2 99.66 1 99.62 '25 97.16 0.7 32 92.59 20 97.27 7 95.97 0 99.66 1 100.00 8 97.87 0.8 20 94.77 12 98.53 9 97.55 1 100.00 0 100.00 10 98.76 i 0.9 21 97.06 6 99.16 8 98.95 0 100.00 0 100.00 8 99.47 1 8 97.93 3 99.47 4 99.65 0 100.00 0 100.00 4 99.82 1.1 7 98.69 1 99.58 0 99.65 0 100.00 0 100.00 0 99.82 1.2 4 99.13 0 99.58 2 100.00 0 100.00 0 100.00 2 100.00 1.3 4 99.56 1 99.68 0 100.00 0 100.00 0 100.00 0 100.00 1.4 1 99.67 1 99.79 0 100.00 0 100.00 0 100.00 0 100.00 - 1.5 2 99.89 1 99.89 0 100.00 0 100.00 0 100.00 0 100.00 1.6 0 99.89 1 100.00 0 100.00 0 100.00 0 100.00 0 100.00 1.7 0 99.89 100.00 0 100.00 0 100.00 0 100.00 0 100.00 1.8 0 99.89 100.00 0 100.00 0 100.00 0 100.00 0 100.00 1.9 0 99.89 100.00 0 100.00 0 100.00 0 100.00 0 100.00 j 2 0 99.89 100.00 0 100.00 0 100.00 0 100.00 0 100.00 , 2.1 1 100.00 100.00 0 100.00 0 100.00 0 100.00 0 100.00 918 952 571 291 283 1125 ;
..i i
i 71519 4 DLW944P.XLS i 3 29 FM Table 7 6 Growth Spectre
t Table 7-7 Voltage Growth Per Cycle for Beaver Valley Unit 1 SGs (1987 to 1993) Std.Dev. Ave. % St, No.ind. ' ! Ave. Std.Dev. No. ind. ' Ave. Cycle 0.14 0.25 25 0.57 0.3 571 A 572 0.19 2 19911o1993 0.25 291 0.01 361 0.57 B' 298 0.57 24 263 0.04 _Q J7 7 C 16 0.57 27 1125 0.09 $3 ' ibined 1231 0.15 0.26 11 0.96 0.47 433 A 433 23 1989io1991 272 0.21 0.22 272 0.93 0.39 8 247 0.19 02 20 747 0.94 0.44 C O 18 0.24 19 0.95 0.44 952' Contined 952 0.29 0.26 43 0.68 0.33 419 419 29 1987 to 1989 A 270 0.21 0.21 271 0.72 0.29 8 0.38 0.21 69 0.55 0.27 229 C ~ M9 O.29 0.27 44 0.66 0.31 918' Combined 919 Note 1: No..u of in6 cations included in the calcdation of the statistics ss (averspa'and standeri Note 2: This total differs from Gs lower than) the total nunter l of indications l found in ths 1991 '-1; becau: one or nere of the indications was not detectable fro,n prior irapedons 7 - 16 I 1
I Table 7-8 Summary of Larsest Bobbin Voltage Growth Rates for Beaver Valley Unit 1, 1991 - 1993 I 1993 1991 1993 91 93 Tube Bobbia Bobbia RPC Growth Dent et SG Row Colume Leesties Volts Volts Volts Volts Old 9dD A 10 36 lH _ 3.60 2.42 1.18 col A 7 11 IH 1.69 0.55 1.14 ces A 5 29 IH 2.80 1.81 0.99 Del A 22 36 1H 1.76 0.82 0.59 0.94 Del A* 10 31 IH 238 1.44 0.94 0s1 A 6 26 1H 2.92 1.99 0.63 0.93 Del A 5 54 2H 1.21 032 030 0.89 oei A 6 12 1H 137 0.49 034 0.88 oel A 10 18 IH 1.80 0.95 0.85 oei A 7 25 IH 1.87 1.03 0.36 0.84 os A 7 42 1H 135 0.52 0.40 0.83 col A 5 81 IH 2.49 1.67 0.82 0e A 5 42 IH 1.22 0.41 0.28 0.81 ces A 23 42 IH 1.17 036 0.42 0.81 Del A 5 54 IH 1.25 0.48 035 0.77 oei A 22 60 1H 1.74 0.97 0.71 0.77 oe A 4 35 1H 1.42 0.65 0.77 Del A 26 51 1H 1.40 0.64 0.76 0.76 Des B 3 12 IH 1.26 0.51 0.75 Des A 6 35 IH 1.28 0.53 0.75 osi ces l 7 - 17
l TABLE 7 9 EXAMPLE OF BOC DISTRIBUTIONS (POD = 0.6,1.0) FOR SLB ANALYSIS Number of BOC Indications Number RPC Actualin Service No. -No. IPC = 2.0 Volts of Confirmed POD POD POD No. Plugged POD Voltage Bobbin + Not RPC O.6 1.0 0.6 1.0 Tested NDD Plugged 2vIPC Bin Ind. 0 20.00 12.00 19.00 11.00 11 1 0.2 12 1 56.67 34.00 51.67 29.00 4 30 5 0 0.3 34 62.00 90.00 48.00 13 50 15 1 104.00 0.4 63 111.33 66.00 97.33 52.00 58 16 2 0.5 68 10 82.00 111.00 55.00 25 59 29 2 138.00 0.6 84 131.33 78.00 103.33 50.00 58 30 2 0.7 80 22 60.00 75.67 35.00 21 40 26 1 100.67 0.8 61 0 78.33 47.00 61.33 30.00 47 17 30 17 0.9 0 53.33 32.00 37.33 16.00 12 20 16 1.0 32 40.67 24.00 30.67 14.00 10 15 11 1 1.1 25 14.00 16.33 7.00 5 9 7 0 23.33 1.2 14 19.00 11.00 12.00 4.00 11- 6 6 8 1 1.3 4 0 10.00 6.00 6.00 2.00 1.4 6 5 1 10.33 5.00 6 3 0 13.33 8.00 1.5 8 2 3.00 1.00 2 0 5.00 3.00 1.6 3 2 1 6.67 2.00 3 5 0 11.67 7.00 1.7 7 4 4.33 1.00 4 0 8.33 5.00 1.8 5 4 1 2.00 2.33 1.00 1 1 0 3.33 1.9 2 1 1.00 1.67 1.00 0 1 O O 1.67 2.0 1 0.67 0.00 0.67 0.00 2.3 1 0 1 1 1.00 1 O O 1.67 1.00 1.67 2.4 1 0 1 0.00 0.67 0.00 0 1 i O.67 2.5 1 1 0 1.67 1.00 0.67 0.00 0 1 1 2.7 1 0 1.67 1.00 0.67 0.00 2.8 1 0 1 1 0.67 0.00 0 1 1 0.67 0.00 3.0 1 1 0 1.67 1.00 1.67 1.00 0 1 0 3.6 1 13 938.67 558.00 746.67 366.00_ 571 167 404 205 Total 7 - 18
f
;.i. -
TABLE 710 EXAMPLE OF SOC DISTRIBUTIONS (NTW INDICATION METHOD. 2.0v IPC) FOR SLB ANALYSIS
'93 New indications Beeed on '91 Voltnees '93 Indications Left in Service No. No. Not No. New ind. New ind. New RPC RPC No. Ind. Total Voltage New Prior ind. New RPC RPC Ind, at Conf. + NDO PluS9ed at BOC '
Bin Ind. (1) ItJR (2) Ind. (3) NDD Confirm BOC Not Test x 0.3 2vIPC BOC Ind.(4) O.2 20 20 17 2 3 1 3.3 0 4.3 7.3 0.3 66 2 64 53 12 12 4 9.0 0 13.0 25.0 0.4 84 6 78 59 23 23 13 15.0 1 27.0 50.0 0.5 86 12 74 65 21 21 10 17.4 2 25.4 46.4 0.6 48 11 37 34 13 13 25 17.7 2 40.7 53.7 0.7 33 2 31 18 15 15 22 17.4 2 37.4 52.4 0.8 19 2 17 12 7 7 21 12.0 1 32.0 39.0 0.b " 4 3 1 1 3 3 17 9.0 0 26.0 29.0 1.0 6 2 4 2 4 4 12 6.0 0 18.0 22.0 1.1 5 1 4 1 2 3 10 4.5 1 13.5 16.5 1.2 3 3 2 1 1 6 2.7 0 7.7 8.7 1.3 1 1 0 6 1.8 1 6.8 6.8 1.4 1 1 1 0 5 0.3 0 5.3 5.3 1.5 2 2 2 0 2 1.8 0 3.8 3.8 1.6 1 1 1 0 2 0.3 0 2.3 2.3 1.7 1 1 0 1 1 4 0.9 0 4.9 5.9 1.8 4 0.3 0 4.3 4.3 1.9 1 0.3 0 1.3 1.3 2.0 0 0.3 0 0.3 0.3 2.3 1 0.0 1 0.0 0.0 2.4 0 0.3 0 0.3 0.3 2.5 1 0.0 1 0.0 0.0 2.7 0 0.3 0 0.3 0.3 2.8 0 0.3 0 0.3 0.3 3.0 1 0.0 1 0.0 0.0 3.6 0 0.3 0 0.3 0.3 Total 379 42 337 268 104 106 167 121.21 13 275.2 381.2 NOTES:
- 1. Number of indications in '93 inspection and not reported in '91 inspection evaluated in '91 votts from vohage growth study.
- 2. Number of indications reported in '91 inspection as potential bobbin indications but not found in '93 inspection.1hese indications are sometimes called indications Not Reportable, or INRs.
- 3. Net number of new indications is the difference between the number of new
".ndications and prior indications not found. .
- 4. Total BOC indications is the sum of the columns for Ind. at BOC Mt in service plus the New Ind. at BQC.
l l 7 - 19
. . . . . . . .~.
1 TABLE 711
SUMMARY
OF '93 RPC CONFIRMATION Af) ' LUGGING B TYPE OF '91 PNDICATION Total No.RPC No.RPC % RPC No, Ind. Type of '91 Indication No. Ind. Inspected Confirmed Confirmed Plugged Prior '91 Bobbin - no RPC, depth < 40% 18 18 8 44.4 % 9 Prior '91 Bobbin DSI and RPC NDD 174 173 47 27.2 % 61 No '91 Bobbin Ind. - New Ind in '93 ; 379 372 104 30.0 % 135 Overall Totals 571 563 159 28.2 % 205 7 - 20
~ '
..=.
Table 7-12 Comparison of Tube Plugging at BOC-10 for 2.0 and 1.0 Volt IPCs and 40% Depth Limit l . Estimated Indications Plugged Actual Ind's. Voltage Plugged - J Bin 2.0 Volt IPC 1.0 Volt IPC 40% Depth '
- Repair 0.2 0 0 1 0.3 0 0 5 0.4 1 1 15 0.5 2 3 16 0.6 2 2 29 0.7 2 4 30 0.8 1 2 26 0.9 0 0 17 1.0 0 0 16 1:1 1 10 11 1.2 0 5 7-1.3 1 7 8 1.4 0 4 4 1.5 0 2 3 1.6 0 2 2 1.7 0 4 5
. 1.8 0 4 4 1.9 0 1 1 2.0 0 0 0 2.3 1 1 1 2.5 1 1 1 2.7 0 0 1 2.8 0 0 1
,3.0 1 1 1 Totals 13 54 205
Figure 7-1 Beaver Valley 11993 Distribution of TSP Indications vs Elevation 400 - 350 - . 300 - C l250-- li.2 E SIG A S 200 -. E SIG B
? eSs c E -
150 -- 100 - 30 0 ! t I I I i - 1 - - 1 01H 02H 03H 04H OSH 06H 07H Support Plate Elevation 71519 4 DLW94F.RS 4:18 PM Figue 71 . E
Figure 7-2 Beaver Valley 11993 Bobbin Amplitude Distribution - SIG A i I go . . - 100
- -- 90 80 -
i _. gQ 70 - ) -- 70 .f 8 -
/ $ .! -- 60 % .'*e i N
[ ~ 5"
) m No. ots i
(g 40 ] 0
-.--CPDF j -- 40 .E .
- s is
- z 5 !
30 -- E
-- 30 g 20 --
II __3 10 -- - 10 0 0 ., ; ; ; ;
;;;-;;;-ii;I;;I;I;E;; ;E; ;E;"; .
;" 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.4 2.8 3.2 3.6 Bobbin Amplitude (Volts) 8 Page1 i
h
i i 4 Figure 7-3 BeaverValley Unit 1 1993 Bobbin Amplitude Distribution S/G B 1
-- 100.00 90 -
- M00 80
-- 80.00 70 --
-- 70.00 .!
60 - U E E e -- e0.00 %
$ 50 -- E E 3c m No.obs
; -- 50.00 o 5 -+-CPDF 5 40 -- 5 n e E -- 40.00 3 z 3 30 - E
-- 30.00 g 20 -- -
- 20.00
~
10 -- O .. ; ; ; ; ; ; ; I;1;I;a;I;t=; ; ; ; ;E , ; ; ; ; .
-- 10.00 0.00 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.2 2.6 3 3.4 Bobbin Amplitude (Volts) -
Page1
d i 1
- Figure 7-4 BeaverValley 11993 Bobbin Amplitude Distribution SIG C 4
k 70 - - : : : : : : : ; * * * * * * * * ** 1 . 90 60 -- l 30 t c 50 -- -- 70 s
/
ti
. E -
.. ,9
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-- 20 I
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--10 0 .. -- ;
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; l Il 1.1
-; E :
1.3 1.5 1.7 1.9
- =:=:
2.2 2.8 3.2 3.6 o 0.1 , t Bobbin Amplitude (Volts) 715!9 4 DLW9er.XLS 4 31 PM Fig.74
1 I Figure 7-5 Beaver Valley 1 1993 Bobbin Amplitude Distribution All S/G's 250 -
- : : 0 0 0 0 0 0 0 0 # I P
-- 90 .
i
" 80 200 -
c
-- 70 .o -
o
. 8
$ 150 -- " 60 I0 Wu <-
5
-- 50
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E 100 -- --40 [
& 5 E i
-- 30 :s U ,
t
-- 20 I;;;;;E; 50 --
t
-- 10 0 -i ; ; ; ; ; ; ; ;";E;m;_;m;_;_;_;_;_; ; ;_ o 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.2 2.6 3 3.4 Bobbin Amplitude (Volts) 71519 4 DLW94r.XLS ;
4:40 PM Figue 75
~[
aa Number of Indications o a N u a m a u a e o
'1 1.1 ..
