ML20236Y112
| ML20236Y112 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 07/31/1998 |
| From: | WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20236Y107 | List: |
| References | |
| SG-98-07-012, SG-98-7-12, NUDOCS 9808110177 | |
| Download: ML20236Y112 (82) | |
Text
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WESTINGHOUSE PROPRIETARY CLASS 3 SG-98 07-012 1
4 FARLEY UNIT 2 1998 VOLTAGE-BASED REPAIR CRITERIA 90 DAY REPORT July 1998 O
Westinghouse Electric Company Energy Systems Business Unit Nuclear Services Division P.O. Box 158 Madison, Pennsylvania 156G3-0158 9808110177 980807 PDR ADOCK 05000364 P
9 SG-98-07-012 1
1 1
FARLEY UNIT 2 1998 VOLTAGE-BASED REPAIR CRITERIA 90 DAY REPORT July 1998 e
O q:\\ ape \\ apr98 \\apr90 day. doc
FARLEY UNIT 2 1998 VOLTAGE. BASED REPAIR CRITERIA 90 DAY REPORT TABLE OF CONTENTS Page No.
' 1.0 Introduction 3,3
- 2.0 Summary and Conclusions 2-1 3.0 EOC-12 Inspection Results and Voltage Growth Rates 3-1 3.1 EOC-12 Inspection Results 3-1 3.2 Voltage Growth Rates 3-3 3.3 Probe Wear Criteria 3-5 3.4 Probability of Prior Cycle Detection (POPCD) 3-6 3.5 Assessment of RPC Confirmation Rates 3-8 3.6 NDE Uncertainties 3-8 4.0 Data Base Applied for ARC Correlations 41 5.0 SLB Analysis Methods 5-1 6.0 Bobbin Voltage Distributions 6-1 6.1 Probability of Detection 6-1 6.2 Cycle Operating Time 6-2 6.3 Calculation of Voltage Distributions 6-2 6.4 Predicted EOC-13 Voltage Distributions 6-2 6.5 Comparison of Predicted and Actual EOC-12 Voltage Distributions 6-3
' 7.0 Tube Leak Rate and Tube Burst Probabilities 7-1 7.1 Calculation of Leak Rate and Tube Burst Probabilities 7-1 7.2 Predicted and Actual Leak Rate and Tube Burst Probability for EOC-12 7-1 7.3 Projected Leak Rate and Tube Burst Probability for EOC-13 7-2 8.0 Updated Probability of Prior Cycle Detection for 19 Inspections in 10 plants 8-1 9.0 References g,y q:\\ ape \\apr98 \\apr90 day. doc
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l Appendix A l
Response to NRC Request for Additional Information on the Last 90-Day Report A-1 l
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FARLEY UNIT-2 1998 VOLTAGE BASED REPAIR CRITERIA 90 DAY REPORT
1.0 INTRODUCTION
This report provides the Farley Unit-2 steam generator tube support plate (TSP) bobbin voltage data summary, together with postulated Steam Line Break (SLB) leak rate and tube burst probability analysis results. These results support continued implementation of the 2.0 volt voltage-based repair criteria for Cycle 13 as outlined in the NRC Generic Letter 95-05 (Reference 9.1). Information required by the Generic Letter is provided in this report including projections of bobbin voltage distributions, leak rates and burst probabilities for Cycle 13 operation. The methodology used in these evaluations is consistent with the NRC SER, Reference 9.2, Westinghouse generic methodology described in Reference 9.3, as well as the methodology reported in the prior ARC reports for Farley Unit-2 (References 9.4 through 9.6).
Eddy current and repair data for TSP indications are provided in Section 3.
=
No tubes were deplugged during the EOC-12 outage with the intention of returning them to service after inspection. The actual EOC-12 voltage distributions as well as leak rates and tube burst probabilities calculated fbr these distributions are compared with the projections for EOC-12 conditions performed using the EOC-11 data.
Leak rates and burst probabilities for the projected EOC-13 voltage distributions are reported in Section 8 and compared with allowable limits.
This report also includes a response to a request for additicnal information from the NRC on leak rate and burst probability analysis carried out after the EOC-11 outage, and it is presented in Appendix A.
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2.0
SUMMARY
AND CONCLUSIONS SLB leak rate and tube burst probability analyses were performed for all three steam generators (SGs) based on their actual measured EOC-12 voltage distributions and the results compared with the projections performed during the last outage as well as a subsequent update for the limiting SG (SG-C). The total number of indications found at TSP intersections in each SG during the current inspection and the actual peak voltages are less than those projected at the beginning of the cycle per the Generic Letter 95-05 requirements using a constant POD of 0.6. With alternate EOC-12 projections based on voltage-dependent POPCD, the total number ofindications is overestimated for SG-A but slightly underestimated for SGs B and C (by about 3%
and 11%, respectively). However, EOC-12 peak voltages are overpredicted for all three SGs with POPCD. The underprediction of the number ofindications occurs for voltages less than 0.7 volts for both POD =0.6 and POPCD. Leakage rates and tube burst probabilities calculated using the actual measured voltages are well below those projected with both a constant POD of 0.6 as well as voltage-dependent POPCD.
SC-C was predicted to be the limiting SG at EOC-12 and was found limiting based on the actual measured EOC-12 voltage data.
For the actual EOC-12 bobbin voltage distribution, the largest SLB leak rate is calculated for SG-C, and its magnitude is 2.4 gpm.
This leak rate value was calculated using an updated ARC database that includes the latest pulled tube leak and burst test data for 7/8" tubes (1996 Farley-2,1997 Farley-1 and 1996 W-2 data) and assuming that leak rate is independent of bobbin voltage. It is substantially less than the current allowable SLB leakage limit of 23.8 gpm. All leak rate values quoted are equivalent volumetric rates at room temperature. The corresponding conditional tube burst probability based on the actual SG-C voltage data is 2.3 x 10 4, and it is well within the NRC reporting guideline of 10 2 The limiting results for EOC-12 projection performed after the EOC-11 inspection were obtained by including unusual phase angle (UOA) indications with potential indications (PIs): projected tube burst probability for SG-C is 2.0x10 3 and the corresponding SLB rate is 9.3
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It is evident that these results substantially exceed those obtained from the gpm.
actual measured voltage data.
SG-C is again predicted to be the limiting SG at EOC-13 conditions since it has more indications than the other two SGs combined and also has more indications over 1 volt returned to service than the other two SGs combined. The EOC-13 leak rate projection was performed using a leak rate versus bobbin voltage correlation. A leak rate correlation can now be applied to 7/8" tubes based on the p-value for the slope of the leak rate correlation on a one-sided basis meeting the Generic Letter 95-05 requirement. Using the NRC mandated constant POD of 0.6 and the latest ARC q:\\ ape \\ apr98 \\ apr90 day. doc 2-1
lb
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l database for 7/8" tubes, the limiting EOC-13 SLB leak rate for SG-C is projected to be 2.0 gpm (room temperature), which is well within the current licensed limit of 23.8 gpm (room temperature). The above limiting EOC-13 leak rate projection is less than the leak rate based on the actual measured EOC-12 voltages (2.4 gpm) because it is obtained uring a leak rate vs. bobbin voltage correlation whereas the latter leak rate was obtained with leak rates independent of voltage. The limiting EOC-13 tube burst probability calculated for SG-C is 6.5x10- 4, and it is more than a decade below the NRC reporting guideline of10 2 A total of 507 indications were found in the EOC-12 inspection, of which 33 are over
- L-2 volts. All indications over 2 volts plus one indication under 2 volts were inspected with a Rotating Pancake Coil (RPC) probe, and only 3 were confirmed as flaws. The largest number of bobbin indications,275 indications, was fbund in SG-C; 23 were inspected by RPC, and none were confirmed as flaws.
No circumferential indications, axial indications extending outside the TSP, PWSCC or volumetric-type signals were identified by RPC inspection at TSP intersections. One axial ODSCC flaw was found by RPC at TSP 2H in tube R30 C78 of SG-B; the bobbin signal for it had a high residual signal and did not identify the flaw. Therefore, RPC inspection
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of support plate residuals was expanded to 66 more intersections in SG-B, but no other ODSCC indication was found. The above tube in SG-B was repaired.
In accordance with a recommendation made in the last 90-day report (Reference 9-4), the UOA call that was applied to indications showing a large phase angle and near 0% depth was not used in the recent (EOC-12) inspection.
Of the 108 indications called as UOAs in the EOC-11 inspection,103 indications were called as PIs, one as Indication not Reportable (INR) and the remaining 4 were not detected during the recent inspection. Nineteen of these indications were RPC inspected in the recent inspection and only one was confirmed. The PIs above 2 volts with prior UOA calls were a major contributor to the low RPC confirmation rate (2 out 33 tested).
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3.0 EOC-12 INSPECTION RESULTS AND VOLTAGE GROWTH RATES 3.1 EOC-12 Inspection Results In accordance with the ARC guidance provided by the NRC generic letter (Reference 9.1), the EOC-12 inspection of the Farley Unit-2 SGs consisted of a complete 100%
bobbin probe full length examination of all TSP intersections in the tube bundles of all three SGs. A 0.720 inch diameter probe was used for all hot and cold leg TSPs where ARC was applied.
Subsequently, RPC examination was performed for all bobbin indications with amplitudes greater than 2 volts in all three SGs. Thirty three indications were found above 2 volts in all SGs combined; they were all inspected with RPC, and only 2 of them were confirmed as flaws and removed from service.