1.2 ~ n E 1'3 R
~
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& m 3.,1.7 5
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~ ; 3 3.2 "
[ {
- o 3.4 " .
3 j 3.6 .. T ' I . I
t Figure 7-7 l Beaver Valley-1 1991 Distribution of Bobbin Indications by TSP Elevaties - All SGs , 1200 1091 1000 - T E e s '
!O 800 - Issessil .
e a E 400 - ' 328 81 0 t 2 t M 3 t M 25 4 i 1 i 0 i 0 ' 1 5 6 7 M Plate Elevation
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. . . 1 I
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- - - - - - 4 - -
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Figure 7-12 Beaver Valley-1 1991 Distribution of TSP Bobbin Indications by Signal Amplitude - Comparison of Three SGs 180 160 1
~
140 lI 120 E e 100
, E S/G A 5 5 SIG B l
o i D StG C 3 80 . E , 60 40 i L i 20 0 :": . . .
= = = =
==== ==== ====-
Signal Amplitude e l ------__-__--- ----._-- -_---_ _ ____ _ _ _ _-- __ _ --
l l l BEAVER VALLEY UNIT 1 TSP INDICATION VOLTAGE GROWTH (1989-91) 2G i i 2} i , 1 m f- s
, 5 s t ,
~1
--,t , 1
, i 15- - ,
2 ,
- l
- l, l, b :1 : l ! l :! l 1& : l : l : l i
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0.3 * ,O1' 0.1 ' O,3 ' ' O,s ' ' O.7 ' ' O.9 ' '1.57
-0.2 0 0.2 0.4 0.6 0.8 1 UPPER END OF 89-91 VOLTAGE GROWTH RANGE
@ WG1A StG 1B M WG1c Figure 7-13. Percentage Distribution of Vottage Growths in each Steam Generator (1989-91 Cycle) l
BEAVER VALLEY UNIT 1~ TSP INDICATION VOLTAGE GROWTH (1989-91) 2 o S/G-1 A g a o Us I' o h
> ,, o a oa o *B o , o o n o 0.5- a au %
e , o o", 0- n m " % , , --- o -* - 0 00 M U o a D
-0. 5- ""
-1 . . . .
g g 0.5 1.5 2.5 BOC(1989) BOBBIN AMPLITUDE. VOLTS Figure 7-14. Growth in Bobbin Amplitudes During the 1989-91 Cyde
i .
~
BEAVER VALLEY UNIT 1 TSP INDICATION VOLTAGE GROWTH (1987-89) 2 l 1 S/G-1 A 15- o o a w a o b O 1- oo o no
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B a
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-1 . . . .
g g 0.6 1.5 2.5 BOC(1987) BOBBIN AMPLITUDE, VOLTS Figure 7-15. Growfn in Bobbin Amplitudes During the 1987-89 Cycle
l i BEAVER VALLEY UNIT 1 - TSP INDICATION VOLTAGE GROWTH (1989-91) 200 _ 100 184 , 180- 172 -90 '
?
160- 15 -80 140- f
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/
1 22% 120- 11 4 -60 100- -50 g 80- $ -40 60- -30 f 40- -20 24 20- 7
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-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 UPPER END OF 89-91 VOLTAGE GROWTH RANGE Figure 7-16. Histogram and Cumulatke Probability Distribution of Voltage Growth During the 1989-91 Cycle
- ~
BEAVER VALLEY UNIT 1 TSP INDICATION VOLTAGE GROWTH (1987-89) 200 100 180- 1 71 -90 r 1 60- 185 -80 l-l -70 1 140-120- r h -so 1 00- l f / @ l l/ 82 80- l/ -40 ! 66 60- / I y -30 40- 32 -20
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l Figure 717. Histogram and Cumulative Probability Distrbution of Voltage Growth ; During the 1987 89 Cycle t
BEAVER VALLEY UNIT 1 ~ TSP INDICAT10N VOLTAGE GROWTH (1989-91) 300 250- S/G 1 A 200-o 150- D o 100- o D o SP ao oo g D e o 0- ............, o . a . 9. . .% . . . .o . . . . . . . . .. . . . . g
-50 ,
?" , , ,
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BEAVER VALLEY UNIT 1 TSP INDICATION VOLTAGE GROWTH (1987-89) 300 o o o 8 /G'i ^ $ 250-b ' 200- oo o 16 o h 160- on "o f o, B o, g ooa 6 100- E o go b D a, o % 8 so- egl y*o o o
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Figure 7-20 Beaver Valley 1 TSP Indication Growth 1991 to 1993 All S/G's
- : : e - 100.00 450 - , ,
~~
400 -- f l
-- 80.00 l 350 -- )
C l
-- 70.00 .2 l 300 -- $
E E g -- 80.00 e
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] -*-CPDF l O !
3 200 --
$ -- 40.00 f )
E i 150 -- E
- 30.00 g i
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- 20.00 ,
50 -- __ 10.00 l l 0- -0.00 ! 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 Signal Progression (Volts) DLW948P.XL5 71519 4 5:30 PM Figne 720
.)
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4 ti 9f P s F 5 7 1 b D 72 5 oP .
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8.0 BEAVER VALLEY UNIT 1 IPC REPAIR CRITERIA 8.1 General Approach to the IPC Assessment The Beaver Valley Unit I repair criteria apply the EPRI ARC Guidelines of Reference 1 as modified to reflect the methodology detailed in the approved IPCs at Farley-1 and D. C. Cook-1 (Spring 1994) described in the associated NRC Safety Evaluation Reports (SER). _The IPCs apply the full APC repair limit as the bobbin voltage limit requiring repair, independent of RPC confirmation of the bobbin flaw indication. Between the IPC repair limit and the full APC repair limit, bobbin indications can be left in service if not confirmed by RPC inspection. The full APC repair limit following the EPRI guidelines is developed below. R. G.1.121 guidelines establish the structural limit as the more limiting of three times normal operating pressure differential (3 APuo) and 1.43 times the SLB pressure differential (1.43 APn3) at accident conditions. At normal operating conditions, the tube constraint provided by the TSP assures that 3 APyo burst capability is satisfied. At SLB conditions, the EPRI ARC are based on freespan indications under th'e conservative assumption that SLB TSP displacements uncover the ODSCC indications formed within the TSPs at normal operation. From Section 6.2, the bobbin voltage corresponding to 1.43 AP3t s = 3657 psi is 8.82 volts. The structural limit must be reduced by allowances for NDE uncertainties and growth. The EPRI ARC apply the NDE uncertainty (Section 7.3) at 95% uncertainty to obtain an allowance of 20.5% of the repair limit. For Beaver Valley, average voltage growth rates from tubes plugged for ODSCC indications at TSPs are bounded by a value of 20% per cycle over the last two operating cycles, as shown in Table 7-1. Cycle lengths in terms of EFPDs are not expected to significantly vary between the 1.35 years for Cycle 9 and Cycles 10 or 11. Cycle 9 had the longest operating period and the lowest growth rate of Cycles 7,8, or 9, for which growth data are given in Table 7-1. The lower growth rate of Cycle 9 indicates that growth progression is being controlled at Beaver Valley-l. A growth allowance of 40% per cycle is conservatively applied to develop the Beaver Valley-1 full APC repair limit. This allowance provides adequate margins for future variations in growth rates and cycle lengths. The full APC repair limit is obtained by dividing the structural limit of 8.82 volts by one plus 60.5% for the sum of the NDE uncertainty and growth allowance. Thus, the full APC repair limit is obtained as 5.5 volts. The Farley-1 and D. C. Cook-1 IPCs conservatively applied 3.6 volts for the full APC repair limit. Since the Beaver Valley-1 IPC follows this precedence, the 3.6 volt limit is also applied for the Beaver Valley-1 APC repair limit. This repair limit conservatively bounds the APC limit obtained by applying either the EPRI database, as described above, or the NRC database changes described in Section 5.1. 8.2 IPC Repair Criteria for Beaver Valley Unit 1 This section describes the IPC tube repair basis and the inspection / analysis to be performed to support the IPC. The Beaver Valley IPC are technically justified at a bounding 2.0 volt repair limit to be consistent with the IPC implemented at D. C. Cook-1 and Farley-1 in Spring 1994. 8-1
Margins associated.with a 1.0 vol' 'cepair limit consistent with the criteria of Draft NUREG-1477 are developed for the SLB analyses of Section 8.4, Beaver Vallev Interim Plunninn Criteria The IPC for ODSCC at TSPs can be summarized as follows:
- Tube Plueoine Criteria f
Tubes with bobbin flaw indications exceeding a 1.0 or 2.0 volt IPC voltage repair limit and 5 3.6 volts are plugged or repaired if confirmed as flaw indications by RPC i inspection. Bobbin flaw indications > 3.6 volts attributable to ODSCC are repaired - independent of RPC confirmation.
- Operating LfAkaat Limi18 i
Plant shutdown will be implemented if normal. operating leakage exceeds 150 gpd per SG (see Section 8.3). l SQLeakane Criterion , Projected end of cycle SLB leak _ rates from tubes left in service, including allowances for undetected indications, NDE uncertainties and crack growth, must be less than 6.6 . gpm for the SG in the faulted loop. If the allowable SLB leak limit is exceeded,- l additional tubes shall be repaired until the leakage limit is satisfied. The SLB leak : rate analysis applied for comparison with the allowable limit shall use the reference log logistic probability of leakage (POL) correlation. Sensitivity analyses .for_ SLB leakage shall be performed using the five additional POL correlations described in Section 6. , SMIuks_ Burst {ividelme The projected end of cycle SLB tube burst probability, including allowances for i undetected indications, NDE uncertainties and crack growth, shall be evaluated and l compared with the s 2.5x10 2 value found to be acceptable in NUREG 0844. Exclusions from Tube Plunnine Criteria ; Indications excluded from application of the IPC repair limits include: indications found by inspection (bobbin or RPC) to extend outside the TSP, indications not I attributable to ODSCC and circumferential indications. These indications shall be evaluated to the Technical Specification limits at 40% depth. Insoection Reauirements , Appendix A eddy current analysis guidelines and voltage normalization shall be applied in all inspections implementing IPC repair limits. 8-2
, . ,,,,,n..._ --
y & .ja_ h ,s b ,asmalti* 4i e du-a,a m,4mi--d 1e+- d 4.-# .4+6Me- 'M5, ~+ . , A ,=.J -<44-4 L 4 numam----ha2 -Aa 4
- f
;; '*: . Eddy current analysts shall be trained specifically to voltage sizing per the Appendix . :
A analysis guidelines, with at least lead analysts qualified to the industry standard Qualified Daia Analysis program, j
- ASME calibration standards cross-calibrated to the reference laboratory standard and i
_ probe wear standards shall be applied in IPC inspections. ;
. 100% bobbin coil inspection of all active tubes with a 0.720 inch diameter bobbin
- probe, for all hot leg TSP intersections and all cold leg intersections down to the lowest cold leg TSP where ODSCC indications have been identified. !
i
. RPC inspection of all bobbin indications greater than 1.5 volts for a 2.0 volt repair limit, or greater than 1.0 volt for a 1.0 volt repair limit, shall be performed to support . 1 axial ODSCC as the dominant tube degradation mechanism. l
- An RPC sample inspection shall be performed on at least 100 TSP intersections with dents or artifact / residual signals that could potentially mask a 1.0 or 2.0 volt bobbin signal, depending upon the repair limit specified in the plant's Technical Specification.-
The RPC sample program shall emphasize dented TSP intersections but include artifact signals that the analysts judge could mask a repairable indication. Any .RPC flaw indications in this sample will be plugged or repaired.
- The NRC'will be informed, prior to plant restart from the refueling outage, of any unexpected inspection findings relative to the assumed characteristics of the flaws at the TSP intersections. This includes any detectable OD circumferential indications or i detectable indications extending outside the thickness of the TSP. !