One indication under 2 volts in SG-B was also RPC inspected; it was confirmed, but not repaired in accordance with the 2 volt repair criteria. No tubes were deplugged during the EOC-12 outage with the intention of returning to them to service after inspection.
An augmented RPC inspection was performed consistent with the NRC requirements. All dented intersections with a bobbin voltage greater than 5 volts were inspected with a RPC probe and no indications with a potential ID or OD phase angle were detected. Large bobbin residual artifact signals were also RPC inspected. One axial ODSCC indication not identified by the bobbin inspection was identified with a high residual signal at TSP 2H in tube R30 C78 of SG B This indication had a pancake coil amplitude of 0.71 volts and was repaired. Therefore, RPC inspection of support plate residuals was expanded to 66 more intersections in SG-B, but no other ODSCC indication was found. The above tube in SG-B was repaired. No circumferential indications, axial indications extending outside the TSP or copper-type signals were identified by RPC inspection at TSP intersections.
In accordance with a recommendation made in Reference 9.4, the SG EC guidelines for EOC-12 were modified to call indications with large phase angles and 0% depth (formerly UOAs) as PIs and eliminate the UOA call from the criteria. This change in the guidelines is expected to have increased the number of PI calls. Among the 108 indications called as UOAs in 1996,103 indications were called as PIs in the recent (EOC-12) inspection, one was called as an INR and the remaining 3 indications were not detected. Nineteen of these indications, all 2 volts and over, were inspected with a RPC probe and only one was confirmed as a flaw.
A summary of eddy current (EC) signal voltage distributions for all steam generators is shown on Table 3-1, which tabulates the number of field bobbin indications, the number of these field bobbin indications that were RPC inspected, the number of RPC q:\\apcinpr9M apr90 day. doc 3-1
confirmed indications, and the number of indications removed from service due to tube repairs. The indications that remain active for Cycle 13 operation is the difference between the observed and the ones removed from service. No tubes were deplugged in the current inspection with the intent of returning them to service after inspection.
Overall, the combined data for the Farley Unit-2 steam generators show the following:
A total of 507 bobbin signals were identified as TSP indications during the inspection, and they were all called as PIs.
Of the 507 PIs,217 were above 1 volt and 33 exceeded 2 volts.
A total of 33 indications (all 33 over 2 volts plus under 2 volts) were RPC inspected, of which only three were confirmed.
Of the 10 indications removed from service, only 2 indications exceeding 2 volts were repaired due to ODSCC at TSPs. The rest of the indications are in tubes plugged for degradation mechanisms other than ODSCC at TSPs.
A review of Table 3-1 indicates that more indications (a quantity of 271, with 125 indications above 1.0 volt) will be returned to service in SG-C, more than the combined sum ofindications in the other two SGs, including 21 out of a total of 29 RPC NDD indications over 2 volts returned to service for Cycle 13 operation. Clearly, SG-C will be the limiting SG at EOC-13.
Figure 3-1 shows the actual bobbin voltage distribution for tubes that were in service during Cycle 12, as determined from the EOC-12 EC inspection. Figure 3-2 shows the distribution of the EOC-12 bobbin indications that were repaired and taken out of service, and Figure 3-3 shows the bobbin voltage distribution ofindications returned to service for BOC-13.
The distribution of EOC-12 indications as a function of support plate elevation, summarized in Table 3-2 and illustrated on Figure 3-4, shows the predisposition of ODSCC to occur in the first few hot leg TSPs (270 of the 507 PIs, or about 53%,
occurred in the first four hot leg TSPs), although the mechanism does extend to higher TSPs. Ninety-seven bobbin indications (or about 19%) were reported on the cold-leg side versus about 11% in the 1996 inspection and about 6% in the 1995 inspection. In spite of a slight increase in this percentage, a large majority of the q:\\apc \\apr98 \\apr90 day. doc 3-2
indications at Farley Unit-2 are on the hot leg side, similar to that observed at other plants.
l 3.2 Voltage Growth Rates 1
The technique used for bobbin voltage calibration of transfer standards (cross calibration to reference laboratory standard) during the EOC-11 inspection was slightly different from those applied during the prior ARC inspections at the Farley units. Therefore, EOC-11 voltages were reevaluated using the calibration procedure recommended in Reference 9.7. The calibration procedure fer new bobbin standards recommended in Reference 9.7 calls for performing the mix on the new standard and independently setting the primary and mix amplitudes (for the 20% flat bottom holes) on the reference standard. The voltages for the new standard are then read for the prime frequency and mix frequency. The calibration technique previously used for the EOC-11 transfer standards used voltages setup for the prime frequency with mix voltages obtained using the save/ store software option. The new bobbin standards used during the EOC-11 inspection were recalibrates using the above procedure, and the new calibration factors were used to reevaluate the EOC-11 bobbin signals. The readjusted EOC-11 voltages were used to recalculate growth rates for Cycle 11 and growth for the recently completed Cycle 12. Tables 3-3 and 3-4 respectively show the average growth rate in each Farley Unit-2 SGs during the last two operating periods (Cycles 11 and 12) based on the readjusted EOC-11 voltages. The growth data are presented on an EFPY basis to account for the difference in the length of the two operating periods. The average composite vcitage growth rate from three SGs during Cycle 12 (5.8%/EFPY) is slightly below that for Cycle 11 (6.9%/EFPY). The average EOC-11 growth rate reported originally in Reference 9.4 was 20.2%/EFPY. Thus, the different calibration procedure used during the EOC-11 outage had significantly inflated the growth rate originally established for Cycle 11.
The bobbin voltage growth data for the last two cycles are also shown in Table 3-5 in the form of cumulative probability distribution functions (CPDF), and the same data is presented in a graphical form on Figure 3-5. The data in Figure 3-5 show that growth rates during Cycle 11 are more limiting for the two operating periods. The NRC guidelines require that the more conservative growth distribution for the last two operating periods be applied for projecting the next cycle distributions.
Therefbre, Cycle 11 growth data will be applied to obtain EOC-13 projections.
Table 3-4 also shows average growth rates for each SG during Cycle 12, and Figure 3-6 shows the corresponding cumulative distribution for the growth data. SG-B has a slightly larger average growth as well as the indication with the highest growth (0.7 voluEFPY). Average growth rates observed for all voltages vary between 2.9% and q:\\apc\\ apr98 \\ apr90 day. doc 3-3
8.6%, between SGs, with an overall average of 5.8%, on an effective full power year (EFPY) basis. The average growth for indications with a BOC bobbin voltage above 0.75 volt is 5.1% per EFPY and for indications below 0.75 volt it is 7.9% per EFPY.
Smaller percentage growth observe,d for BOC volts above 0.75 (relative to BOC volts below 0.75) is not consistent with the data for the last inspection, but the above difference in growth rates is not significant. Table 3-6 provides a comparison of average growth data for the last 8 operating cycles, and the data generally show a steady reduction in the average growth rates. The Cycle 11 growth data shown in Table 3-6 is based on reevaluated EOC-11 voltages using the calibration procedure recommended in Reference 9.7, as discussed in the previous paragraphs.
During the EOC-10 outage, many tubes plugged earlier were deplugged and those meeting the current ARC criteria were returned to service. Growth ratea during Cycle 11 for indications in deplugged tubes returned to service at EOC-10 were found significantly higher in comparison to those for active tubes indications. Cycle 12 growth rates for these deplugged tube indications were also calculated separately and compared with those for the active tube indications. Table 3-7 compares growth rates for indications in deplugged tubes and active tubes during two consecutive cycles of operation. It is evident from Table 3-7 that the relatively higher growth rates observed in the first cycle of operation (Cycle 11) for deplugged tube indications were not sustained during the second cycle (Cycle 12). Thus, it appears that deplugged tubes may experience higher growth rates only during the first cycle of operation after return to service. There were only four indications in tubes deplugged at the EOC-11 inspection, so they were not assessed separately.
In the past, some plants with 3/4" tube SGs experience d growth rates that are dependent on the beginning of cycle (BOC) voltage. To de termine if Farley Unit-2 exhibited a similar trend during Cycle 12, growth rate data for Cycle 12 was plotted against BOC voltage, and the resulting plot is shown in Figure 3-7.
The two indications experiencing over 1 volt growth had a BOC voltage under 1 volt, and 7 out of 9 indications with over 0.5 volt growth had a BOC voltage under 1.2 volts. Thus, the Cycle 12 growth data do not show a trend to increase with BOC voltage.
Table 3-8 lists the top 30 indications from the standpoint of growth during Cycle 12, and the data show that the growth rate during Cycle 12 was moderate. Of the 30 indications, only three were confirmed by RPC Inspection. Six on the 9 indications in Table 3-8 identified as being new for Cycle 12 were called as UOAs in the last inspection.
Since the UOA call was eliminated in the EOC-12 inspection and essentially all UOAs from EOC-11 were called as PIs, EOC-11UOAs should be treated as detected indications. Six of the nine indications identified as new in Table 3-8 were called as UOAs in the EOC-11 inspection. Therefore, only three out of the q:\\apc\\apr98 \\apr90 day. doc 3-4
___-______-_-__- - -- - - - - - - - ~
top 30 growth indications in Table 3-8 are truly new indications.
According to the Westinghouse ARC analysis methodology presented in Reference 9.3, the larger of the composite growth rate for all SGs and the SG-specific growth rate should be used in projecting SLB leak rate and tube burst probability for individual SGs. As noted earlier, Cycle 11 growth rates would be used to perform EOC-13 projections as they are slightly higher than the Cycle 12 growth rates. Since the Cycle 11 growth rates for SGs A and B are below the composite growth rate (see Table 3-3), the composite growth rate is applied to those two SGs to provide a conservative basis for predicting EOC-13 conditions. However, predictions for SG-C are obtained using its own growth rate since it is higher than the composite rate.
3.3 Probe Wear Criteria An alternate probe wear criteria discussed in Reference 9.8 was applied during the EOC-12 inspection. When a probe does not pass the 15% wear limit, this alternate criteria requires that all tubes with indications above 75% of the repair limit since the last successful probe wear check be reinspected with a good probe. Accordingly, all tubes containing indications for which the worn probe voltage was above 1.5 volts were inspected with a new probe. An evaluation of worn probe and new probe data :s presented in the following paragraphs.
In accordance with the guidance provided in Reference 9.8, voltages measured with a worn probe and a new probe at the same location were analyzed to ensure that the voltages measured with worn probes are within 75% of the new probe voltages. No new large indications were detected with new probes; thus, worn probes did not miss significant indications. Figure 3-8 shows plots of the worn probe voltages plotted against the new probe voltages for all three SGs. There were only two indications needing retesting in SG-A and only one in SG-B, so the data for those two SGs are combined. The data in Figure 3-8 show a consistent relationship between the two voltages. However, a few indications have the worn probe voltage about a factor of two higher than the new probe voltage.
Composite data from all three SGs are plotted in Figure 3-9. Also shown in Figure 3-9 as a sCid line is a linear regression for the data, dashed lines representing tolerance limits that bound 90% of the population at 95% confidence, and chained lines representing *25% band for the new probe voltages. The mean regression line has about 50o slope indicating that, on the average, worn probe voltages were slightly higher than the new probe voltages. The dotted horizontal line at 1.5 worn probe volts demarcates indications requiring retest from those that do not. The shaded area at the bottom shows the region where a tube requiring repair may be left in service because of probe wear. In the Farley-2 EOC-12 inspection, the e are no occurrences for which a worn probe was less than 1.5 volts and the new probe voltage exceeded the plugging limit, i.e., no pluggable tubes were q:\\apc\\apr98\\apr90 day. doc 3-5
missed due to probe wear considerations.
I Among the indications requiring retesting (worn probe volts > 1.5 volts), six indications fall outside the band formed by the chained lines representing 25% of the new probe voltage, but all data are within the 90%/95% tolerance limit bands. For all the 6 indications outside the 25% band, worn probe voltages are higher than the corresponding new probe voltages, i.e., the worn probe voltages are conservative. No indications lie below the lower 25% band Therefore, data for the six indications outside the 25% band are acceptable.
Overall, it is concluded that the criteria to retest tubes with worn probe voltages above 75% of the repair limit is adequate. The alternate probe wear criteria used in the EOC-12 inspection is consistent with the NRC guidance provided in Reference 9.8.
3.4 Probability of Prior Cycle Detection (POPCD)
The inspection results at EOC-12 permit an evaluation of the probability of detection at the prior EOC-11 inspection. For ARC applications, the important indications are those that could significantly contribute to EOC leakage or burst probability. These significant indications can be expected to be detected by bobbin and confirmed by RPC inspection. Thus, the population ofinterest for ARC POD assessments is the EOC RPC confirmed indications that were detected or not detected at the prior inspection.
The probability of prior cycle detection (POPCD) for the EOC-11 inspection can then be defined as follows.
EOC-11 cycle reported
+ Indications confirmed indications confirmed by and repaired in EOC-11 RPC in EOC-12 inspection inspection POPCD =
(EOC-11)
( Numerator)
+
New indications RPC confirmed in EOC-12 inspection POPCD is evaluated at the 1996 EOC-11 voltage values (from 1998 reevaluation for growth rate) since it is an EOC-11 POPCD assessment. The indications at EOC-11 that were RPC confirmed and plugged are included as it can be expected that these indications would also have been detected and confirmed at EOC-12.
It is also appropriate to include the plugged tubes for ARC applications since POD adjustments to define the BOC distribution are applied prior to reduction of the EOC indication distribution for plugged tubes.
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It should be noted that the above POPCD definition includes all new EOC-12 indications not reported in the EOC-11 inspection. The new indications include EOC-11 indications present at detectable levels but not reported, indications present at EOC-11 below detectable levels and indications that initiated during Cycle 12. Thus, this definition, by including newly initiated indications, differs from the traditional POD de'inition.
Since the newly initiated indications are appropriate for ARC applications, POPCD is an acceptable definition and eliminates the need to adjust the traditional POD for new indications.
The above definition for POPCD would be entirely appropriate if all EOC-11 indications were RPC inspected. Since only a fraction of bobbin indications are generally RPC inspected, POPCD could be distorted by using only the RPC inspected indications. Thus, a more appropriate POPCD estimate can be made by assuming that all bobbin indications not RPC inspected would have been RPC confirmed. This definition is applied only for the 1998 EOC-12 indications not RPC inspected since inclusion of the EOC-11 repaired indications could increase POPCD by including indications on a tube plugged for non-ODSCC causes which could be RPC NDD indications. In addition, the objective of using RPC confirmation for POPCD is to distinguish detection of an indication at EOCna that could contribute to burst at EOCn so that the emphasis is on EOCn RPC confirmation. This POPCD can be obtained by replacing the EOC-12 RPC confirmed by RPC confirmed plus not RPC inspected in the above definition of POPCD. For this report, both POPCD definitions are evaluated for Farley Unit-2. Essentially all of the indications called as UOAs in the 1996 inspection were called as PIs in the 1998 inspection. So, POPCD for the EOC-11 inspection is calculated by treating 1996 UOAs as detected indication.
The POPCD evaluation for the 1996 EOC-11 inspection data is summarized in Table 3-9 and illustrated on Figure 310. Since data for RPC confirmed only indications is sparse, although all confirmed indications were reported at EOC-11, only data for RPC confirmed plus not RPC inspected indications are shown in Figure 3-10. Also shown in the figure is a generic POPCD distribution developed by analyses of 18 inspections in 10 plants and presented in Table 7-4 of Reference 9.7. It is seen from Figure 3-10 that the predicted POPCD values for Farley-2 are equal to or better than the generic POPCD above 0.2 volt. POPCD for Farley-2 remains at or above 0.9 beyond 0.8 volt and reaches unity at about 2 volts.
In summary, the Farley Unit-2 EOC-11 POPCD supports a voltage dependent POD higher than the NRC mandated POD value of 0.6 above about 0.2 volt and approaching unity at about 2 volts. It is concluded that the POD applied for ARC leak and burst projections needs to be upgraded from the constant POD value of 0.6 to a voltage dependent POD.
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3.5 Assessment of RPC Confirmation Rates This section tracks the 1996 EOC-11 indications left in service at BOC-12 relative to RPC inspection results in 1998 at EOC-12. The composite results for all SGs are given in Table 3-10. For 1996 bobbin indications left in service, the indications are tracked relative to 1996 RPC confirmed,1996 RPC NDD,1996 bobbin indications not RPC inspected and 1996 bobbin indications with no indication found in 1998. Also included are new 1998 indications. The table shows, for each category ofindications, the number ofindications RPC inspected and RPC confirmed in 1998 as well as the percentage of RPC confirmed indications.
Six of the 18 RPC NDD indications left in service at BOC-12 were RPC tested during the EOC-12 inspection, and none were confirmed. Therefore, the confirmation rate for 1996 RPC NDD indications 0%.
This result is in consistent with similar evaluations carried out after the 1995 and 1996 outages that showed that none of the 23 prior cycle RPC NDD indications RPC tested confirmed. NRC Generic Letter 95-05 (Reference 9.1), upon NRC approval, allows for consideration of only a fraction of RPC NDD indications from a current inspection in establishing the BOC voltage distribution for the next cycle. A fractional value appropriate for ARC applications is the largest RPC confirmation rate for prior cycle RPC NDD indications found during the last two outages. Thus, based on the data available it would be justifiable to consider < 50% of RPC NDD indications for projecting EOC voltage distributions for Farley Unit-2. However, since NRC approval has not been obtained, leak and burst analyses presented in this report are based on 100% of RPC NDD indications.
3.6 NDE Uncertainties The NDE uncertainties applied for the EOC-12 voltage projections in this report are those given in the prior Farley Unit-2 ARC reports (References 9.4 through 9.6). The probe wear uncertainty has a standard deviation of 7.0 % about a mean of zero and has a cutoff at 15% based on implementation of the probe wear standard.
The analyst variability uncertainty has a standard deviation of 9.3% about a mean of zero with no cutoff. These NDE uncertainty distributions are included in the Monte Carlo analyses used to project the EOC-12 voltage distributions.