I The RPC inspection requirements for indications above 1.5 volts and for a minimum 100 intersection sample plan are consistent with the NRC resolution of draft NUREG-1477 issues as presented by the NRC at the NRC/ industry meeting of February 8,1994 on resolution of industry comments on the draft NUREG. These RPC, inspection guidelines were presented by : the NRC as part of the 2.0 volt IPC proposal. 8.3 Operating Leakage Limit Regulatory Guide 1.121 acceptance criteria for establishing operating leakage limits are based on leak-before-break (LBB) considerations, such that plant shutdown is initiated if the leakage associated with the longest permissible crack is exceeded. The longest permissible crack l length is the length that provides a factor of safety of 1.43 against bursting at SLB pressure l differentials. As noted in Section 6.2, a voltage amplitude of 8.82 volts for typical ODSCC cracks corresponds to meeting this tube burst requirement at the lower 95% prediction interval on the burst correlation. Altemate c' rack morphologies could correspond to 8.82 volts so that a unique crack length is not defined by the burst pressure-to-voltage correlation. Consequently, typical burst pressure versus throughwall crack length correlations are used below to define the " longest permissible crack" for evaluating operating leakage limits. i 8-3
. The CRACKFLO leakage model has been developed for single axial cracks and compared with leak rate test results from pulled tube and laboratory specimens. Fatigue crack and SCC leakage data have been used to compare predicted and measured leak rates. Generally good agreement is obtained between calculation and measurement with the spread of the data being somewhat greater for SCC cracks than for fatigue cracks. Figure 81 shows normal operation leak rates including uncertainties as a function of crack length for a pressure differential of 1460 psi, which represents current Beaver Valley 1 operating conditions. Potential future decreases in steam pressure would tend to increase normal operating leakage and increase _the leak before break margins described below. I The throughwall crack lengths resulting in tube burst at 1.43 times the SLB pressure differential (3657 psi) and SLB conditions (2560 psi) are about 0.54 and 0.84 inch, respectively, as shown in Figure 6 2. Nominal leakage at normal operating conditions for these crack lengths would range from about 0.34 to 3.0 gpm while -95% confidence level leak rates would range from about 0.05 to 0.5 gpm. Leak rate limits at the lower range near 0.05 gpm would cause undue restrictions on plant operation and result in unnecessary plant outages, radiation exposure and cost of repair. In addition, it is not feasible to satisfy LBB for all tubes by reducing the leak rate limit. Crevice & posits, the presence of small ligaments and irregular fracture faces can, in some cases, reduce leak rates such that LBB cannot be satisfied for all tubes by lowering leak rate limits. An operating leak rate of 150 gpd (~0.1 gpm) is implemented in conjunction with application of the tube plugging criteria. As shown in Figure 81 this leakage limit provides for detection of 0.41 inch cracks at nominal leak rates and 0.62 inch cracks at the -95% confidence level leak rates. Thus, the 150 gpd limit provides for plant shutdown prior to reaching critical crack lengths for SLB conditions at leak rates less than a -95% confidence level and for 3 times normal operating pressure differentials at less than nominal leak rates. The tube plugging limits coupled with 100% inspection at affected TSP locations provide the principal protection against tube rupture. Consistent with a defense in-&pth approach, the 150 gpd leakage limit provides further protection against tube rupture. In addition the 150 ' gpd limit provides the capability for detecting a crack that might grow at greater than expected rates and thus provides additional margin against exceeding SLB leakage limits. 8.4 Example SLB Analyses As discussed in Section 6, the EPRI database and the EPRI SLB leak rate and burst correlations are recommended for application to the Beaver Valley-1 IPC. Example SLB analyses are provided in this section applying the EPRI database and correlations. For comparison, SLB leak rates are also calculated using the NRC database (See Section 6) and the draft NUREG-1477 methodology. SLB leak rates are provided for the reference log logistic POL correlation and, for information, leak rates for the additional five POL correlations discussed in Section 6 are also provided. Calculations are performed for Cycle 10 assuming either a 1.0 or 2.0 volt IPC had been implemented for this cycle as a reasonable estimate of Cycle 11 performance following application of a voltage based IPC repair limit. 8-4
l
~
To A..e the impact of applying the 1.0 or 2.0 volt repair limit versus the standard 40% depth limit actually applied for Cycle 10, SLB leak rate and burst probability analyses are also performed for the actual distributions left in service for Cycle 10. It is shown by these , analyses that either the 2.0 or 1.0 volt IPC result in only small increases in potential leakage i and burst probability compared to a 40% depth repair limit. BOC voltage distributions were developed in Section 7.4 for both an assumed 1.0 or 2.0 volt IPC and the actual distribution based on a 40% depth repair limit. For each repair limit, BOC distributions were developed for the draft NUREG-1477 POD = 0.6, for POD = 1.0 and for the attemate new indication method described in Section 7.4. Based on evaluations of projections versus actual distributions for other plants following IPC implementation, the new indication method has provided the best comparison between projections and actual distributions for RPC confirmed indications. Monte Carlo analyses were performed to project EOC voltage distributions for each BOC distribution developed in Section 7.4. Figure 8-2 shows the BOC and projected EOC voltage distributions for the assumed IPC of 2.0 volts for each of the three BOC distributions. Le maximum projected EOC voltages are 3.8,4.2 and 4.4 volts for the new indication method, POD = 1.0 and POD = 0.6, respectively. The corresponding number ofindications are 381, 558 and 939. The new indication method yields a lower maximum EOC voltage than the other methode N this distribution, as the 3.6 volt bobbin indication left in service with an indicatd dept M was assumed to be RPC NDDTor application of the methodology and weigh'..:d to oba 0.3 indication left in service. The 3.6 volt indication was not RPC inspected, as the . n was not distorted and had a depth call by the bobbin coil inspection. The n:. acation method projects the potential RPC confirmed indications, while the POD = 0.6 method provides a very conservative estimate of the total number of bobbin indications. For each of the three EOC distributions, the estimated SLB leak rate was calculated by applying the log logistic POL correlation with the EPRI leak rate versus voltage correlation and the draft NUREG-1477 leak rate meth.odology. The SLB leak rate and burst probability analyses of this report utilize a deterministic analysis applied to the EOC voltage distributions such as Figure 8-2. Results of the analyses are given in Table 8-1. The EPRI leak rate correlation applied to the conservative POD = 0.6 distribution is the recommended methodology for the Beaver Valley-1 IPC, unless an alternate method is accepted by the NRC prior to the IPC implementation. The projected EOC SLB leak rate for the recommended
. EPRI methodology with a POD of 0.6 is 0.044 gpm, while the draft NUREG-1477 method yields a very conservative 0.46 gpm for the same distribution. Both the recommended EPRI correlation method and the draft NUREG method yield a leak rate much lower than the allowable SLB leak rate of 6.6 gpm. He projected EOC SLB tube burst probability of 6.3x10" is also significantly less than the 2.5x10 2 acceptance guideline. Thus,it can be reasonably expected that implementation of a 1.0 or 2.0 volt IPC repair limit for Cycle 11 will result in a SLB leak rate and a tube burst probability less than the allowable limits.
The new indication methodology for defining the BOC distribution results in SLB leak rates about a factor of two lower than the POD of 0.6 method and about 25% lower than the POD of 1.0 method. For this application, the POD of 1.0 yields higher leakage estimates than the new indication method due to the large number of RPL NDD indications left in service. The 8-5 i 1
POD methods assume that all the RPC NDD indications can result in leakage, while the new indication method assumes only 30% of the NDD indications will become confirmed and potentially contribute to leakage. Figure 8-3 shows the BOC and projected EOC voltage distributions for the actual indications left in service. The maximum EOC volts, SLB leak rates and burst probabilities are given in Table 8-1 and can be compared with the results for an assumed IPC of 2.0 volts. It is seen that the estimated SLB leak rates and burst probabilities for application of the 40% depth repair limits with a POD of 0.6 are only about 15% and 25%, respectively, lower than obtained for an IPC of 2.0 volts. In part, this results from the large number of RPC NDD indications left in service. However, the new indication method which weights the number of l RPC indications left in service by a 0.3 factor results in only 30% lower SLB leak rates for the 40% depth repair limit than for the 2.0 volt IPC. This result demonstrates the ) conservatism of applying a 1.0 or 2.0 volt IPC for Beaver Valley-l. j H SLB analyses were also performed for an assumed IPC of 1.0 volt at BOC-10. The resulting voltage distributions are shown in Figure 8-4 and the leak and burst results are also summarized in Table 8-1. It is seen that the resulting SLB leak rates for a 1.0 volt IPC are approximately 5% lower than that for a 2.0 volt IPC and burst probabilities are about 15% lower. SLB sensitivity analyses were performed to assess the influence of the alternate POL correlations on leakage and the differences between the EPRI and NRC databases on leakage and burst probability. Results of these analyses are given in Table 8-2 for the POD = 0.6 BOC distribution recommended by draft NUREG-1477. The differences between the log logistic and log normal, which are considered to be acceptable POL correlations, are negligible. When the assumption of a constant leak rate per indication independent of voltage is applied per the draft NUREG-1477 methodology, the influence of the attemate POL correlations on the leak rate is calculated to be more significant than for the EPRI leak rate correlation. The largest differences from the reference log logistic POL form are found for the Cauchy POL forms, which include an unrealistically high probability ofleakage at low voltages (< 2 volts), and would be expected to result in higher leak rates. The differences between log logistic and Cauchy POLS are smaller for the EPRI leak rate versus voltage correlation than for the draft NUREG-1477 method since the voltage correlation results in much lower leak rates in the low voltage region. The Cauchy POL distributions are considered to be unrealistic as they result in about a 3% probability of leakage at zero volts and no undetected (field NDD call) pulled tube indication has been found to have crack depths greater than about 65% and thus would not leak at accident conditions. Similarly, the linear logistic and linear normal POL forms result in non-zero POL at zero volts and are not considered to be acceptable POL forms. In summary, the log logistic and log normal distributions reasonably represent the data and both yield comparable leak rates. Thus the EPRI recommended log logistic POL is an acceptable representation of the data and continued analyses for all six POL forms is not warranted. 8-6
These leak rate analyses utilize a deterministic method (Reference 9) which includes an estimated covariance term when applied to the EPRI leak rate versus voltage correlation. Prior analyses of the sensitivity ofleakage to the POL form, as performed for Farley-1 and D. C. Cook-1, did not include this covariance term and showed less dependence of leakage on the POL form for the EPRI correlation than shown in Table 8-2. The covariance term increases the leakage for the log Cauchy and linear forms for the POL. To assess the deterministic method for Beaver Valley-1, full Monte Carlo leak rate analyses were performed for the EPRI database and an assumed 2.0 volt IPC with a POD = 0.6. The Monte Carlo results versus the deterministic method were found to be: 0.063 versus 0.044 for the log logistic POL,0.052 versus 0.041 for the log normal POL,0.33 versus 0.10 for the log Cauchy l POL, 0.12 versus 0.082 for the linear logistic POL,0.10 versus 0.066 for the linear normal ' POL and 0.32 versus 0.15 for the linear Cauchy POL. These differences of up to about 0.2 gpm between the deterministic and Monte Carlo methods are similar to that found for another plant at higher leak rate levels. The relative dependence of the leak rate on the form of the POL is nearly the same between the deterministic and Monte Carlo methods. 'Ihe Monte Carlo shows the biggest difference from the deterministic method for the Cauchy POL forms which can be reasonably expected as the Cauchy POLS have longer tails on the correlation. These results support the use of either the deterministic or Monte Carlo methods for Beaver Valley-1 analyses However,if the deterministic methods result in leak rates within a few tenths of a gpm of the allowable limits, a Monte Carlo leak rate analysis would be appropriate. Based on the low leak rates found from the Cycle 10 analyses, it is expected that the Beaver Valley-1 SLB leak rates will be well below the allowable limit and the deterministic methods for application of the EPR.I leak rate correlation would be acceptable. If leak rate analyses are only required for the log logistic POL correlation, full Monte Carlo analyses would be applied. It is seen from Table 8-2 that the EPRI and NRC databases lead to essentially the same leak rates for the draft NUREG 1477 methodology with the EPRI database yielding negligibly higher leak rates as expected from the data averages and standard deviations given in Table 6-5. The predicted tube burst probabilities are significantly higher for the NRC database than for the EPRI database. This results as the NRC database includes test results having very high burst pressures for the voltage level of the indications. The inclusion of these conservative burst test results in the correlation significantly increases the standard deviation of the regression correlation which then results in higher ~ probabilities of low burst pressures at a given voltage level. The EPRI outlier evaluation of Reference 3 recommends exclusion of these data from the correlations and is the reccmmended database for the Beaver Valley-1 IPC. It is concluded from the above analyses that implementation of a 1.0 or 2.0 volt IPC repair limit for Cycle 11 at Beaver Valley-1 can be expected to result in SLB leak rates and tube burst probabilities within allowable limits. The use of the EPRI database and POL / leak rate correlations results in substantial SLB leak and burst margins. The use of the the attemate POL l forms and the NRC database also result in margins against allowable limits although the burst probability is unrealistically high for the NRC database independent of a 2.0 volt,1.0 volt or 40% depth repair limit. In addition, the results show small differences in projected SLB leak rates between application of 40% depth and 1.0 or 2.0 volt repair limits. 8-7
Table 8-1 Frample SLB Analysis Results (EPRI Database) for Pmjected EOC-10 Distributions BOC Number Maximum SLB Imk Rate-gpm SLB Distribution of EOC Burst Method Indications Volts Draft EPRI Probabluty I NUREG Corr. l Assumed IPC = 2.0 Volt for Cycle 10 POD = 0.6 939 4.4 0.46 0.044 6.3 E-04 POD = 1.0 558 4.2 0.32 0.029 3.4 E-04 New Ind. Method 381 3.8 '0.24 0.021 2.2 E-04 Assumed IPC = 1.0 Volt for Cycle 10 POD = 0.6 898 4.4 0.43 0.041 5.5 E-04 POD = 1.0 517 4.2 0.28 0.026 2.7 E-04 New Ind. Method 340 3.8 'O.19 0.017 1.5 E-04 i Actual BOC-10 Indications for 40% Depth Repair Limit POD = 0.6 747 4.4 0.38 0.038 4.7 E-04 POD = 1.0 366 4.1 0.22 0.021 1.8 E-04 New Ind. Method 216 3.7 0.15 0.013 9.1 E-05 1 8-8
Table 802 Sensitivity of SLB Analyses to EPRI versus NRC Database and Correlation EPRI Database NRC Database Leak Rate spm Bmt Leak Rate-gpm Burs Ds Co ation Method Draft LeakNolt Draft NUREG Assumed IPC = 2.0 Volts ibr Cycle 10 POD = 0.6 log logistic 0.46 0.044 6.3 E-04 0.44 1.4 E-02 log normal 0.35 0.041 0.33 log Cauchy 2.26 0.10 2.13 linear logistic 1.59 0.082 1.51 linear normal 1.22 0.066 1.16 linear Cauchy 3.57 0.15 3.36 POD = 1.0 log logistic 0.32 0.029 3.4 E-04 0.31 7.9 E-03 New Ind. Method log logistic 0.24 0 021 2.2 E-04 0.23 5.2 E-03 Assumed IPC = 1.0 Volt for Cycle 10 , POD = 0.6 log logistic 0.43 0.041 5.5 E-04 0.41 1.23 E-02 log normal 0.32 0.039 0.31 log Cauchy 2.16 0.096 2.04 linear logistic 1.52 0.077 1.44 linear normal 1.16 0.062 1.10 linear Cauchy 3.43 0.14 3.23 POD = 1.0 log logistic 0.28 0.026 2.7 E-04 0.26 6.3 E-03 New Ind. Method log logistic 0.19 0.017 1.5 E-04 0.18 3.6 E-03 Actual BOC-10 Indications L4ft in Service POD = 0.6 log logistic 0.38 0.038 4.7 E-04 0.36 1.0 E-02 log normal 0.29 0.036 0.28 log Cauchy 1.87 0.084 1.77 linear logistic 1.33 0.067 1.26 Imear normal 1.01 0.055 0.97 linear Cauchy 2.96 0.12 2.79 POD = 1.0 log logistic 0.22 0.021 1.8 E-04 0.21 4.3 E-03 New Ind. Method log logistic 0.15 0.013 9.1 E-05 0.14 2.2 E-03
- 7 _ , . , . _ . _ _ - , - - _ __
i 4 1 Beaver Valley 1 , Leak Rate vs. Axial Crack Length i 10 -
- MEAN 1 r
@ ! 0.10 GPM 95% PRED'N INPL % 0.1 C5- r- ------ ---- ---------------------- ---- :.