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to h
e "E
Na 3456789.3 1 2 3 4 5 6 7.S.9 2 1 2345 l
V V T
67893 1 3 a
0000U00 1
t I
s
_o>2 i
1 1
1 1
I 1 l I 222222222 33 s
T rn m
l 4
H
s S
n T
l t
2 9 8 2 7 3 7 0 5 7 2 3 1
2 1
3 0
o i
R l
a 1
1 4 5 4 4 3 3 2 2 2 2 1
8 1
3 7 2 2 2 5 1
2 1
I 1
2 9 0 9 03 7 9 A c 9
d 2
n 4 2 s
G I
S s
l nd l
o e A
i i 0000 O 1
1 0 02 1
000001 0 2 01 01 0 0 00O 0 0 0 r
ta a c p f
i e 1
8 4 d
o InR 2 e 2
1 t
1 i
e s l
d e
o c
e lc Cm y p y
R ir C
P f
0 0 00 I
0000 0 0 00 00000 I
0 0 0 1
00 00 O00 3 2 2 C m n
g o
g o n
n C i
C r
i u
r D
d u
e e
D c
C tc i
P e 0000 I
0 000 0 0 00 00 0005 7 3 2 3 5 1
2 1
I 1
2 p
4 3 3 e
n R
s c
e I
3 3 3 n
i S
v r
n e e I
gS a
n t
D ui 1
1 4 5 4 43 3 2 2 2 2 1
2 1
1 9
1 5 7 3 2 3 5 1
2 1
I 1
2 0 1
3 2 9 8 2 7 4 8 05 9 3 3 9 03 3 0
7 7 Oes f
3 5 2 o 3b 2
9 uT t
l e
i e
r r h
po S AF 3
9 0 4 3 6 1
4 1
(
1 7 6 1
3 2 2 1
2 I
3 0 1
4 0 1
7 7 7 1
0 01 1
I 00 00 00 5 0 4 1
2 ir e
I 1
1 1
1 4 S t
a l
c 2
1 3
i e n p y
e C
U R r
l b
o a
y f
T ed s
n S
n l
o r a T
l i
a R
l ta 9 0 4 3 6 1
4 3 0 1
4 0 1
5 7 6 1
3 2 2 1
2 1
1 1
1 1
1 1
7 7 7 2 4 2 2 2 5 02 0 0 02 71 2 1
F n A c i
o d
i I
2 1
2 n
tc C ep r s
s o
nd n
t o e I
a i i 0000 0
1 1
0 0 00 0 00 0 000 1
0 1
0 0 r
t a
a r
c p Q0 f
0 00 00 4 2 2
i e o e d
y InR ne r
2 a G1 e d
m e
ml c Cm m
y r
P u e R i 0 00 0 0 0 00 0 0 0 0 00 0 0 0 0 0 0 0 0 00 0 00 0 0 0 0 0 0
a C fn g
o S
t S i C
n ruD de e
Cct ic P e 0 0 00 0 0 00 0 0 000 00 0 0 03 4 3 2 2 5 0 2 00 0 2 p
3 3 3
n R s S
i 2 2 2
n e
-n I
"m 9 0 4 4 7 1
4 3 01 4 0 1
5 7 7 6 1
3 2 2 1
2 1
1 1
1 I
1 1
7 7 7 3 4 3 2 2 5 02 1
0 02 7 2 d
8 3
I 2
1 2
3 4 5 6 7 8 9 1
1 2 3 4 5 67 8
- 9. 2 1
2 3 4 5 6 7 8
- 9. 3 1
3 t
I 2
la V v 00 0 0 00 0 1
1 1
1 1
1 1
1 1
2 2 2 2 2 2 2 2 2 3 3 oT > >
l
Table 3 2 Farley Unit 2 April 1998 TSP ODSCC Indication Distributions for Tubes in Service During Cycle 12 i
Tube Steant Generator A Steam Generator 11 Support Plate Number of 31stimum Ascrage 1,argest Average Number of Stasimum Ascrage Largest Ascrage Indications Voltage Voltage Growth Growth Indications Voltage Voltage Growth Growth Olli 27 1.61 0 83 0.39 0 03 29 1.53 0 80 0 88 0.12 O211 20 2.10 0.87 0.54 0 05 23 2 88 0.79 0.37 0.11 0311 1
0 66 0 66
-0.02
-0.02 10 1.94 1.31 0.45 0 16 N11 1
0.65 0 65 0.02 0 02 2
0 78 0.67 0.09 0 00 05l1 8
2.44 1.23 0.19 0.07 13 1.72 1.14 0.18 0 03 0611 8
2.12 1.23 0.15 0 04 8
2.92 1.26 0 30 0.09 0711 5
1.48 1.11 0.09
-0 04 23 1.92 0.77 1.16 0.08 07C 0
28 1.73 0 93 0.22 0 05 06C 1
0 49 0.49 0.13 0.13 7
3 07 1.69 0 58 0.19 OSC 7
1.30 0 85 0.09 0.03 4
1.34 1.12 0.29 0 08
~
04C 0
0 03C 2
0 64 0 56 0.02
-0(N 2
2.65 1.94 0.17 0.13 02C 1
0.51 0 51 0 01 0.01 2
1.05 0.93 0.35 0.18 01C 0
0 Total 81 151 Tube Steant Generator C Composite of All SGs Support Plate Number of 51asimum Ascrage I.argest Ascrage Number of 31aximum As erage I,argest Ascrage Indications Voltage Voltage Growth Growth Indications Voltage Voltage Grow th Grow th 0111 102 1.98 0.96 0.65 0.06 158 1.98 0.91 0 88 0.07
()2l1 33 2.02 0.85 0.41 0 06 76 2 88 0 84 0.54 0.07 0311 12 2.55 0 80 0.15 0.01 23 2.55 1.02 0.45 0.07 0411 10 1.89 0 85 0.21 0 00 13 1.89 0.81 0.21 0.00 0511
- 0 2.73 1.44 0 33 0.04 41 2.73 1.30 0 33 0.04 06l1 32 3 28 1.42 0.36 0 07 48 3 28 1.36 0 36 0 07 0711 23 2.21 1.16 0.46 0.05 51 2 21 0 98 1.16 0 06 07C 13 1.66 1.14 1.02 0.13 41 1.73 1.00 1.02 0.07 06C 10 2 ho I.65 0.24 0.14 18 3.07 1.60 0 58 0,16 05C 13 3.26 1.57 0 33 0.16 24 3 26 1.29 0.33 0.11 04C l
0.91 0 91 0.03 0.03 1
0 91 0.91 0 03 0 03 03C l
0 61 0 61 0 00 0 00 5
2 65 1.12 0 17 0 02 02C 2
- 2. l l 1.52 0.24 0 17 5
2.11 1.08 0 35 0.14 Olc 3
0 80 0 63 0 09 0 03 3
0 80 0 63 0 09 0 03 Total 275 507 o,.
o.m.. -,, ~
3-11
Y P
FE 9 4 5 9 4 2 0 9 6 8 5 9 r
6 28 4 4 5 2 0 2 01 3 12 e
P s
ecne le r
c e
y f
C e
0 1
2 4 8 8 7 2 A 1
5 9 f
i D
i 9 3 1
6 5 6 2
I 3
1 4
1 r
1 4
6 t
n n
o E
i a
t t
a a
r D
b r
i o
la Y
t C
P a
I 3 3 6 5 9 8 91 M g e e E
n 0
1 6
2 3 5 r
F e
6 0
A 4 2 6 B
1 0 0 eI 0 2 C
0 0
0 al b 1
r 0 0 0 r
r 1
0 I.
t c
r e
0 0 0 o 0 0 0 o 0 0 0 o 0 0 0 o
e G
t t
t u y r
P a
a a
OCP m
r r
r 6 g r a
e e
e 9 n o e
n n
n i f e
e e
t 9 r le S
t c
l G
G G
1 u n y
l m5 0 5 6 8 rD u C
A 3 7 8 m2 1
0 3 m0 5 5 8
1 3
5 3 8 3 e 4 2 1
- bh o f
a a 0 0 0 a
e o
0 0 1
e 0 0 0 0 0~0 e
1 0 2 c
e 3 mt c i
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0 0 0 t
0 0 0 0 0 0 t
w S
S S
t t
e e A
n is t
v o E
lb r o o
o eT N Gt p
d m
- e e
e gt g
o 2 a s a
C t
t u
t l
i l
n oj o
d V
C 2 3 4 5 2 6 0 0 3 9 6 7 UV a O
9 5 2 8 5 2 8 5 1
9 5 2 e
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B 0 0 1
0 0 1
0 0 1
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a c
a r
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r r e e
)
a e g v
Y F v a
A P
E At l L
o 6
V 0
f s
4 1
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8 2 7 2 7 3 3 1
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fo o
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ra sa g s g
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g s g s u
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n B
a lt t
a lolt a
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a lolt d ol ol I
RV o RV o RV o RV oi e
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V V
V Vle a
g e
5 e
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5 5
5 c
g 5
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g 5
g 5
y V R lt 7 7 lt 7 7 l
< 2 lo < 2 o n
a a
a a
l a
t 7
t o
7 t
7 7 C n
o < 2 o < 2 o
V c V r V c V c d
e o e m e o e o w
r s
r p
r r
s a
i V i V i V i V t
t t
t H
n n
n n
E E
E E
YPF E
8 9 1
9 1
2 6 6 t
r 1
3 2 4 6 h
5 7 5 2 2 3 8 i 7 5 7 4 w
e P
o r
G tnec le r
c e
y P
C e
3 9 4 7 7 0 8 7 2 5 3 8 ir 7
9 6 3 2 4 0 4 t
1 1
9 6 9 5 n
E a
taD r
h o
Y t
t w
P a
6_2 6 6
2 o
F e
5 M6 A 2
1 3
B 7 61 _9 9
5 r
1 4 O 3 8
C 5 M6 r
E n
0 0
r 0 0 0 r 0 0 0 r
0 1 0
(
1 G
e 0
0.
0 o 0 0 0 o 0 0 0 o
0 0 0 r
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t t
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y a
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a e
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t tu o
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n n
g V
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e On lc l
S 8 r g
y l
G G
G e
i 9 u a
C A
0 3 4 m2 1
5 9 7 1
a 4 0 m5 6 2 m8 0 9 7
3 8
3 r
f a
a 6 5 7 9
D e
e o
0 0 0 0 0 0 r
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e 0 0 0 1
4 v
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0 0 0 0 0 0 t
0 0 0 t
0 0 0 h
A n
t t
t e pw E
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S S
l i
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lb A p
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in a o
Ul V
C 6 3 1
9 3 2 8 2 3 3 4 7 t
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O 9
5 3 8 5 2 8 5 2 0 5 3 yV g
B 0
0 1
0 0 1
0 0 1
1 0
1 e
a e
r lr g
e a
a v
F r A
ev
)
Y A
P f
s tL o
n r
o 62 e
it 7
4 3 b
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2 8 1
9 2 1
5 6 5 lo5 t
5 i
1 7 7 7
6 t
8 3 4 m
c 5
2 2 D
2 I
1 P
u d
N I
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l 2
064 fo no i
e e
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tar g s g s g
t t
n s
d s
g s u
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s n
s n
s e
e a lolt a
lt t
a lol a
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2 g
ol ol a
g RV o R V RV o o
n V
V V
RV o 1
t V
5 5
5 le l
e 5
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a g
5 g
c 5
g 5
g 5
y V R t
7 7
7 a 7 o
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7 a
7 ta 7
a 7
C t
l
< 2 l
< 2 lo < 2 l
< 2 on o
V r V c V c V c d
r e
e o e
e o e o e
i s r
s s
r s
r s
a t
V i V i V i V 1
n t
t t
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n n
E E
E E
v y
C i
t s
a 6
1 2
l
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3 2 2 9 4 1
I 0
I 1
0 0 0 0 0 0 7 0 7
n 3
7 3 u
1 2
i 5
muC 1
F 1
7 9 9 9 6 3 4 4 4 I
1 I
3 8 3 8 e
D 0 2 I
7 7 7 3 5 6 7 8 8 8 8 9 9 0 2
9 c
P 0 0 I. 4 7 8 9 9 9 9 9 9 9 9 9 9 9 9 1
l y
C 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 C
FD MM3 7 6 3 5 9 3
%0 6
7 2 5 1
7 8 9 9
X X P
(
(
0 3 7 9 9 9 9 9 9 9 C
C 0 0 0 0 0 0 0 0 00 0 0 1
is 2
1 s
r e
a l
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C s
8 e
9 0 5
P
'd 1
0 I
7 1
3 7
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4 1
4 1
1 0 0 1
0 0 0 0 0 0 7
F e
1 i
2 E
G n
m a
a 1
n e
F t
1 8 o S
9 9 4 5 8 5 2 7 4 7 6 6 8
3 7 6 l
c P
0 0 1
4 6 8 8 8 9 9 9 9 9 9 9 9 9 9 1
9 2 l
D 0 3 3 3 9 1
7 9 2 4 5 6 6 7
8 8 9 0 e
7 i 1 y
C 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 r
e C
pl 5 Ac
-3 y
2C F
b n P
0 01 0 2 7 8 9 9 9 9 9 9 9 I
let r 3
6 8 9 4 7 4 7 7 3 3 3 D
0 8 5 0 7 4 7 8 8 9 9 9 0 i
o F
2 aU C
0 0 0 0 0 0 0 0 0 0 0 0 T
s B
1 yc r
e ei o
c l
l t
t r s a
y I
ai r
C
" s t
F a e
d I
6 8 5 I
4 2 O 1
0 0 1
0 2 0
0 0 0 0 5
t n
n I
2 6 2 1
I S
e I
1 G
h t
w ma o
e 1
r t
1 F
G S
9 8 8 2 4 2 1
1 1
I 1
0 e
D 0
1 2 M5 8
9 9 9 9 9
l lc P
0 0 I.
9 9 9 9 9 9 9
a y
C 0 0 0 O 0 0 0 0 0 0 0
1 n
C ig S
F 2
D 0
1 6 5 1
5 8 4
8 9 5 7 8 0 P
0 0 0 3 8 9 9 9 2
0 0 0 1
A C
0 0 0 0 1
r e
o lc t
a y
r C
s e
'd 5 6 0
1 6
9 2 I
1 0 0 0 0 O 0 0 0 0 0 1
n
" n 2 3 8
e I
G m
a 1
e F
t 1
e D
0 1
5 71 7 41 7 6 6 6 6 4 7 S
5 5 8 8 8 8 0 lc P
0 0 0 3 7 9 9 9 9 9 9 y
C 0 0 0 0 0 0 0 0 0 0 1
C ta t
l s
le l
3 2 1
1 2 3 4 5 6 7 8 9 I
2 3 4 5 ta o
0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 1
1 3
o DV T
l l
l l
Table 3-6 i
Farley Unit 2 April 1998 Average Voltage Growthilistory Composite of All Steam Generator Data Bobbin Voltage Nurnber of Average Voltage Aserage Voltage Growth Ascrage Percentage Growth Range Indications BOC Entire Cycle Per EFPY Entire Cycle Per EFPY Cycle 12 (1996 1998) 460.2 EFPD Entire Voltage Range 507 0.96 0.070 0.056 7.3%
5.89 V we <.75 Volts 224 0.53 0.053 0.042 9.99 7.9%
2.75 Volts 283 1.31 0.084 0.066 6.49 5.19 Cycle 11 (1995 1996) 477 EFPD Entire Voltage Range 411 0 92 0.083 0.063 9.09 6.9%
V wr <.75 Volts 187 0.53 0.017 0 013 3.1 %
2.49 2.75 Volts 224 1.24 0.138 0.106 11.2 9 8.5%
Cycle 10 (1993 1995) - 438 EFPD Entire Voltage Rance 197 0.79 0 010 0.008 1.29 1.09 V me <.75 Volts 122 0.55 0.02 0.017 3.6%
3.09 2.75 Volts 75 1.18
-0.007
-0.006
-0.6%
-0.59 Cycle 9 (1992 1993) 462 EFPD Entire Voltage Range 169 0.76 0.090 0.071 11.89 9.49 V me <.75 Volts 105 0.51 0.10 0.079 19.69 15.5 9 2.75 Volts 64
- 1. I8 0.090 0.071 7#4 6.0%
Cycle 8 (1990 - 1992) 405 EFPD Enure Voltage Range 308 0.73 0.140 0.126 19.2<7<.
17.3 %
V wr <.75 Volts 233 0.57 0.17 0.153 29.89 2699 2.75 Volts 75 1.23 0.040 0.036 3.3%
2.9%
Cycle 7 (19N9 1990) 468 EFPD Entire Voltage Range 326 0.71 0.110 0.086 15.5 9 12.1%
V c <.75 Volts 207 0.52 0.16 0.125 30.8%
2409 2.75 Volts 119 1.04
-0 120
-0 094
- 1 1.5 %
-9 0%
Cycle 6 (1987 - 19N9) 416 EFPD I
Entire Voltage Range 316 l
0.59 l
0.200 l
0.176 l
33 99 l
2989 Cycle 5 (1986 - 1987) 460 EFPD Entire Voltage Range 291 l
0.55 l
0.130 l
0.103 l
23.6'7r l
1889 3-15
<... --co m :m
y rl 0 0 0 0 0 0 0 0 0 0 0 0 C Go
.V se gl b
v u
A Ts d e e c gn ge n
r u e 2 o t
lpf t
n i
f 1
i eD a
0 1 8 5 9 7
D Cc u 1 0 1 7
8 5 1 5 1 7 2 0
6 2 8 1
1 2 5 7
n Oio 2 4 5
d o E dC ni at n
a I
e r vbi it l
c a A C Y
r rof P
o f
F]
sd e e EY
/P t
1 lcs 1
8 yu hF 8 6 8 2 9 4 0 7 0 7 9 6 6 5 6 2 5 6 6 9 2 9 9 1 9Cj et E d
1 4 1 1 9 0 0 w/
2 6 4 4 6 l
9 v e yot
. 0 0 0 0 0 0 2 1 0 2 0 e a c
s 0
1 i iR rl 0 0 0 0 0 0 0 0 0 0 0 0 l
t C Go rpu s 7
c e
.V Aeg gI
-3 s a v
le2 nt A
t olo bia nC V TU 2 1
g1 yn leiC uO n
r r
F D E 1 o*
a 1 it eg t
n 8
9 3 2 0 1 1 n
Ca u 4 2 7 9 1 0 9
t c
0 1 0 4 3 0 1 1 ai 8
R Oio s
1 1
1 2 3 1 4 U
h E d C s
n twi I
s oa r B G Y eP gF ar E e n vAan 0
0 0
0 f
1 1
1 1
oo 0
0 0 -
0 e
C C
C C
nh 1
1 1
1 ot p
io T
leOd eOd eOd eOd w
y E n c i yd in c i
e e
e e
E n c E s
E n l
l l
cyd bi ydb b yd b r
r apG e
C e C e mC e
C e g m g
g m g m b
e g o e g o e g o e m
g o u
v v
v v
uCi uCi uCi uC d o
i C
T t
l t
l t
l t
l e
c p c p c p c p d
A e A e A e A e u
D D
D D
l cn I
TO N
s l
la s
C G
G A
A B
C S
O S
l U
l A
Table 3-8 Fariey Unit 2 April 1998
{
l Summary of Largest Voltage Growth Rates for BOC-12 to EOC-12 l
Steam Generator Bobbin Voltage RPC New SG Row Col Elevation EOC BOC Growth Confirmed ?