5 s
- 0.01 r . :
$ 5 ! -
1 0.001 [- -
.3 -
i ! , 0.0001 r 0.41" i j 0.62" E ! ! 0.00001 O.1 1 i Axial Crack Length (inches) i Figure 8-1. Normal Operation Leak Rate vs. Axial Crack Length
Figure 8-2. Example BOC and EOC Voltage Distributi:ns f:r an Assumed IPC l of 2.0 Volts ! l l 60 NewIndication Method l h 40 _ i E j 20 0
. r 111rui..._.._ 14 26 18 3 32 34 38 88 4 AJ 44 1
0.2 04 04 Os 1 1.2 14 16 18 2 2.2 Volts POD = 1.0 80 E Ji! o ao _ _ _ Y
, . rl((lttu . . . ._ _ . - _
to to 18 2 2.2 14 2S 18 3 12 14 38 18 4 4.2 4.4 02 04 OS 08 1 1.2 Volts 150 PCD = 0.6 i E - g goo _ _ _ a s , O ) 50 - - o' - - Z o
.2 .. .. .. , ,,
r ((ltirui . . ._ _ - ,_
,.,,,.2 12 .. 2.
.2 ..
Volts l I BOCINDICATIONS M EOCINDICATIONS 8 -11
Figure 8.3 Example BOC and EOC Voltage Distributions for ActualIndications Left in Service 40 NewIndication Method
, 30 -
c 8
.0 l
~-
] 20 -
l o 10 - - - -
)
o
. f r lcl.Irl .. .. . _ _
.. .. .. .. , ,, .. ,. ,. . 1.
Volts
.. 1. .. . .. .. 1. .. .~ ..
POD = 1.0 a y 40 - - - E
~
N 0
' ' ,3 ,5 m - _ - _ . ~ . ,, ..
0.2 04 DS 68 1 1.2 to 16 14 2 12 to 18 18 3 32 3.4 to 14 4 42 44 Volts 120 POD = 0.6 100 - 80 - - -
.a ? 60 - - -
5 cr 40 - - - Z 20 -- - - - 0 ' - I" ' ""-~~-~-' - - '~ -- - l 0.2 9. 60 08 1 12 14 10 18 2 2.2 14 28 18 3 32 34 36 38 4 4.2 44 l Volts l I BOCINDICATIONS M EOCINDICATIONS 8 - 12
Figure 8-4 Example BOC and EOC Voltage Distributions for an Assumed IPC of 1.0 Volt 60 New Indication Method
-gE 40 8
e S O j 20
. r .R n . . - - . - - . - . - ._
0 02 04 08 08 1 12 44 t8 1.8 2 12 24 18 26 3 32 34 36 38 4 42 44 Volts POD = 1.0 . 80 8 j _ _ _ i i o 40 - N . O
" ( 'EI'~"- - ^ ^ - -^ - ^^ -
0.2 04 08 08 1 12 14 10 1.8 2 2.2 14 28 14 3 3.2 34 36 38 4 4.2 44 Volts 150 POD = d.6 m ' j 100 - - - A E_ o' 50 - - - - Z 0
. r [e I!rI,5J - - _ . - _ . _ - __ ..- .
02 84 08 04 1 1.2 to 16 18 2 2.2 14 28 18 3 32 34 as 38 4 42 44 Volts l l BOCINDICATIONS M EOCINDICATIONS 8 - 13
\
4 b u i
9.0 REFERENCES
(1) Report TR-100407, Revision 1, "PWR Steam Generator Tube Repair Limits - Technical Support Document for Outside Diameter Stress Corrosion Crack at Tube l Support Plates," Electric Power Research Institute, Draft Report, August 1993. (2) Report NP-7480-1, Volume 1, Revision 1, " Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates - Database for Altemate Repair Limits, Volume 1: 7/8 Inch Diameter Tubing," Electric Power Research Institute, December,1993. (3) EPRI Letter, " Exclusion of Data from Altemate Repair Criteria (ARC) Databases Associated with 7/8, inch Tubing Exhibiting ODSCC," D. A. Steininger (EPRI) to J. Strosnider (USNRC), April 22,1994 [to become Appendix E of Reference (2)). (4) WCAP-13579, "Be.'ver Valley Unit 1 Steam Generator Tube Plugging Criteria for Indications at Tube Support Plates", March,1993, (Westinghouse Proprietary Class 2). (5) WCAP-12871, Revision 2, "J. M. Farley Units 1 and 2 SG Tube Plugging Criteria for ODSCC at Tube Support Plates", February 1992, (Westinghouse Proprietary Class 2). (6) NUREG-1477 (draft), " Voltage-Based Interim Plugging Criteria for Steam Genera-tor Tubes - Task Group Report," United States Nuclear Regulatory Commission, June 1,1993. (7) (United States Nuclear Regulatory Commission) Meeting with EPRI, NUMARC,
" Resolution of Public Comments on Draft NUREG-1477," United States Nuclear Regulatory Commission, February 8,1994.
(8) Regulatory Guide 1.121 (drafi), " Bases for Plugging Degraded PWR Steam Generator Tubes," United States Nuclear Regulatory Commission, issued for comment in August,1976. (9) WCAP-14046, "Braidwood Unit 1 Technical Support for Cycle 5 Steam Generator Interim Plugging Criteria," May 1994 (Westinghouse Proprietary Class 2). l l 1 l l l 9-1 l l
APPENDIX A NDE DATA ACQUISITION AND ANALYSIS GUIDELINES A.1 INTRODUCTION This appendix contains guidelines which provide direction in applying the ODSCC attemate repair criteria described in this report. The procedures for eddy current testing using bobbin coil and rotating pancake coil (RPC) techniques are summarized. The procedures given apply to the bobbin coil inspection, except as explicitly noted for RPC inspection. The methods and techniques detailed in this appendix are requisite for the Beaver Valley Unit 1 implementation of the alternate repair criteria and are to be incorporated in the applicable inspection and analysis procedures. The following sections define specific acquisition and analysis . parameters and methods to be used for the inspection of the steam generator tubing. A.2 DATA ACQUISITION The Beaver Valley Unit I steam generators utilize 7/8" OD x 0.050" wall, Alloy 600 mill-annealed tubing. The carbon steel support plates are designed with drilled holes. A.2.1 Probes Bobbin CatLProbes 1 Eddy current equipment used shall be the ERDAU (Echoram Tester), Zetec MIZ-18 or other equipment with similar specifications. To maximize consistency with laboratory data, differential bobbin probes with the following parameters shall be used: . The bobbin probe diameter shall be optimized to provide the largest practical fill factor for the tubes inspected: Nominal Tube ID: 0.775" Primary Probe Size: 0.720" Probe Sizes: 0.640" - 0.740" Fill Factor: 68 % - 91 % i A-1 l
The primary probe sin should be used whenever the tube can be inspiected with the 0.720" diameter probe. Alternate probe sizes can be used when specific tubes cannot be fully , inspected with the 0.720" probe, such as tubes with sleeves at TSP intersections and small radius tubes sleeved in the tubesheet region. (At this time there are no sleeves installed in the u Beaver Valley-1 steam generators.) Probe diameters ranging from 0.680" to 0.740" have been i shown to produce good agreement with the nominal 0.720" probe size, which was used to compile the EPRI ARC database; see Figure A-1. For all probe diameters, the centering devices must provide stable positioning within the nominal tube I.D. to minimize the variability of the probe response as measured with the four hole wear standard. Alternate probes must have voltage normalization at the 20% ASME holes in the same manner as the nominal 0.720" probe and must meet the acceptance criteria utilizing the probe wear standard (see Sections A.2.2 to A.2.5). i The use of smaller probes is contingent upon performance demonstration of the smaller probe in blind testing which uses the primary probe (0.720") diameter data as ground truth data. In i the absence of such performance demonstration data, it is recommended that rotating pancake probes (or other qualified techniques) be used to inspect support plates that cannot be accessed with the bobbin probes within the 0.640" to 0.740" diameter range. Each probe shall employ two bobbin coils, each 60 mils long with 60 mils between the coils , (center to center spacing equal to 120 mils). Either magnetically biased or non-biased coils l may be employed. Table A-1 presents the behavior of 0.720" bobbin probes for an ASME ! standard, a tube support plate simulation, the 4 hole wear standard and an EDM (electron i discharge machined) notch standard for both coil configurations. There is no significant i difference in the amplitudes of the responses from non-biased or magnetically biased probes ! for any of the discontinuities tested. Similar results were reported on pulled tube specimens , from Plant R as showr. as Table A-2. l Rotatine Pancake Coil Probes L The pancake coil diameter shall be s 0.125". While any number coil (i.e.,1,2 or 3-coil) l probe can be utilized, it is recommended that if a 3-coil probe is used, any voltage l measurements should be made with the probe's pancake coil rather than its circumferential or . i axial coil. The maximum probe pulling speed shall be =0.2 inisec for the 1-coil or 3-coil probe, or 0.4 inisec for the 2-coil probe. The maximum rotation speed shall be a300 rpm; this would result in a pitch of =40 mils for the 3 coil' probe. I A-2
I i 1 A.2.2 Calibration Standards i Bobbin coils.tandards To provide IPC implementation at Beaver Valley Unit I consistent with the development and analyses of the supporting database report and with prior NRC-approved IPC applications, a ~ probe wear standard (to guide probe replacement) and AShE standards calibrated against the reference laboratory standard are to be utilized. The bobbin coil calibration standard shall contain: i
- Four 0.033" diameter through wall holes,90* apart in a single plane around the l tube circumference. The hole diameter tolerance shall be 0.001"
. One 0.109" diameter flat bottom hole,60% through from OD.
. One 0.187" diameter flat bottom hole,40% through from the OD.
l l
= Four 0.187" diameter flat bottom holes,20% through from the OD, spaced 90*
apart in a single plane around the tube circumference. The tolerance on hole diameter and depth shall be *0.001"
- A simulated support ring,0.75" thick, comprised of SA-285 Grade C carbon steel or equivalent with a hole diameter of 0.890" - 0.895".
. A probe wear standard shall be employed for monitoring the degradation of probe centering devices leading to off-center coil positioning and potential variations in flaw amplitude responses. This standard shall include four through wall holes, 0.067" in diameter, spaced 90* apart around the tube circumference with an axial spacing such that signals can be clearly distinguished from one another (see Section A.2.3).
This calibration standard will have been calibrated against the reference standard used for the APC laboratory work. Voltages reported for IPC/APC applications shall include the cross calibration differences between the field and laboratory standard. A-3
1 REC. Standard The RPC standard shall contain; s
- Two axial EDM notches, located in-line (at the same circumferential orientation) i i
but spaced axially on centers 1.0" apart, each 0.006" wide and 0.5" long, one 80% i and one 100% through wall from the OD. i e Two axial EDM notches, located at the same axial position but 180' apart ; circumferentially, each 0.006" wide and 0.5" long, one 60% and one 40% through well from the OD.
- Two circumferential EDM notches, one 50% throughwall from the OD with a 75' (0.57") are length, and one 100% throughwall with a 26' (0.20") are length, with both notches 0.006" wide.
, t
- A 100% throughwall hole,0.067" in diameter.
- A simulated support segment,270* in circumferential extent,0.75" thick, i comprised of SA-285 Grade C carbon steel or equivalent with hole diameter of l 0.890" - 0.895". I The center to center distance between the support plate simulation and the nearest slot shall :
be at least 1.25". The EDM slots may be positioned azimuthally such that the overall length of the standard may be minimized. The center to center distance between the EDM notches i shall be at least 1.0". The tolerance for the widths and depths of the notches shall be . 0.001". The tolerance for the slot lengths shall be *0.010". l 1 l A.2.3 Application of Bobbin Coil Probe Wear Standard f A calibration standard has been designed to monitor bobbin coil probe wear (see Figure A-2). ;
- During steam generator examination, the bobbin coil probe is inserted into the wear l l monitoring standard; the initial (new probe) amplitude response on the 400/100 kHz mix '
channel from each of the four holes is deternised and compared on an individual basis with j l- subsequent measurements. Signal amplitudes or voltages from the individual holes must , remain within 15% of their initial amplitudes for an acceptable probe wear condition. If this I condition is not satisfied for all four holes, then the probe must be replaced, and all tubes A-4 ) b
.--4, .,*ermm ---- t -- - , - --e-w-*- ---- - - + ---- -- .--,, - - - - - - - - -- -
tested with that probe since the last acceptable probe wear check must be re-examined with a new probe. A.2.3.1 Placement of Wear Standards Under ideal circumstances, the incorporation of a wear standard in line with the conduit and guide tube configuration would provide continuous monitoring of the behavior of bobbin f probe wear. However, the curvature of the channelhead places restrictions on the length of in line tubing inserts which can be accommodated. The spacing of the ASME Section XI l holes and the wear standard results in a length of tubing which cannot be freely positioned l within the restricted space available. The flexible conduit sections inside the channelhead, together with the guide tube, limit the space available for additional in line components. Voltage responses for the wear standard are sensitive to bending of the leads, and mock up tests have shown sensitivity to the robot end effector position in the tubesheet, even when the wear standard is placed on the bottom of the channelhead. Effects such as bending of the probe leads can result in premature probe replacement. Wear standard measurements must permit some optimization of positions for the measurement and this should be a periodic measurement for inspection efficiency. The pre-existing requirement to check calibration j using the ASME tubing standard is satisfied by periodic probing at the beginning and end of each probe's use as well as at four hour intervals. The wear standard holes' responses may be the calculated average of multiple scans to provide an improved statistical basis for the periodic measurements. This frequency is adequate for wear standard purposes as well. Evaluating the probe wear under uncontrollable circumstances would present variability in response due to channelhead orientations rather than changes in the probe itself. A.2.4 Acquisition Parameters
'Ihe following parameters apply to bobbin coil data acquisition and should be incorporated in the applicable inspection procedures to supplement (not necessarily replace) the parameters normally used.