Indication ?
B 3
72 07H 1.92 0.76 1.16 N
N C
5 57 07C 1.43 0.41 1.02 N
N B
1 6
OlH 1.38 0.5 0.88 N
Y C
31 69 OlH 1.5 0.85 0.65 N
N B
13 84 07H 1.52 0.92 0.6 N
N B
11 2
06C 1.76 1.18 0.58 N
N A
37 52 02H 2.1 1.56 0.54 Y
N C
22 84 OlH 1.74 1.22 0.52 N
Y B
4 87 06C 3.07 2.57 0.5 Y
Y B
2 42 01H 1.08 0.61 0.47 N
N C
37 65 OlH 1.67 1.2 0.47 N
N C
19 21 07H 0.93 0.47 0.46 N
N B
14 91 03H 1.94 1.49 0.45 N
N C
15 56 02H 1.53 1.12 0.41 N
Y B
23 77 03H 1.77 1.37 0.4 N
Y C
32 65 OlH 1,77 1.37 0.4 N
N A
12 91 OlH 1.32 0.93 0.39 N
N B
4 69 02H 2.88 2.51 0.37 Y
N C
35 70 OlH 1.81 1.44 0 37 N
N C
33 55 06H 1.36 1
0.36 N
Y B
7 72 02C 0.81 0.46 0.35 N
Y C
24 74 OlH 1.97 1.63 0.34 N
N C
38 58 06H 1.86 1.52 0.34 N
N C
3 12 07H 0.79 0.45 0.34 N
Y C
3 68 05C 2
1.67 0.33 N
Y C
30 67 OlH 1.98 1.65 0.33 N
N C
36 61 OlH 1.59 1.26 0.33 N
N C
28 77 05H 1.44 1.11 0.33 N
N B
11 70 02H 1.57 1.25 0.32 N
N B
19 71 03H 1.54 1.22 0.32 N
N omm si, t. des 7nns o ss ru 3-17
d d
3 0 8 5 0 3 2 1
t eoe 1
1 CmNt c
r Pi s e f
Rnup i s oP n C
I 4 8 9 1
0 7 0 0 0 c
4 7 9 3 0 2 0 0 0 a -
8 8 8 9 9 9 0 0 0 r
D F
0 0 0 0 0 0 1
1 1
C n
P o
O o
i P
tce 0
1 t
t n 0 0 0 1
0 0 4 2 1
9 e
u
/ / /
/ / / / / / /
D o
d e
e C 0 0 0 0 0 0 4 0 1
9 2
1 Cm lc r
y Pi f
C Rn o r
C o
0 0 0 0 0 c
0 0 0 0 0 ir a -
0 0 0 0 0 a
r Pt F
f a 0
1 1
1 1
oD y r i o n
d t
nd e
l t
io n ioe g
a i
ib r cb 6t m g
9 c 9 ef lu 9
1 a e eb ir 0 0 0 0 0 0 3 9 0 3
b n po pn P
1 1
1 o e sB s o d rG n
n 8 P I
iC na 3 r m o a ef e
l n
d d
b nt a oS o
et e
o 8iCmn t
t Til 9
1 8
c c
r 8
9 4 5
5 t
l epi s e
0 0
5 aA 9
0 1
0 0 2 n lu p
3 8 5 3
pRf 3
u 1
1 1
4 f
s s
op n
l a o "h
i C
I n
v e Et i s 2
I o
b6 1
p n
d og o
e
-Cm Bg 8tcC m
i Oo 8
eP ir 9
0 0 0 0 0 0 1
1 0 0 E C 9
1 1
f pR n
1 s
o 89 In C
9 1
2 n
d d
t o
et e
i o
n 8iCmn t
t s
c c
U 9
r 4
0 2
0 epi s e
0 7 4
3 0 0 0 3
n 9
o pRfnu p
1 1
1 5
y i
1 l
s s
op n
e t
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4.0 DATA BASE APPLIED FOR ARC CORRELATIONS Correlations have been developed for the evaluation of ODSCC indications at TSP locations in steam generators which relate bo%n voltage amplitudes, free span burst pressure, probability of leakage and associated leak rates.
The Westinghouse methodology used in the calculation of these parameters, documented in References 9.3 through 9.6, is consistent with NRC criteria and guidelines of References 9.1 and 9.2.
The slatabase used for the ARC correlations that are applied in the analyses of this report are consistent with the NRC SER applicable to the Farley Unit-2 EOC-12 inspection. EOC-12 projections reported originally in Reference 9.4 utilized the data base documented in Reference 9.9.
When additional data became available from Plant A-1 in 1997, it was determined that it had a non-conservative effect on the database. Therefore, EOC-12 projections for the limiting SG (which is SG-C) was repeated using an updated database that included data from the 1996 Plant A-2, 1997 Plant A-1 and 1996 Plant W-2 pulled examinations. This updated database and the ARC correlations based on it are presented in Reference 9.10. To compare leak rate and burst probability results based on the actual measured voltage data with the projections, analysis using the actual voltages were carried using both sets of databases used in the EOC-12 projections.
The latest database for 7/8" tubes which includes data from the 1996 Plant A-2,1997 Plant A-1 and 1996 Plant W-2 pulled examinations was used to perform leak rate and burst probability projections for the ongoing cycle. A leak rate correlation can now be applied to 7/8" tubes based on the p-value for the slope of the leak rate correlation on a one-sided basis meeting the Generic Letter 95-05 requirement. The latest ARC correlations have been issued as Addendum-2 to the EPRI database report (Reference 9.7). This addendum was issued subsequent to the Farley Unit-2 EOC-12 inspection.
NRC concurrence for the use of these correlations has not been obtained at the time 1
of this report. Since the correlations in Reference 9.7 yields higher leak rate than
}
those in Reference 9.10, EOC-13 projections were calculated using both sets of
]
correlations. The following leak rate correlation is developed in Reference 9.7 for 7/8" tubes.
f T
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Leak Rate (l/hr) 10s
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The above leak rate correlation was used to perform EOC-13 SLB leak rate projections for the limiting SG.
The leak rate data in the database represent room measurement of leakage at q:\\apc\\apr98\\apr90 day. doc 4-1 L
prototypic SLB conditions (i.e., leakage at SLB conditions cras condensed and measured at room temperature). Therefore, SLB leak rate calculated using the ARC correlations provides a volumetric rate at room temperature.
. For the SLB leak rate correlation, the NRC recommends that Model Boiler specimen 542-4 and Plant J-1 pulled tube R8C74, TSP 1 be included in the database. This database is referred to as the NRC database and the correlations for probability of leakage and leak rate as a function of bobbin voltage presented in both References 9.7 and 9.10 included those datapoints.
The upper voltage repair limit applied at the EOC-12 inspection was developed from the ARC database of Reference 9.10, which was the database available two months prior to the inspection.
The structural limit is 8.3 volts. The allowance for voltage growth is 30%/EFPY, which bounds the Farley Unit-2 data and is the minimum growth allowance required by Generic Letter 95-05 (Reference 9.1). For the expected 1.24 EFPY fbr Cycle 13, the growth allowance becomes 37.2%. The allowance for NDE uncertainty is 20% per Generic Letter 95-05. The upper voltage repair limit is then 8.3 volts /1.512 = 5.28 volts.
1
! e q:\\ ape \\apr98\\apr90 day. doc 4-2
5.0 SLB ANALYSIS METHODS Monte Carlo analyses are used to predict the EOC-13 voltage distributions and to calculate the SLB leak rates and tube burst probabilities for both the actual EOC-12 voltage distribution and the predicted EOC-13 voltage distribution. These methods are consistent with the requirements of the Farley Unit-2 NRC SER (Reference 9.2) and are described in the generic methods report of WCAP-14277, Revision 1 (Reference 9.3) and the prior reports for Farley Unit-2 (References 9.4 through 9.6),
and are in accord with NRC Generic Letter 95-05 (Reference 9.1).
Leak rates calculated with the WCAP-14277 methodology provide a volumetric leak rate at room temperature and they are compared with allowable volumetric leak rate at room temperature.
The leak rate database for 7/8" tubes does not satisfy the requirement for a SLB leak rate versus bobbin voltage correlation (p-value for the correlation slope parameter calculated on a two-sided basis less than 5%) used at the time of last (EOC-11) inspection. Therefore, leak rate projections for the EOC-12 condition were carried out using a distribution ofleak rate data independent of voltage. The analysis methods for applying this leak rate model are given in Section 4.6 of WCAP-14277 (Reference 9.3).
A Monte Carlo analysis is applied to account for parameter uncertainties although the leak rate is independent of voltage. This method ofleak rate analysis is similar to that of draft NUREG-1477 except for the uncertainty treatment. Leak rate analyses based on the actual measured voltage data were also performed using a leak rate correlation independent of voltage.
As mentioned in the previous section, a leak rate correlation can now be applied for 7/8" tubes based on the p-value for the slope of the leak rate correlation calculated on a one-sided basis meeting the Generic Letter 95-05 requirement. Therefore, leak rate analysis for the EOC-13 condition was carried out using the leak rate vs. bobbin correlation shown in the previous section.
l q:\\apc\\apr98 \\apr90 day. doc 5-1 l
l 1
i 6.0 BOBBIN VOLTAGE DISTRIBUTIONS This section describes prediction of the EOC voltage distribution used for evaluating tube leak and burst probabilities at the end of the operating period. The calculation consists of establishing the initial conditions (i.e., the bobbin indication population distribution) based on eddy current inspection data and projecting the indication growth over the operating period. Since indication growth is considered proportional
)
to operating time, the limiting tube conditions occur at the end of any given time period or cycle.
The bobbin vcltage distribution established for the BOC conditions is adjusted for I
measurement uncertainty using a quantity termed probability of detection, as described in the following paragraphs. Other input used for predicting the EOC voltage distribution and the results are presented below.
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6,1 Probability of Detection The number of bobbin indications used to predict tube leak rate and burst probability is obtained by adjusting the number of reported indications to account for measurement uncertainty and confidence level in voltage correlations.
This is accomplished by using a POD factor. Adjustments are also made for indications either removed from or returned to service. The calculation of projected bobbin voltage frequency distribution is based on a net total number ofindications returned to service, defined as:
Ni NToiars = ND - Naep.,e4 + Noepios,ca.
where:
NrotnTs = Number of bobbin indications being returnnd to service for the next cycle.
Ni = Number of bobbin indications (in tubes in service during the previous cycle) reported in the current inspection.
POD = Probability of Detection.
Nrepaired = Number of Ni which are repaired (plugged) after the last cycle.
Ndeplugged = Number of previously-plugged indications which are deplugged after the last cycle and are returned to service.
i There were no deplugged tubes returned to service in the recent inspection.
The NRC generic letter (Reference 9.1) requires the application of a constant POD =
q:\\apc\\apr98\\ apr90 day. doc 6-1
0.6 to define the BOC distribution for the EOC voltage projections, unless an alternate POD is approved by the NRC.
6,2. Cycle Operating Time The following operating period values are used in the voltage projection calculations:
' Cycle 11 = 477 EFPD Cycle 12 = 460.2 EFPD Cycle 13 = 452.9 EFPD (estimated) 6.3 Calculation of Voltage Distributions Bobbin voltage projections start with a cycle initial voltage distribution which is projected to the corresponding cycle final voltage distribution, based on the growth rate adjusted for the anticipated cycle operating time period. The overall growth rates for each of the Farley Unit-2 steam generators during the last two operating periods, as represented by their CPDFs, are shown on Table 3-5. A Generic Letter 95-05 requirement is that limiting growth rate for the past two cycles of operation should be used in the projections. The 1995 - 1996 operation (Cycle 11) growth rates slightly exceed those of the 1996 - 1998 (Cycle 12) operation and are used to predict the EOC-13 bobbin voltage distributions. Further conservatism for the EOC-13 bobbin voltage prediction is provided by the use of the larger of the composite growth rate for all SGs and the. SG-specific growth rate in projecting EOC voltages for each SG.
The methodology used in the calculations of EOC bobbin voltage distributions is described in Reference 9.3.-
For each SG, the initial bobbin voltage distribution ofindications being returned to service for the next cycle (BOC-13) is derived from the actual EOC-12 inspection results adjusted for tubes that are taken out of service by plugging. The Cycle 13 bobbin voltage population data is summarized on Table 6-1. It shows EOC-12 bobbin
- voltage indications, the subsequent plugged indications (which were in service for Cycle 12 and then taken out of service, albeit not all for reasons of ODSCC at TSP),
and the BOC-13 indications corresponding to a constant POD value of 0.6 as well as the voltage dependent generic POPCD. The POPCD distribution used is shown in Figure 6-1.
6.4 Predicted EOC-13 Voltage Distributions The licensing-basis calculation fbr the predicted EOC-13 bobbin voltage distributions is performed for all SGs with a constant POD value of 0.6 in accordance with a NRC requirement.
.In addition, calculations were also performed using a voltage q:\\ ape \\apr98\\apr90 day. doc 6-2
dependent generic POPCD distribution developed based on bobbin and RPC data from 18 EC inspections at 10 different plants. Development of a generic POPCD distribution is described in Reference 9.7.
An updated POPCD distribution that includes the latest Farley Unit-2 inspection (EOC-12) data is shown in Section 9, but was not used in the present analysis.
The Farley Unit-2 steam generators BOC-13 voltage distributions used to predict the EOC-13 voltages are shown in Table 6-1.
As mentioned earlier, the EOC-11 composite growth rate data shown in Table 3-5 were applied to SGs A and B (since their own growth rates are smaller than the composite growth rate) and its own growth rate distribution was used for SG-C (since it is higher than the composite growth rate). This approach is recommended in Reference 9.3. Growth data were represented by a histogram.
Table 6-2 provides the EOC-13 voltage distributions predicted using the BOC-13 voltage distribution shown in Table 6-1.
As anticipated, the largest number of indications is predicted for SG-C, 454 indications for a constant POD of 0.6.
The assumed BOC-13 and predicted EOC-13 bobbin voltage frequency distributions for all three SGs are also graphically illustrated on Figures 6-2 to 6-4. The largest bobbin voltage predicted for EOC-13 is in SG-C, and its magnitude is 5.7 volts for a constant POD of 0.6 65 Comparison of Predicted and Actual EOC-12 Voltage Distributions I
The actual EOC-12 bobbin voltage distributions and the corresponding predictions presented in the last 90-day report (for EOC-12 inspection, Reference 9.4), are compared in Table 6-3 and on Figures 6-5 and 6-6. SG-C was predicted to be limiting for EOC-12 which is consistent with the actual measurement since this SG has the highest number ofindications as well as the largest indication found in the EOC-12 inspection. The total number of indications for all SGs is overpredicted by 20% to 26% in the licensing-basis analysis with a POD of 0.6.
Also, the licensing-basis l
analysis significantly overpredicted the actual EOC-12 bobbin voltage population over j
1 volt as well as the population above 2 volts in all three SGs. The overprediction for l
l indications in virtually every voltage size range demonstrates conservatism in the projection methodology.
EOC-12 voltage distributions based on the voltage-I dependent POPCD also yields conservative results.
While the total indication population for SGs B and C are under predicted by a small amount (3% to 11%), the indication population over 1 volt as well as the population above 2 volts are overpredicted for all three SGs. Since it is the indication population over 1 volt that dominates the predicted leak rate and burst probability, it is concluded the voltage-l q:\\apc\\apr98\\apr90 day. doc l
6-3
dependent POPCD yields conservative results.