Test Freauencies j This technique requires the use of 400 kHz and 100 k'Hz test frequencies in the differential ) mode. It is recommended that the absolute mode also be used, at test frequencies of 100 kHz l and 10 kHz. The low frequency (10 kHz) channel should be recorded to provide a positive means of verifying tube support plate edge detection for flaw location purposes. The A-5
4 1 1 400 kHz channel or the 400/100 kHz mix are also used to assess changes in signal amplitudes for the probe wear standard as well as for flaw detection. RPC frequencies should include 400 kHz,300 kHz and to kHz. Digitizinn Batt A minimum bobbin coil digitizing rate of 30 samples per inch shall be used. Combinations of probe speeds and instrument sample rates should be chosen such that: Sample Rate (sample $sec.) 130 (samplegin.) Probe Speed (In.jsec.) A.2.5 Analysis Parameters This section discusses the methodology for establishing bobbin coil data analysis variables such as spans, rotations, mixes, voltage scales, and calibration curves. Although indicated depth rueasurement may not be required to support an alternative repair limit, the methodology for establishing the calibration curves is presented. The use of these curves is recommended for consistency in reporting and to provide compatibility of results with subsequent inspections of the same steam generator and for comparison with other steam generators and/or plants. Spani Spans and rotations can be set at the discretion of the user and/or in accordance with applicable procedures, but all TSP intersections must be viewed at a span setting which provides 3/4 full screen amplitude for a 2.0 volt peak,to peak signal with IPC-calibrated bobbin probes; the corresponding span for RPC probes should permit viewing of small amplitude RPC indications, i.e., a 2.0 volt peak to peak signal should give at least 3/4 full screen amplitude when a 0.5" throughwall EDM notch reads 20 volts. Rotation The signal from the 100% through wall hole at 400 kHz should be set to 40' ( l'), with the initial signal excursica down and to the right during probe withdrawal. The signal from the probe motion for the 400/100 kHz differential mix should be set to horizontal, with the initial A-6
1 excursion of the 100% through wall hole signal going down and to the right during probe withdrawal. 1 Voltane SG12
- 1) Bobbin - The peak-to-peak signal amplitude of the signal from the four 20% OD flaws should be set to produce a field voltage equivalent to that obtained for the EPRI lab standard. The EPRI laboratory standard normalization voltages are 4.0 volts at 400 kHz for 20% ASME holes and 2.75 volts at 400/100 kHz mix for 20% ASME holes.
The field standard will be calibrated against the laboratory standard using a reference laboratory probe to establish voltages for the field standard that are equivalent to the above laboratory standard. These equivalent voltages are then set on the field standard to establish the calibration voltages. Voltage normalization for the specific standard in the 400/100 mix is recommended to minimize analyst variability in establishing the mix.
- 2) RPC - The RPC amplitude shall be set to 20 volts for the 0.5 inch throughwall notch at 400 kHz and 300 kHz; i.e., the amplitude shall be set to 20 volts for each channel.
Mixes A bobbin coil differential mix is established with 400 kHz as the primary frequency and 100 kHz as the secondary frequency, and suppression of the tube support plate simulation should be performed. Complementary information may be obtained from a 200 kHz/100 kHz mix; e.g., influence of dents at TSP's can be inferred from the difference with the 400 kHz/100 kHz mix. Calibration.Cyng For the 400 kHz differential channel, establish a curve using measured signal phase angles in combination with the "as-built" flaw depths for the 100%,60%, and 20% flaws on the calibration standard. For the 400/100 kHz differential mix channel, establish a curve using measured signal phase angles in combination with the "as-built" flaw depths for the 100%, 60%, and 20% flaws on the calibration standard. A-7
A.2.6 Analysis Methodology Bobbin coil indications attributable to ODSCC at support plates are quantified using the Mix 1 (400 kHz/100 kHz) data channel. This is illustrated with the example shown in Figure A-3. The 400/100 kHz mix channel and other channels appropriate for flaw detection (400 kHz,200 kHz) can be used to locate the indication of interest within the support plate signal. The largest amplitude portion of the lissajous signal representing the flaw should be measured using the 400/100 kHz Mix 1 channel to establish the peak to-peak voltage as shown in Figure A-4. Initial placement of the dots for identification of the flaw may be performed from the raw frequencies as shown in Figures A-3 to A-5, but the final peak-to-peak measurements must be performed on the Mix 1 lissajous signal to include the full flaw l segment of the signal. It may be necessary to iterate the position of the dots between the identifying frequency data (e.g.,400 kHz) and the Mix 1 data to assure proper placement of the dots. As can be seen in Figures A-4 and A-5, failure to do so can significantly change the amplitude measurement of Mix 1 due to the interference of the support plate signal in the raw frequencies. The voltage measured from Mix 1 is then entered as the analysis of record ) for comparison with the repair limit voltage. l To support the uncertainty allowances maintained for the plugging criterion, the difference in amplitude measurements between independent analysts for each indication will be limited to 20%. If the voltage values called by the independent analysts deviate by more than 20% and one or both of the calls exceeds the voltage repair criterion, resolution by the lead analyst will be performed. This resolution process results in enhanced confidence that the reported voltage departs from the correct call by no more than 20%. A.2.7 Reporting Guidelines - The reporting requirements identified below are in addition to any other reporting requirements specified by the user. MinimunLBiguirements At a minimum, flaw signals in the 400/100 mix channel at the tube support plate intersections must be reported. Flaw signals, however small, should be reported for historical purposes and to provide an assessment of the overall condition of the steam generator (s). A-8 l l l
l i
.l 1
Additional Requirements ; For each reported indication, the following information should be recorded: l l Tube identification . (row, column) Signal amplitude (volts) Signal phase angle (degrees) -{ Indicated depth (%)t Test channel (ch#) Axial position in tube (location) f Extent of test (exter l RPC reporting requirements should include a minimum of: type of degradation (axial, l circumferential or other), maximum voltage, phase angle, crack lengths, and location of the crack within the TSP. The crack axial center may not coincide with the position of maximum t emplitude. For IPC applications, locations which do not exhibit flaw-like indications in the l RPC isometric plots may continue in service, except that all intersections exhibiting flaw-like : bobbin behavior and bobbin amplitudes in excess of an upper voltage limit typical of the full
-l APC repair limit (defined by approved IPC criteria) must be repaired, notwithstanding the !
RPC analyses. , ; i RPC isometrics should be interpreted by the analyst to characterize the signals observed; only l featureless isometrics are to be reported as NDD. Signals not interpreted as flaws include dents, lift off, deposits, copper, magnetite, etc.; these represent "non-relevant" conditions l which do not impact tube integrity as reported. , A.3 DATA EVALUATION l A.3.1 Use of 400/100 Differential Mix for Extracting the Bobbin Flaw Signal i In order to identify a discontinuity in the composite signal as an indication of a flaw in the l tube wall, a simple signal processing algorithm for mixing the data from the two test 1 9 It is recommended that an indicated depth be reported as much as possible rather than some letter code. While this measurement is not required to meet the altemate repair limit, this information might be required at a later date and/or otherwise be used to develop enhanced analysis techniques. A-9
)
l
frequencies is used to reduce the interference from the support plate signal by about an order of magnitude. The test frequencies suggested for this signal processing are 400 kHz and 100 kHz for 50 mil wall Inconel 600 tubing. The processed data is referred to as 400/100 mix channel data. This procedure may also reduce the interference from magnetite accumulated in the crevices. Any of the differential data channels including the i mix channel may be used for flaw detection (though the 100 kHz channel is subject to influence from many different effects), but the final evaluation of the signal detection, amplitude and phase will be made from the 400/100 differential mix channel. Upon detection of a flaw signal in the differential mix channels, confirmation from other raw channels is not required. The voltage scale for the 400/100 differential channel should be normalized as described in Section A.2.5. With a typical bobbin calibration (Figure A-6), flaw signals reside in the upper half of the impedance plane (O' to 180'). For phase angles from 0* to the angle corresponding to the 100% hole - typically around 35' in the 400/100 kHz mix, the flaw is assumed to have I.D. origin; phase angles from 35' to 180' are attributed to O.D. origin. Industry practice provides 10' variation about O' or 180' due to redundancy of shallow flaws and probe wobble or geometry change, i.e., lift off signals. Thus, flaw signals are expected to be observed in the 10' - 170* range. Examination of the calibration curve shows that the 0% depth intercept occurs at phase angles below 170*, usually in the 125' - 150* range. Since ODSCC depth is not well represented by the phase angle measurement, especially for small amplitude signals, some flaw-like signals may exhibit phase angles at or beyond the 0% intercept but less than or equal to 170' (Figures A-7 and A-8). Industry practice regards these signals as non-l reportable, and RPC testing of these signals at plants such as Plant D-1 and Plant A-2 has not confirmed the presence of detectable cracks. Nevertheless, inasmuch as these signals may ! represent ODSCC, they should be reported as O.D. indications of unmeasurable depth. l l In some cases it has been observed (Figure A-9) that I.D. oriented flaw signals, those with l phase angles :t 10* but s 35' (100% hole phase angle in the 400/100 mix), are encountered in non-dented support plate intersections. It has been confirmed at Plant A-2 and at Plant L from tube pull information or from RPC testing (Figu're A-10) that these apparent I.D. origin l bobbin signals correlate well with ODSCC. To assure appropriate disposition of these signals within the attemate repair framework, these signals will be reported in the same fashion as l those which present clear O.D. phase information. For purposes related to IPC disposition I criteria, all potential ODSCC may be classified as possible indications (PIs). A - 10 l .
The Beaver Valley Unit I reporting guidelines require that TSP flaw signals with I.D. criented phase angles be reported as PIs, as is done for the measurable O.D. oriented indications. For the unmeasurable O.D. signals (phase angle 2 0% intercept), the designation applied is UOA (unusual O.D. phase angle). All PIs > the voltage threshold for RPC inspection,1.5 volts, will be subject to RPC testing. Indications continued in service in p:.or years because of acceptable voltage or RPC NDD results may upon re-inspection in subsequent outages be evaluated as not exhibiting flaw characteristics. Rese signals will be designated INR (indication not reportable) but the location, phase angle, and amplitude will be recorded to facilitate year to year comparisons and growth rate determinations. This evaluation procedure requires that there is no minimum voltage for flaw detection purposes and that all recognizable flaw signals, however small, be identified. The intersections with flaw signals greater than 1.5 volts will be inspected with RPC in order to confirm the presence of ODSCC. Although the bobbin signal voltage is not a measure of the flaw depth, it is an indicator of the tube burst pressure when the flaw is identified as axial ODSCC with or without minor IGA. UOA and INR signals will be included in the RPC sampling plan, with emphasis on sample RPC inspection of indications greater than the voltage repair limit. This procedure using the 400/100 mix for reducing the influence of support plate and magnetite does not totally eliminate the interference from copper, alloy property change or dents. These are discussed below. A.3.2 Amplitude Variability Figures A-11 and A-12 illustrate how significant amplitude differences between two analysts measurements might arise: Analyst 1 (Figure A-11) has made a more conservative estimate by placing his measurement dots where the differential phase in all channels trends out of the flaw plane, while flaw plane phase angles appear beyond the upper dot placement in Analyst 2's graphic (see Figure A-12). Analyst l's conservative call produces a peak-to-peak voltage (1.72V) one third (1/3) greater than Analyst 2's result. Figure A-12 represents an' example in ; which the placement of the max rate dots which establish the maximum estimated flaw. depth under-estimates the apparent flaw-related peak-to-peak voltage. He correct placement (Figure A-12) also corresponds to the maximum volta'ge measurement on the 400 kHz raw frequency data channel. A - 11
1 l In some cases, it' will be found that little if any dermitive help is available from the use of the raw frequencies. Such examples are shown in Figures A-13 and A-14. Consequently, the placement of the measurement dots must be made completely on the basis of the Mix 1 channel lissajous figure as shown in the lower right of the graphic. An even more difficult example is shown in Figure A-15. 'Ihe logic behind the placement of the dots on Mix 1 is that sharp transitions in the residual support plate signals can be observed at the locations of both dots. This is a conservative approach and sho~uld be taken whenever a degree of doubt as to the dot placement exists. The source of error becomes more noticeable when the data involves complicating factors or interferences which make flaw identification more difficult; the contrast between tubes which exhibit signs of minor denting in the support plates and tubes which are essentially free from denting present such circumstances. How denting affects flaw detection is described in Section A.3.5. By employing these techniques, identification of flaws is improved and conservative amplitude measurements are promoted. The Mix 1 traces which result from this approach conform to the model of TSP ODSCC which represents the degradation as a series of microcrack segments axially integrated by the bobbin coil; i.e., short segments of changing phase direction represent changes in average depth with changing axial position. This procedure is to be followed for reporting voltages for the plugging criteria of this report, even though it may not yield the maximum bobbin depth call. If maximum depth is desired for information purposes, shorter segments of the overall crack may have to be evaluated to obtain the maximum depth estimate. However, the peak-to-peak voltages as described herein must be reported, even if a different segment is used for the depth call. The Beaver Valley site guidelines for reporting EC indications require that conflicting results reported from independent analyses will cause the particular location to be resolved. If the largest voltage call exceeds the voltage repair limit and another analysis is NDD, whether or not an indication will be reported will be determined by a resolution analyst. If the amplitude measurements reported from the analyses differ, the larger of the measurements will control unless the lead analyst (primary vendor Level III) clearly establishes that the higher amplitude measurement is erroneous. Lead analyst review is required on indications exceeding the voltage repair limit for which the reported voltages differ by more than 20%. Exercise of this review by the lead analyst will be denoted by use of LAR (Lead Analyst Review) as a comment associated with the data base entry for that indication. Each analyst's original call A - 12
will be preserved on his individual report and stored on the permanent record optical disk for the inspection. This practice limits the uncertainty attributable to analyst uncertainty to 20%. A.3.3 Copper Interference In situations where significant copper interference in the eddy current data is noted, the eddy current technique could beconie unreliable. This results from the unpredictability of the amount and morphology of copper deposits on the tubes which may be found in operating steam generators. The above observation is true both for bobbin and RPC or any other eddy current probe. Although small copper signals have been detected, such as in R6C58 TSP-lH of SG 13 (see Section 7.3), significant copper interference does not occur in the support plate crevice regions of the Beaver Valley steam generators. This is confirmed by destructive examination of the support plate intersections on tubes pulled from the Beaver Valley Unit I steam generators. No plated copper was found on the tube OD within the support plate crevice, although some minor plated copper patches outside the crevice region were sometimes observed. Inspections with RPC and bobbin probes have shown good correlation for flaw amplitudes exceeding 1.0 volt; i.e., more than 50% of the bobbin signals identified have been confirmed to exhibit flaws to the RPC probe. This suggests that spurious signals from conductive deposits do not result in excessively high false call rates. Furthermore, signals judged as NDD with the bobbin guidelines have been confirmed to be free of RPC detectable flaws. Copper is a concem for NDE only when plated directly on the tube surface in elemental form. Copper particles with the sludge in the crevice do not significantly influence the eddy current response. To Westinghouse's knowledge, no pulled tubes have been identified with copper deposits on the tube at the TSP intersections - in contrast with free span tubing. If copper interference is observed at Beaver Valley Units 1 or 2, the existing rules and procedures for complying with the technical specifications plugging limit based on depth of wall penetration ; will apply. l A.3.4 Alloy Property Changes This signal manifests itself as part of the support plate " mix residual" in both the differential and absolute mix channels. It has often been confused with copper deposit as the.cause. ! Such signals are often found at support plate intersections of operating plants, as well as in 1 the model boiler test samples, and are not necessarily indicative of tube wall degradation. Six support plate intersections from Plant A-2, judged as free of tube wall degradation on the A - 13
O basis of the mixed differential channel using the guidelines given in SectiontA.2.5 and A.2.6 of this document, were pulled in 1989. Examples of the bobbin coil field data are shown in Figures A-16 through A-18. The mix residuals for these examples are between 2 and 3 volts in the differential mix channel and no discontinuity suggestive of a flaw can be found in this j channel. All of them do have an offset in the absolute mix channel which could be construed I as a possible indication. These signals persisted without any significant change even after chemicallt cleaning the OD and the ID of the tubes. The destructive examination of these i intersections showed very minor or no tube wall degradation. Thus, the overall " residuals" of both the differential and absolute mix channels were not indications of tube wall degradation. Examination of the detailed structure of the " mix residual" (as outlined in Sections A.2.5 and A.2.6) is necessary to assess the possibility that a flaw signal is present in the residual composite. Similar offsets in the absolute channels have been observed at the top of the tubesheet in plants with panial length roll expansions; in such cases, destructive examination I of sections pulled from operating plants have shown no indication of tube wall degradation. l Verification of the integrity of intersections exhibiting alloy property or artifact signals is : accomplished by RPC testing of a representa'tve sample of such signals. i A.3.5 Dent Interference 1 A fraction of the Beaver Valley Unit I support plate intersections exhibit corrosion induced ! dent signals. These locations, when tested with bobbin probes, produce signals which are a [ ! composite of the dent signal plus other contributing effects such as packed magnetite, i conductive deposits, alloy property change (anifacts) plus flaw signals if present and the support plate itself. The 400/100 kHz (differential) support plate suppression mix reduces the support plate and , the magnetite signals, but the resulting processed signal may still be a composite of the dent, , artifact, and flaw signals. These composite signals represent vectorial combinations of the constituent effects, and as such they may not conform to the behavior expected from simple ! flaw simulations as a function of test frequency. The effect of the dent on the detection and evaluation.of a flaw signal depends on both the [ relative amplitudes of the flaw and dent signals and the relative spatial relationship between j them. If the flaw is located near the center of the dent signal, interference with flaw detection ; may become insignificant, even for relatively large dent to flaw signal amplitude ratios. The l flaw signal in a typical support plate dent in this event occurs mid-plane -- away from the support plate edges where the dent signal has maximum voltage; thus the flaw in the middle l A - 14
. - -w - ,__ -,,,4.m .-- - - - . . -- ,~ - -
+
l section of the support plate shows up as a discontinuity in the middle of the composite signal. Some examples of such cases in the field data obtained from another plant are shown in Figures A-19 to A-24 for dents with peak-to-peak amplitudes ranging from ~4 to 10 volts. The top pictures in these figures show the composite signal voltages; the picturet in the bottom L half give the flaw voltages. For example, in Figure A-19, the dent voltage at 400 kHz is ,
~10.3 volts and the flaw signal voltage in the 400/100 kHz mix channel is ~1.3 volts. It can be observed from these figures that one can extract a flaw signal even when the signal to noise (S/N) ratio is less than unity. The question of S/N ratio requirements for the detection and evaluation of the flaw signal is answered by examination of Figures A-19 to A-24. In all cases shown, S/N is less than 1, and the flaw signal can be detected and evaluated.
The greatest challenge to flaw detection due to dent interference occurs when the flaw signal occurs at the peak of the dent signal. Detection of flaw signals of amplitudes equal to or greater than 1.5 volts - the criterion associated with IPC confirmatory RPC testing - in the presence of peak dent voltages can be understood by vectorial combination of a 1.5 volt flaw signal across the range of phase angles associated with 40% (110 degrees) to 100% (35 degrees) through wall penetrations with dent signals of various amplitudes. It is easily shown that 1.5 volt flaw signals combined with dent signals up to approximately 5 volts peak-to-peak will yield resultant signals with phase angles that fall within the flaw reporting range, and in all cases will exceed 1.5 volts. All such signals with a flaw indication signal will be subjected to RPC testing. To demonstrate this, one-half the dent peak-to-peak voltage : (entrance of exit lobe) can be combined with the 1.5 volt flaw signal at the desired phase angle. The inspection data shown in Figures A-19 through A-24 illustrates flaw detection and . evaluation for flaws situated away from the peak dent voltages. The vector combination analysis shows that for moderate dent voltages where flaws occur coincident with dent entrance or exit locations, flaw detection at the 1.5 volt amplitude level is successful via phase discrimination of combined flaw / dent signals from dent only signals. The vector addition model for axial cracks coincident with denting at the TSP edge is ! illustrated as follows: o l A - 15
~ , - . - - ~ . - . , , . . - - - . - - - - - - - , . - , - - - - - - - - . - - - - - . - - , , . - - . . - ~ - - - - - . - - - - ~ , - - - - - , - - - -
1 ( .where , R= Resultant Signal Amplitude A= Flaw Signal Amplitude D = TSP Dent Amplitude - one edge (Peak to Peak = 2D) . 0 = Flaw Signal Phase Angle (100% = 35*; 40% ~ l10,')
$a = Phase Angle of Resultant Signal = arctan (Asin8/D + Acos0) and R' = (D + Acos0)* + (Asine)'
For dents without flaws, a nominal phase angle of 180* (0') is expected. The presence of a flaw results in rotation of the phase angle to < 180' and into the flaw plane. A phase angle of 170' (10* away from nominal dent signal) p.ovides a sufficient change to identify a flaw. For dents with peak to-peak amplitudes of 5 volts, D = 2.5V and the minimum phase angle rotation ($x) for a 1.5V ODSCC flaw signal greater than 40% throughwall is predicted to be approximately 13*, sufficiently distinguishable from the 180' (0*) phase angle associated with a simple dent. Such signals should be reported as possible flaws and subjected to RPC testing for final disposition. - Supplemental information to reinforce this phase discrimination basis for flaw identification can be obtained by examination of a 200 kHz/100 kHz mix channel; the dent response would be lessened while the OD originating flaw response is increased relative to the 400 kHz/100 kHz mix. RPC testing of indications identified in this fashion will confirm the dependabilitp of flaw signal detection. A sample ofintersections with dent voltages [ phase angle 180'(0')
- 10*] exceeding 5.0 volts will be RPC tested.
A.3.6 RPC Flaw Characterization , The RPC inspection of the intersections with bobbin coil flaw indications exceeding the voltage threshold is recommended in order to verify the applicability of the alternate repair limit. This is based on establishing the presence of ODSCC with minor IGA as the cause of the bobbin indications. The signal voltage for the RPC data evaluation will be based on 20 volts for the 100% throughwall,0.5" long axial EDM notch at all frequencies. The nature of the degradation and its orientation (axial or circumferential) will be determined from careful examination of the isometric plots of the RPC data. The presence of axial ODSCC at the support plate intersections has been well documented, but the presence of cellular corrosion which includes elements of circumferential ODSCC at the support plate intersections has also been A - 16
1 i established by tube pull in several plants. Figures A-25 to A-27'show examples of single and multiple axial ODSCC, Figure A-28 is an example of a circumferential indication related to y ODSCC at a tube support plate location from another plant. If circumferential involvement results from circumferential cracks as opposed to multiple axial cracks, discrimination between axial and circumferential oriented cracking can be generally established for affected arc lengths greater than about 45 degrees to 60 degrees, well below crack lengths likely to be - subject to propagation due to flow induced vibration. Pancake coil resolution is considered adequate for separation between circumferential and axial cracks. This can be supplemented by careful interpretation of 3-coit results. If a well defined circumferential indication is identified at a tube support plate location in the Beaver Valley steam generators (>60 degrees circumferential extent), guidelines for RPC interpretation will be reviewed and consideration given to supplemental inspection techniques for resolution of the degradation mode. Tubes with circumferential cracks will be repaired in accordance with Tech. Spec. limits. The isometric graphics which are produced to illustrate the distribution of signals in a TSP may sometimes exhibit distributed extents of flaw content not readily identified with the discrete axial indications associated with cracks; this may occur with or without the presence of crack signals. The underlying tubing condition represented by volumetric flaw indications is interpreted in the context of the relative sensitivity of various flaw types (pits, wastage / wear, IGA, distributed cracks) potentially present. The response from pits of significant depth is expected to produce geometric features readily identifiable with small area to amplitude characteristics. When multiple pits become so numerous as to overlap in the isometric display, the practical effect is to mimic the response from wastage or wear at comparable depths. In these circumstances the area affected is generally large relative to the peak amplitudes observed. The presence of IGA as a local effect directly adjacent to crack faces is expected to be indistinguishable from the crack responses and as such of no structural consequence. When IGA exists as a general phenomenon, the EC response is proportional to the volume of rnaterial affected, with phase angle corresponding to depth of penetration and amplitude relatively larger than that expected for small cracks. The presence of distributed cracking, e g., cellular SCC, may produce responses from microcracks of sufficient individual dimensions to be detected but not resolved by the RPC, resulting in appeent volumetric responses similar to wastage and IGA. A - 17
For hot leg TSP locations, there is little industry experience on the basis of tube pulls that true volumetric degradation, i.e., actual wall loss or generalized IGA, actually occurs. Figure A-29 illustrates the RPC response from a Plant A pulled tube in which closely spaced axial cracks (lower portion of the figure) produced an indication suggestive of a circumferential or volumetric condition. All cases reviewed for the APC present morphologies representative of ODSCC with varying density of cracks and penetrations but
~
virtually no loss of material in the volumetric sense. Appendix C of EPRI Report NP-7480-L, Volume 1, Revision 1 provides a more detailed discussion of RPC response characteristics consistent with the APC database. The available data in this report indicate that RPC l responses < 150' in azimuthal extent and > 0.2 inch axial length are acceptable responses for RPC applications. For cold leg TSP locations, considerable experience has accrued that volumetric degradation in the form of wastage has occurred on peripheral tubes, favoring the lower TSP clevations. , Therefore, hot leg RPC volumetric flaw indications within the TSP intersections will be l presumed to represent ODSCC, while only peripheral tube, lower TSP locations on the cold l leg with RPC volumetric flaw indications will not be so characterized. A.3.7 Confinement of ODSCC/ IGA Within the S,upport Plate Region In order to establish that a bobbin indication is within the support plate, the displacement of each end of the signalis determined relative to the support plate center. The field l measurement is then corrected for field spread (look-ahead) to determine the true distance i from the TSP center to the crack tip. If this distance exceeds one-half the support plate axial l length (0.375"), the crack will be considered to have progressed outside the support plate. Per the repair criteria (Section 10) indications extending outside the support plate require tube repair or removal from service. 1 A.3.7.1 Crack Length Determination with RPC Probes The measurement of axial crack lengths from RPC isometrics is presently a standard portion of the Beaver Valley site EC interpretation practices. For the location of interest, the low frequency channel (e.g.,10 kHz) is used to set a local scale for measurement. By establishing l the midpoint of the support plate response and storing this position in the 300 kHz and 400 kHz channels, a reference point for crack location is established. Calibration of the distance scale is accomplished by setting the displacement betweer the 10 kHz absolute, upper and lower support plate transitions, equal to 0.75 inch. A - 18
At the analysis frequency, either 300 kHz or 400 kHz, the ends of the crack indication are located using the slope-intercept method; i.e., the leading and trailing edges of the signal pattern are extrapolated to cross the null baseline (see' Figure A-30). The difference between these two positions is the crack length estimate. The slope-intercept method, studied by Junker and Shannon W , utilizes the total impedance data profile to predict the actual crack length from pancake EC data. This technique, which is illustrated in Figure A-31, yields measurements which are less affected by the shape of the' crack than does the amplitude threshold technique commonly used in field measurements. The measurements obtained consistently oversized the true crack length by approximately one coil diameter. Thus, for calculations using crack lengths, the field measured lengths should be adjusted for pancake coil diameter. Alternately, the number of scan lines indicating the presence of flaw behavior times the pitch of the RPC provides an estimate of the crack length which must be corrected for EC field spread. Figures A-32 and A-33 illustrate the identification of the first and last scan lines of the linear indication from which the length of the underlying flaw can be determined. A.3.8 RPC Inspection Plan The RPC inspection plan will include the following upon implementation of the IPC repair limit:
- Bobbin voltage indications greater than 1.5 volts for a 2.0 volt repair limit, or greater than 1.0 volt for a 1 volt repair limit.
- A representative sample of 100 TSP intersections, as applicable, based on the following:
- 1) Dented tubes at TSP intersections with bobbin dent voltages exceeding 5 volts.
! Artifact signals (alloy property changes) with amplitudes potentially masking flaw signals greater than 2.0 volts for a 2 volt repair limit, or greater than 1.0 volt for a 1 volt repair limit.
l m EPRI TR-101104, W. R. Junker and R. E. Shannon, August 1992 l A - 19 I l
4
- 3) Non measurable depth O.D. indications (UOAs) with amplitudes greater than l
2.0 volts.
- 4) Indications not reportable (INRs) with amplitudes greater than 1.5 volts.
Considerations for expansion of the RPC inspection would be based on identifying unusual or unexpected indications such as clear circumferential cracks. In this case, structural assessments of the significance of the indications would be used to guide the need for further RPC inspection. A.3.8.1 3-Coil RPC Usage Beaver Valley site standard practice allows for use of 3-coil RPC probes, incorporating a pancake coil, an axial preference coil, and a circumferential preference coil. Comparisons for ODSCC with bobbin amplitudes exceeding 1.5 volts have shown that the pancake coil fulfills the need for discrimination between axial and circumferential indications, when compared against the outputs of the preferred direction coils. Pancake coils have been the basis for reporting RPC volt,Jes for model boiler and pulled tube indications in the APC database. These data permit semi-quantitative judgements on the potential significance of RPC indications. The requirement for a pancake coil is satisfied by the single coil,2-coil, and 3-coil probes in common use for RPC inspections. Supplemental information, if needed, may be obtained from review of the preference coils on the 3-coil RPC if desired. A - 20
t TABLE A-1 EFFECT OF MAGNETS ON RESPONSE OF ECHORAM BOBBIN PROBES 7/8" TUBING STANDARD 0.720 MIL PROBES AVERAGE AMPLITUDES @ 400 kHz With Without Ratio Magnets Magnets With Magnets /Without M=W3 ASME 4 x 20% 4.04 4.01 1.008 4 x 40% 3.42 3.42 1.000 4 x 60% 3.73 3.74 0.993 4 x 80% 3.92 3.94 0.995 4 x 100% 5.97 6.01 0.997 Support Plate 6.60 6.35 1.040 WEAR STANDARD 100 % 5.87 5.71 1.028 100% 5.83 5.84 0.998 100 % 5.68 5.75 0.987 100 % 5.86 5.65 1.032 0.5" EDM STANDARD 20% - - - 40% 0.78 0.79 0.988 60% 1.92 1.93 0.995 80% 2.61 2.61 1.000 100 % 73.43 74.06 0.992 A - 21
TABLE A-2 MAG BIAS VERSUS NON-MAG BIAS PROBES COMPARISON PLANT R PULLED TUBES (SUPPORT PLATE SUPPRESSION MIX) Mag Blas Non-Mag Blas % Change PULLED TUBES (B&W): 3/4" TUBING,550/130 KHZ MIX 0.38 0.37 +2.7% 5.23 5.06 +3.4% 4.10 4.13 -0.1 % 2.11 2.07 +1.9% 5.38 5.34 +0.1 % 3.26 3.31 -1.5% 0.18 0.82 -1.2% l.06 1.04 +1.9% MACHINED HOLE (B&W): 3/4" TUBING,550/130 KHZ MIX 5.24 5.40 -
-3.0%
5.43 5.54 -2.0% 2.74 2.76 -0.1 % 11.60 11.78 -1.5% 19.82 20.17 , -1.7% 4.67 4.80 -2.7% A - 22
PROBE' COMPARISON 1NRUD4CC Or OtAMETER (WIX CetL) 50 c J g 40 - c E w Q g Jo -
+
E i 5 o Q w 20 - l E o i z - l u l 5 a to - 1 j g . w o
" i e i ,
i 0 to <a I EDDY CURRENT MEASUREMENT (720 PROBE) - V0LTAGE _ l O 740 + 700
- 680 l
Figure A-1. Probe Comparison. A - 23
t T\\\ 90' typ
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- w. 6 I
T -
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i g r
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Figure A-2. Probe Wear Calibration Standard 1 A - 24
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so. als a v I aev 1 s.S. .se ou a at ia.es aos ou a a u g 3, g ,, g ,s Initial placement of cots EoEsEa M , S/S 681 f losim
~
m f .e. es lil llau [ 7 '
& omon, tre I to l 'lii s,as as.sviiu iruiu
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-_ -- 2.= mi ,,, . .n ., i,
. ) t I
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5
- ;E > >
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- n. i=ai a 3.n i.s . . . .
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. a ) Final Placement J 0f f k Dots semia ecum e o
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.., ,. m ,, ,,, ..,. i., 3,, ,.. . . , , . . .
. . . cm ,
( ) ( ,=. . . St % 4 _% % **
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- ls } % s- w 4 =
i
/ g ( 3 i Figure A-3. Bobbin Coil Amplitude of ODSCC at TSP.
A 25
3e mis a v l- os 6 7 5.64 ese she os a n s.48 Jos ou os 3 el g . g , g ,, initial j Oct 3 61 E 6 $c ) f s/s I mit seem l o Placement l i :nitial la l + se l:I lital , 001 Of0ff; ftC l TDI l m ! placement setze 23.Siinue.c ifaasa-L t I l
~
l vpp 1 . 75 M e1 ?!I Ypp 1,73 M 71 $75 J _ ' I w 4 . w --.==al m _. M % b '
/ l l
, 6. 77 100 D e CM S M 3. 2 1:5 als 1 2e
-F lottlal 1
Oct Final
<[ Dot Placement K \ Placement In ti4l Placement p g I
i son 1 i ,,, ..n enis. a.ei
.a .. . ==.
== v., u m si os 5- * " a;"l '"'
l / me , a > . s e es
/< , 4 w;
'o m b- **
i _y s 4 .c s ( , , l I I / e i Figure A-4. Bobbin Coil Amplitude of ODSCC at TSP - Improper Identification of Full Flaw Segment. A - 26
1 l [ Is i mis v cm a v ...: we oi cm a u 3.4 aos o. as e g g g ,--
- l, Initia1 i 3 ..- 3 D + II D .
r Mi t tal Dot :ih ses it soeer
- Placement [
k Dot in l4,s g,g ging j, placement s a m,,, y L - sms u.sitive puing I
. I . I i
j vM l .M E 122 .4s vM 3.4I e les 1R
- L / \
/
w u - l
" ~
J> % G~ l h I 5 u _ 1.7s see ou os s ei 4.21 sis nie a
- Initial ('I
\
I"iL183 Dot \ Final py i
- J . -
Placement Det Placement k
- -, f 1.
sons, e asui s. _
- a rir ini os vM 2. e e es see ww 2.*4 m tu c.=
i re. . . . , .
~
1 ,
/ > > .
.cw
% ~, a ; :
. t .
% C r -
\ ) ) %
\
Figure A 5. Bobbin Coil Amplitude of ODSCC at TSP - Improper Identification of Full Flaw Segment. A - 27
THROUGH WALL VS. DEGREES ts a t as : as : as : as a tie." " r " o "'i'"e"m"m "" . . . ou .# in . 1 3 es s3 st 54 13s 8
- 2 s er s2 s2 53 ist e 3 s es n ss 52 t3e e 100'- : 4 2 es s M si ss e s is se se ss se see e
; a le si se M 4e, let 907
. p 5 es 37 4 i. e.
- e 24 53 es se 44 843 e s 27 54 es ss es i+4 e
- l' 3e ss or see 43 ses e j 00h : it 33 se as les 42 ses e J - 12 38 s7 es noz 45 ter e se M 64 3 39 toe e
( 707 i3 3s 34 4 ss e4 so 3e i.s e g - as 45 es as ses u ase e
. is os et es tes 3s ist e s2 s2 ser M 652 e I 60h tr s2 se ss as en see 32 is e g - ts se s4 et les 31 154 e
'l -
M si an sie 2s iss e 50-2: u un ::: 2e iss e 0 - 22 s7 sr Fe 112 2s tsi 8 23 M M 17 113 2s Ise 9
- 24 73 n is 4 23 iss e I 40' -
- 25 is M rs its 22 ses o p -
* . 2s 79 FL 74 Ils M ist 0
- 27 e2 72 74 187 le is2 4
; 2e a r3 13 tte 17 is3 e X 307 - ts se 74 72 lls is is4 9 30 st 7s 71 IN 83 las e 2 31 M M 128 1 IM gg", ,
- uu M,, es i n i.2 iu e.
- M - in e iu .
- n u ic.e. n- i24 s in .
3s 99 se M in 4 in e 10 in 2 iri .
- ei as u se uo in in .
=, nn in .i in .
"O ......
20 40 60 80 100 120 14 0 160 100 25 g g 52 jg
- j s p CEcRES
- w aa ist
- 818 8 42 ss er ss in e air e NIN 43 ss M H B33 e tre e a m u u es si iu o in e 16 SR 33 10m 06 6m 116 2m Figure A-6. Bobbin Coil Calibration Curve for 400/100 Mix.
t 1 A - 28
l I l l 40 7tlX 1 V 00 6 V 3.00 1:s IIII 1 14 6.se 400 Ou 041 3e , E 1 6 g ses inutt IM l+e.eslil lati
- ~ ~
m cxTos7 x l rtu pl s,cro --- ini e inang _J _
- 6
- ~
t v,, i.i> - V,, .. i.i 2. r s- 1
~
T N .W > h J t 4 \.. % s 7 s te.as aos no os 3 as ae.n see ou os s ss EP est stages 3 setta gas Vpp 8.82 129 et Vpp 1.31 1,2 gg fe. 312123:33:u stat f cm rue e a s . s s r e b & 4 4 *
- 4 1
>J
> '>=-
l Figure A-7. O.D. Origin Signal With Phase Angle Greater Than 0% Intercept on Calibration Curve. A - 29
l l l - 1 MIN 1 V CM s V 2.M 1:5 MIN 1 le 6.41 ese the 011 29 g 3e een tu r S/E IleET 1, ein I.e.selil liu unti itn I ttM In
,g, ePED ---- in/sec reAIN s
l - _g ) y [ vpp 1.e3 - 164 sa vpp e.se m 167 es I W w -d d t.
% L
~ -
r 4 "s N l \ l 200 the 01 3
\
e1
~
17.78 20e Khz CM 3 et 17.78
~
- I h t J ,
1
, -? teosts BCaes: $ setti see
- 6 eg m s.1 as es: start esta Vpp 1.29 m 1H se Vpp 1.29 M IM test 3 8 3
\ fM4 & 3 3 4 5 6 7
\
d' d' g s *
> % > % ,se I i l i Figure A-8. O.D. Origin Signal With Phase Angle Greater Than 0% Intercept on Calibration Curve.
1 A - 30
42 NIE 1 V CM & V 2.58 til RlX 1 11 4.79 ese Kha CM 1 21 igg SC rac A, . att
&c -
5 "' I 1H 1.e.e31:1 lin
~
ftn l ttC IITENT Q 3g , , _ .$P[to 21.15l in/see tralw I 4C - = 7 l sc __ - Ypp 1.10 - l'114 26 944 Vpp 8.54 M 35 874 N ~* 9l 1 N 1 %
~
- R, ~
3 %, P m 15.31 290 Kha Ot 3 78 15.et les Kha CM 5 68 Ede --
, J
}- l 3N m
IN k aranei
/ y Vpp 3.33 laias 12 343 Ypp 2.21 M 332 ta n a.
se es:$4:n atts TSM , (eit i TDI w 1 \ i I 4 __g g '::
~
t < s F F, P i i i Figure A-9. I.D. Origin Signal Observed in Plant A-2 Support Plate (400/100 Mix). A - 31
l l as eae e oa t.as see o. c" *
- 5 m o a cm. .
Bu m a mut e enema a
)
1 e ausma in un. w as tems, m
"*"" """' *** 8 88m" na 1.e.es 1 1 [in C'*f 18 I 18 P g
emesms'[pesetal
-a i I es I asia. SPEIa e.2% lWeec b la J
t 1 h J (. 6
/~ ;>
t i MBAl. VIO e.m CaetaBFEMNTIn. DETs M SEE nas I
. ?
me l
! I -.
usu. saux nn
.i assas, ext. e.es sa :
! j 1 I
i i
%JK .
i f Figure A-10. RPC Confirmation of ID-Oriented TSP Signal as O.D. Flaw. A - 32
l l l
,. ~ . , .. ,, m .., " ' "
M.% _84P M**** wans "hu p-Q
- s ,,
-- y .. . ..., .
- L 3 1 3=
-< x a-
- l , . . . . T. . .. 1 ,,, ... .
F ,, a I 4(
+ w i
! 6 l les var t .13 M ft me tedhe s.ehems eus Tuo 3 99 M te ,..7...
5 j t = 1 -
= _ f _
=
I b 1 Figure A-11. Placement of Dots Marking Lissajous Traces for R19C86 - Analyst 1. l l A - 33
.e oav s es .e w a e is is.ia aos ou a : .e , , ,
I
~
I h 185 14.51- .lig
~~~
g
/ Omtri re I rig ) T
_y , EPED 1...... iu se reang
\'
4 - , 1- ____ _._ w i mu ,,, i= . = = bI 3 1 I .)
~l. 2' r ,
=__
A- 1 l 1 1 I F
.. i.-.. .e .. .. ... . i, 1
l r- T yl - '
-- g
. . . . .. .. -. 7. . ,, .,
') J [ } =
=
, !i .
.i
-- a 1
- e = *
, T I F 1 : : -
Figure A-12. Placement of Dots Marking Lissajous Traces for R19C86 - Analyst 2. A - 34
1 j oe 1 sits 3 y 08 6 v 3.22 ees cAs os 1 47 7 83 20e sha os 3 og -
@ 14 @ I Qa
? 5/6 Ulf ilt.g f f- G til l 4 80 l:l 'g OTDeil fIC ] TDs l 1u j= i SPtIB 113.321Intese ftala
=
" ~
~
{ < vpp 8.11 g M 833 vpp g.se g ggg g3g
-~ q I 2 I I
- l _f L j l
". }( m
- = n > --
F 12.88 l i i its tha Qt S 69 3.e6 1S als 3 13
~ ~1~
Flaw I l
- in u I Km9 sett a ese
- v,, e.n a ns sa v,, e.e e .e saa a8- * ** a 's i =
c ...
- <=. . , . . . .o
- -,s - - } f . . e i
.i w -
%s M = *
= i
,. . se a a w
l Figure A-13. Bobbin Coil Arnplitude Analysis of ODSCC at TSP. A - 35
f 24 8.41 2gg ces Os 3 M . , , alt 8 y 00 6 W e.06 ese EAs 01 1 , se I3 . < m i (g <-
- N if IILif la 1 +e .se lil Jt4
- 3
, otetti ruc l ra J i
y -, M 11.25 tin /aes itaal 3
~
-( --
h" I 33 Ste vpp e.ee M S2 723 vs, 0.08 y l i
- ( q 1
)
. J
_n
~ % N ~..
- b. .
s > # % e
- . ===
( g
$3 1.61 1iS MlE & le
- , . $.93 100 D s 08 $
~
~
D F1av M h Y ~)~ w-s man, e in e n
==,
= no w e n,m n in.
- l ,, e .w sm $s un v. e.* tem
( $ ,=. . . 1 . soi1 i f * ' ' '
~-
% 4 ;,
; r.__.- -
r a i e
- . I N Figure A-14. Bobbin Coil Amplitude Analysis of ODSCC at TSP.
{ A - 36
M , siis i y Os 5 y e se ses ou ce i 22 7 if 200 o u 01 3 n
~
l l j te m i i i in f e.selil ilia i fJfDT ftc l fas j m SPEED _23 lijin/soe iteAIM p = J
~
7 a ,
- v. ..ra e in .s. ,,, i.2. ies ,.
f I I I I I W 4 4 i f % ?= s
+ W I t i.e ies ou os s se i.u sis nie se Conservativi .
Approach I for
- Placement of n Dots -
I l - es== ,
, ec== e ..
.I v. e.n e is: es y, e.n as me i v . ., .
f n I I 5 rus . , . . . . ,!.i - 1 4 % % 3 <= s u
- P W m apr- E l
l l \ \ % Figure A-15. Bobbin Coil Amplitude Analysis of ODSCC at TSP. A - 37 w _____-_-_-_-_ _ _________---_-__-__-_--____-____-----____ _______-___ _ _ _
l ' l l l
.i. . . .. ... ... , ,, , , o ... ,,, , ,, ,
pi , , . em ein six J, 7 n .it -!
- . ~~ ' r3 i . .. , ... ~'s DTUTI K.E l De ; l i
r,a ma .. . .. .. . ; i E 400/100 Absolute l 1- . l ... 2.is xc in .= . a.ia as m
?
~
? I I (. & l / l 2 m <= r5i m ;
I 9 i N l \#i (
/ i s l P i r g, - nu i.i ais i .s i is a m .: n4
.i ,,
.=
. l
- f m , ,,
T _. . 400/100 Differential enssi e met v a.a ocs iss es = s.n as n as = a a i es: mis i=.
.- ~~
I i ( ) i ( ....'..,....'l..,. l([ a ~..e E
* \ + , 5 >
;
- i A 5 i P 1
% J \
. y ) l Figure A.16. Example of Bobbin Coil Field Data From Plant A -
Absolute Mix With No ODSCC. l A -38
t
'23 ce a e , als 2 < s t 64 *H CAs J" I i 18 1 6 62
[ 2.6 El3 2 ) ), e gg _ g , _ ,e g U
~
l-b,5 T~ M
. % [;M .J El i el 26 } l
- -- --- D1?If; Mc ! DG ,
sme : . . . ... , .
~
400/100 Absolute E l xs ..
. 2... u . i.., = 2n =4 b I
(
! 5 / Nl !
?
. -. m .
=x uo <- -o-_, .
e . m- --* i r I i -- ( ! > ( l ( ., g( ,u ns .a i ., is.. Ja . i a 5-- - -
- 400/100 Diffarential
. .i . . ! .. . M D -
l I __ U . x-,.
-c a' +a L.- - 1 i ... ..., as isi .. . s.., xs = = ~6 +n 1,=....,'a.."*,=
- 3
/ i 3 / I $
L g . w p i 4 1
--C',' '
lp . a- w
+ a ,- i ..... .
f, , ( i d ( ' 5 1 Figure A-17. Example of Bobbin Coil Field Data From Plant A - Absolute Mix With No ODSCC. A - 39
23i o, i . . . i s a . . . ,. .. o, o, i 2.. s . .a ,.. ,i i . , ., u i u .. , cm, _. 400/100 Absolute g,g
~
,fI i i,. s.=, .w .q l t usas, anc oe
-- l 'y m en ...... .,...
s ; ,
;- -_ 4 C / :
V
/
- p vee 3 34 MC Je .a i vee 2.1. KG 291 es i
{ i l ! ( -= l f w
': = :=> % '
at=' 3=G A A r
~~~
r I i 'T Ii !'
- 1. 1.5 811 E 1 2T2 19..S 200 Os 08 3 21 9 '
5--
-- \ 400/100 Differential . -. ~
i
... - i n . , -
-- . ..., x. i.. .. . .. =. .. ,
<=.'..,.l.,.
l
~~
[ ) l [W ( l [
~:* * .
- .. j .
- v - - . ... .
j- .
) l } l l T .
Figure A-18. Example of Bobbin Coil Field Data From Plant A - Absolute Mix With No ODSCC. l 1 A - 40
es ce a v Os 8 m 8.64 8:6 AIM i 288 tl . M ees O w De 4 2M NR t if ISW I I Irg
- "' ~ *** ommt as I as i gutg3 ... .., Iw eeg 4
- - vpp e.68 E IM M vpp it.29 OES 198 GB l k I k
, 3 m m M i v v + w l b -
\
l ! ' l 8 , ,5 . . ... ,,--
""" % Gn e-o.
samm e em ese
,,, i .n a se me w i.8e ses :: a **a- = sei.asime i
l
==
( l ( ,es i , . . ii. ? , _, -
- . . i, ..
> - a w 5
- ) / } - - ~ i l Figure A-19. Example of Bobbin Coil Field Data - Flaw Signals for ODSCC at Dented TSP Intersection. A-41
l l l 36 mas 3 , i Os g v s 3: 1.g als : e. 61 ee. W os a og
" r 1- *co.
tGao.t j
; p.
pq . . - . OfDftl Es j te -
.. . . o
-- - . 3 1. e n is. a. . in =s to
( i y t i y x s y k e . x i 4 i as > - 1 i , / i % s.t> i s nas ee 63 .e. om os : .:
.)
-- L l
I -
. I
. .n
- - . m ee. ,
I ! .. i . u s u i., ii. . ... as in - . oi .= ( ' f / f . .....;..,...
- %, b w A 0 ; i
< v 4 + . .. ..
} .g
., f., , . . .g = ,
-i .i w- ;g -. ..
Figure A-20. Example of Bobbin Coil Field Data - Flaw Signals for ODSCC at Dented 'I SP Intersection. A - 42
1 i e6 Os i e i Os i n 4 79 1.5 mit i 34 it H ese ce os g ggg
- 4 9 -
aca in t/s it igues b - - 1 i I! @ a p amrv sa i ce i wars . . . . .. y e ,
~
m - .. tn e iis u .. e e, as is, a
. .( )_ ; g i , ,
_ f , - - 1 r- - i __.g ~ - s l
- , _ _ ! l 5 l l I s
- ! ..n i,i mis i w is.H .se o. ai i ni - 1, _ _
- a _ _
I
. j -
m
,e .
w e.n me no w e.n ass in a ww=**=.*.= _.
~
p l j r . . . . .. ..i 7 C 1 *""""'" % ' ' e - 7 e . . . i 3 ( $ j Figure A-21. Example of Bobbin Coil Field Data - Flaw Signals for ODSCC at Dented TSP Intersection. A - 43
os a e . 7. til uit t 34 11 6e e De Oi1 818 e6 4 Os a v
. a _- -
- iEMIR q : -b .,
[
. ~
j
% onent us a ce i
"_ < _ -.=
.a veo 1.31 ES 4 .R I , - , vpp 3.53 M te?
'f i -
> : i >
- _. % % 8, I U
- T v T =:t
- _ _ t 3 1
.i 1
in _ .. .. ... 3 is P- me
- s . e. ,-
- j ,,, .. - .. ,,,....i. . - - = '*;,=; '-
4 j) i i ) .
. . ii. i
- J
- #-) 5 ix ( T
- i Figure A.22. Example of Bobbin Coil Field Data Flaw Signals for ODSCC at Dented TSP Intersection.
A - 44
( l l 1 l l
)
44- 04 i, Os i a e es ist mis M i3.51 egg gy. Ce i f1 l
- -- un i. iin
- ,_ ; l n ines:
.~ ~
t i iii g
; a .
; y cnonises 1 asi J L.
6 spas [.. w ,
+
F s
.- ., m . . an e i.e a . s ., ans is, a
)- l ?-~
I N__::=e-
'h._' V' 2 '
b l
. e.
$ I iil ase i
\ is s.a.
l l
.se o. a i n
, e -
~_. m.
. sam . u .m,
= e.m eu me w e.n en n a w a .m* .
}z_
@s.
= .mi."[l..,..!
l g' } - j 3 I I lll,! l l l l l l l Figure A-23. Example of Bobbin Coil Field Data - Flaw Signals for ODSCC at Dented TSP Intersection. A - 45 L . _
, ai, ei. . e. i.s uni it s.m o. m i n se.
ioner
. . E
~ '
= l l !al ,h5
- J F cmmi as I on 1
. mus t.....? w e
-- .. J '.
; -- + g r
. =su e in m =..m as in a
~
5 n
- i /
_ 9 5=-e w _t== e
- W i W ==* C
- ) i 4 I (,
- ... its osi is s.m .se e. e i n 4 m*. - seem e erets m.
- w e.n ea w w e.e sus n a " " ;"' " '"
[ - - (_ D -
- 7. l '!'!'ll
. i.
g g
- 3 a . . 1 1
Figure A-24. Example of Bobbin Coil Field Data - Flaw Signals for ODSCC at Dented TSP Intersection. A - 46
. . - .. _ _ . . ... . ....., j
- , . . - - , .. . m. _,__ ,
*# * '8 s a v tem . 3,e
' I M ** *
- n se u,, , l seuemamp . es l
i P I n [f 4.w .. .. . . . . . . . . . . , f l
^^
7 o u_ m ...-... . f- ~ , ,,, g l n = .. .. l ammmanen . ake a wannamaan e
* ====am . nua ,w,. .
1 i > detec-Eceynet: Analysta ( , lusert as pr a at MD I J i f Figure A-25. Example of Axial ODSCC Indication at TSP 1. A - 47 l
l I l l - 1 _J y[ .
. . .=.
e tus asset a es isri
==s - ==i=> F= i sei. ng
- - even wiwi -
L I .- T l mens eine asi a se isw =
- A
~
- eu e in
_V u - ...... .. s stemwnensa arti u em
; , t e
{ j b
- w.e.es
.e.m ans
- ~ i una me
- mis av. e.m a ;
r ! Figure A-26. Axial ODSCC Indication at TSP - Plant A-1. A - 48
at Os a , 6.8e 3ER 88 013 N e 4 l >
- e o esse es i e e esserie, se 9 58500mm me , ss.gf
?
- m. e sus sema. a seem mamme ame am m I e I.e sol.I N
Q i, ,,,,,, g *Ie 1
- yl seau R miens tiet sta EM E ** " H lw ams i
F
" ~
& l ets a ess 1
l w e.e 1
- . 1 I
8 3,33 I
- j. l ,
Cle684 GTs 04 m i-I P
- l. [ eie.er l i gA- ...
- , mi. n
- - L c i mia en. e.m is i- .
[ ! \ 1 l l l Figure A-27. Axial ODSCC Indications (MAI) at TSP - Plant A-I. A - 49
.., e u ans i i = * **
\
- s. i e .s g e M 414 yee . et ufattet
- MW
.<. u u
f \
\
[ .. .:. . .. .. w_ sr s .s f
"~~ .e. M , F '
q \ b_' = . . " ' . OD
~,
w is. .a i ,= s 1 T".%
- ,f,, 3 lf , a ' l j ___
u seus
' 1--d, 74 ; ~, c . ,,-- - - -
, ,,, i ps a un : an **
. as M=
,,==-'.
i
, pan - m usenes - set 88 1 !
k _4m --
~
~
..eeeeeeee a
W:_- - w sui sai e '.e.m
=' N sil 5 O l
ma m 8W" asas YY mas Figure A-28. Circumferential ODSCC Indications at Support Plates (P A - 50
30 CM i V CM 2 V 14.04 400 ths CM i 44 e 4 ) >
,,n.,.
9 SOfffitet N3 /4 1 letJT j
...n.
. - mm m. sr 9mm .siers,uiii . tin . .. . .i ! , i u .-
mmi ea ! v.
,,,,, ci.e uia ram se .= w.- l c u f
1 f' ,,, -
~
. t ,. - ,,
~
J ~
' 4 k _; i l_______ _ ~
4 #- 1 I { $' W
- - /
6
~
#s i i
.,,,g, 'k' :
ciamuutis ext, se as es C
/
/5 e--_,-' ,
p- \l L J g- ,, z 8.05 Q r Asist iteCE usr ar, e.n sa s
/ f 1
,.73.
- Top. . g. , .
,c~
f , Ii
':b ,
a
>4:7 Sarfm
,n.
W g2
;y,i
.y 1 d'$
)
3,:
'h 170 140 120" q .,
Mag. 3X Figure A-29. Plant A-2 RPC and Destructive Exam Results for Closely Spaced Axial Cracks. l A - 51
i, c,, , , .., i. . i = a w a m "li
!- b. l ._..b. i. i na aie trer] e i to i M
'j h I
peig kisclasia spets le ai!weee itananl 1 [ r N-h I JE [ asia ,im 3 a.wetsania en. ai ses , s I' _
, n. . .. ls>4.3 naim fandB
. cn . e.m is ,
/ ; .
Figure A-30. Slope Intercept Measurement of Crack Length. A - 52
i l I 1 I l l
.....................................................+.......................................... .
...........................................................I............................................... ..
..................................~..............-............. .......................
l
-- Inflection - *
...................................................................V.......................................................
~
= Threshold
..............................................................L......................-................... . . .
j Slope intercept 3 2' -1 .D i - 2 3 Probe Position / iinch'i 4 Figurt A-31. Techniques for Measuring Crack Lengths From Eddy Current.
)
A - 53 1
is o' i e m., e. = . . , , , , , am
.... ', " ""i A e== ..
a*a= O" 'f! .",,, vig
= i .ni.i
""o a DTDf th I rm l M
"*' '- Ife'ame neck i.. was . .,i ny ;.,g
) '= s u sur :=
6 r L ,)h -
,.a / 3 7
e.u 88 Asr . Figure A-32. First Scan Line Flaw Limit. A - 54
l 1 l l I 1 i I i i, ... im .. is a m a m m ae ..., n _a_:== : M !
.i-.,........
w ==..n. i. i ,i s i a.. j , , , , ,
.. 1,. .. ,,. ...
- s. vi fu
. .. I. re
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Figure A-33. Last Scan Line Flaw Limit. A - 55
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