q:\\ apc \\apr98 \\ apr90 day. doc G-4
2 5 8 8 7 9 0 7 7
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l 0 3 8 8 5 4 4 1
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b I
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7 5 9
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1 0 0 0 2 5 t
5 6 4 6 3 2
. 0 0 0
1 0
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3
. 7 4I 4 4 7 4 3 2 0 0 0
l1 0 0 n0 0 0 0 0 0 0 5 2 7 2
1 p
2 31 O
B 3
1 C
O C
A B
, 3 7 0
7 3
D 7 7 7
7 7 3 7 7
0 3 0 0 0 3 7 7
O r
Oe 6 6 33 6 6
6 0 6 6 3 6 6 6 0 3 0 0 0 36 t
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1 6
1 6
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6 5 3 0 0 0 2 1
0 0 6 0 0 0 0 0 0 0 2 E
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~ i 0 0 O 0_ 0 0 0 0 O I
0 0 0 0 0 0 0 01 0 0 0 I
0 0 0 0 0 0 0 3 1
m
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1 2
ke 0 0 0 0 0 0 0 1
34 5 6 7 8 9 I. 2 3 4 5 6 7 8 9 1
3 1
3 2 2 2 2 2 2 2 2 2 3 3 V
Tcbla 6-2 Farley Unit 2 April 1998 j
Voltage Distribution Projection for EOC - 13 Combined Data for Hot and Cold Leg indications l
Steam Generator A l
Steam Generator B l
Steam Generator C Voltage Projected Numberof mdications at EOC 13 f
POPCD POPCD POPCD 6
6 6
0.2 0.07 0.09 0.28 0.37 0.49 0.64 1
0.3 0.99 1.20 3.18 3.97 4.54 5.79 0.4 4.48 4.77 8.6R 9.69 _
8.58 166 0.5 10.19 9.98 14.oS 14.99 17.84 17.46 06 13.21 12.19 18.73 17.42 27.43 24.85 0.7 13.03 11.36 20.61
'7.80 32.17 27.51 0.8 11.41 9.45 21.47 17.42 32.68 26.53 0.9 9.57 7.59 20.57 16.03 31.62 24.72 1.0 7.88 6.03 18.48 13.93 29.53 22.30 1.1 6.85 5.09 16.63 12.19 27.13 20.08 1.2 6.60 4.72 15.22 10.88 24.82 18.06 l
1.3 6.89 4.82 13.63 9.57 22.86 16.38 j
1.4 7,11 4.91 11.73 8.14 21.40 15.05 i
1.5 6.78 4.64 9.84 6.77 20.23 14.02 1.6 5.83 3.06 8.28 5.63 18.92 12.91 l
1.7 4.60 3.11 7.14 4.79 17.36 11.74 I
1.8 3.42 2.30 6.22 4.14 15.70 ~
10.55 1.9 2.53 1.69 5.36 3.55 13.89 9.27 2.0 1.95 1.29 4.52 2.99 12.20 8.11 2.1 1.58 1.02 3.72 2.45 10.68 7.09 2.2 1.34 0.85 3,01 2.00 9.30 6.16 2.3 1.17 0.72 2.40 1.60 8.12 5.34 2.4 0.97 0.59 1.92 1.28 7.15 4.70 j
2.5 0.77 0.44 1.57 1.03 6.22 4.05 1
2.6 0.59 0.33 1.34 0.88 5.33 3.44
{
2.7 0.44 0.24 1.20 0.78 4.51 2.89 2.8 0.34 0.01 1.09 0.70 3.81 2.44 i
2.9 0.26 0.00 1.01 0.64 3.19 2.03 l
3.0 0.16 0.00 0.93 0.58 2.66 1.69 1
3.1 0.00 0.70 0.84 0.53 2.22 1.41 3.2 0.00 0.00 0.73 0.46 1.85 1.17 3.3 0.70 0.00
~ 0.62 0.38 1.55 0.97 i
3.4 0.00 0.00 0.51 0.32 1.28 0.81 I
3.5 0.00 0.00 0.41 0.26 1.06 0.66 3.6 0.00 0 00 0.33 0.20 0.86 0.54 3.7 0.00 0.30 0.25 0.10 0.69 0.43 3.8 0.00 0
0.19 0.00 0.55 0.34 3.9 0.00 0
0.14 0.00 0.44 0.27 4.0 0.00 0
0.02 0.00 0.39 0.26 4.1 0.00 0
0.00 0.70 0.33 0.23 4.2 0.00 0
0.00 0.00 0.34 0.25 l
42 0.30 0
0.70 0.00 0 35 0.26 I
4.4 0
0 0.00 0.00 0.31 0,23 4.5 C
0 0.00 0.00 0.26 0.19 4.6 0
0 0.00 0.30 0.22 0.02 4.7 0
0 0.00 0
0.19 0.00 4.8 0
0 0.30 0
0.13 0.00 l
49 0
0 0
0 0.00 0.70 5.2 0
0 0
0 0.70 0.00 5.4 0
0 0
0 0,00 0.30 5.7 0
0 0
0 0.30 0
TOTAL 132.01 104.39 248 65 195.46 454.38 344.54
>1V 61.IB 41.73 121 80 83.84 269.50 185.04
>2V 8 62 5.20 23 23 15.19 74.99 48 87 Prodcomp.als Tse 6 2 7/1298 4 26 PM g
[
T;bb 6-3 Firley Unit 2 April 1996 Compari:on tf Predicted cnd Actu;l EOC 12 V ltrge DiItributi:ns Steam Generator A SteamGeneretor B Steam Generator C Number of Indics,tione EOC 12 f EOC 12 Prediction EOC-12 Prediction EOC-12 EOC 12 Prediction EOC-12 Voltage Sin POD = 0.6 l POPCD Actual POD = 0.6 POPCD Actual POD = 0.6 POPCD Actual 0.2 0.05 0.06 0
0.02 0 03 0
0 00 0.00 0
0.3 0.46 0.61 1
0 41 0.51 4
0.22
~
0.25 7
i
_ 0. 4_
_ _1 49. __ _ 1.86 4
223 2.53 9
1.84 1.97 6
0.5 2.92 3.21 14 6 08 6 40 15 5.56 5.62 19 0.6 5.21 5.13 8
10.79 10.58 14 to 47 10.05 30 0.7 7.73 7.05 10 1423 1313 13 15.51 14.13 04 0.8 9.10 7.81 4
16.29 1423 16 19.86 17.21 24
_ 0.9 _ _ _ 9.39_.
. 7.63.,
. _6_
_,16.15_ _
_ 13.51_
.,_15 __.
_ _ 22.66
,18J1 17 1.0 8.78 6 85 4
14.62 11.81 5
_ 23.65 18.78 21 e
1.1 7.70 5.82 1
1A06 10.19 10 23.02 17.70 14 12 6.59 4 88 5
11 95 9 01 11 21.18 15.82 13 1.3 5.61 4.06 4
1126 828 9
19.10 13.91 10 14 4 83 3 45 7
10.61 7.65 5
17.35 12.43 11 1.5 4.19 2 97 4
9Y9 6.98 1
16.15 11.38 14
{1.6
, [3.76][ ~ 2 6{..[3 [ [ 8 68
. [ 6.13
[ 7[ _
~ [ 15.31. '
10.60 1
_ 10 1.7 3.48 2.39 2
7.29 5.10 0
14 49 9 87 11 18 3 27 222 0
5.84 4 06 6
13.58 9.05 7
1.9 3.02 2.01 0
4.51 3.12 2
12.57 821 7
)
2.0 2.72 1.77 0
3.38 2.34 3
11 44 7.30 7
2.1 2.39 1.50 2
2.51 1.72 0
10.18 6.33 3
1 22 2.08 124 1
1.86 126 2
8 94 5.37 4
2.3 1.81 1.00 0
1.37 0.92 0
7.75 4.46 3
2.4 1.57 0.83 0
1.03 0.69 0
6.65 3.66 2
.._ 2.5_
_. _1.37_
_ 0.69
._1_,. _.. 0.85 _
___0.57_ _ __0_
__, 5.69 _
3.02 _
_2 2.6 120 0.59 0
0.78 0.54 0
4.95 _.
2.58 5
3 2.7 1.07 0.54 0
0.75 0.53 1
4.30 2.19 0
{
2.8 0 92 0.48 0
0.77 0.55 0
3.84 1.93 2
l 2.9 0.78 0 41 0
0.76 0.54 1
3.46 1.71 0
3.0 0.64 0.35 0
0.70 0 49 1
3.09 1.47 0
31 0.51 027 0
0 63 0 44 1
2.73 1.24 0
32 0.39 0.14 0
0 55 0.38 0
2.39 1.03 0
3.3 0.30 0.00 0
0.47 0.32 0
2.06 0.83 2
3.4 022 0.00 0
0 41 028 0
1.77 0 66 0
35 0.12 0.70 0
0.35 0.24 0
1.54 0.54 0
3.6 0.00 0.00 0
0.30 0.20 0
1.35 0.45 0
3.7 0.00 0.00 0
0.24 0.01 0
120 0.38 0
-.-3.8
--0.00.-.
-_. 0.00--
.-0
. 0.16 _
0.00.,
0
. 1.08._
0.33.
0 4.0 0.00 0.00 0
0.00 0.70 0
0 85 024 0
4.1 0.00 0.00 0
0.00 0.00 0
0 74 0.19 0
42 0.00 0.30 0
0.70 0.00 0
_ 0.64_
. 0.16 C
l 4.3 0.00 0
0.00 0.00 0
0 55 0.12 0
_ 4.4 _
. _.0.00..
_ 0, _
_ 0.00_ _
0.00 0
0.47 0.09
_0 4.5 0.00 0
0 00 0.00 0
0.40 0.07 0
._ 4 6., _
0.00 0
0.00 _
. _0.00_.,0____
._. 0.33 0.05 _
0 4.7 0,00 0
0.00 0.00 0
028 0.04 0
48 -
_. 0. 30_
_O_
_0.00 _ _
_ 0.00 _,. _O._
0.23
_ 0.03 0
4.9 0
0.00 0.00 0
0.19 0.02 0
5.0 0
_ 0.00.. _..._ 0 00 O
0.16 0.01
_0 l
_5.2 _ _
O _
_, 0.00 0.00 _,
0_..
_ 0 14 0.02 0
_ _ 51_
0 l
5.3 0 _
0.00. _ _
0.00 _.
._0_
_ 0.17
_0.07 0
0.00 0.00 0
0.19 0.00 0
l
- 5. 4. _
0_
_ _0.00
, 0.30,
._ 0
_ _0.19 0.00 0
I
.,5.5 _
0
_ _ 0 00._ _ _
_0 020 0.00 0
5.6 0
0.30 _
0 0.19 0.70 0
5.7 0
0 0.17 0.00 0
. _ 5.8, _
0 0._ _
._ 0.11 0.00,
0 j
_0_
_ 0.14 0.00 _
.0
_ 5.9 0 _.
_, 6.0.
.0
_._0,_
_ 0.09 0.00 0
i 6.1_
0_
_ 0
__0 00_ _
_0.00,
0 6.2 0
0 0.08 0.30 0
6.3
.0_.
- __0,
__0.07 0
64 O __
.O.
0.07 0
6.5 0
0 0.04 0
7.0
_0
.0
. _0.70 0
76 0
0 0 30 0
TOTAL 106 67 61 43 81 00 182 68 146 27 151.00 345.66 243 56 ! 275 00
=1V 61 54 4122 30 00 101.86 73 54 60 00 245 89 156 84 ! 127 00
- 2V 16 37 9 04 4 00 15 49 10 68 6 00 81 70 40 57 1 23 00 I
l mamm ew G-7 I
- 3 s
t n
a
- 2 l
5 P
8]
1 n
i -
m s
u n
od n
it c e ed pd
- 2 sA 6
n 0
0 I
5 8
=
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7 n -
oP P -
1 6 d N d -
e eet r s ta r
ua o d
M-p n
- 5 B gB a
e i
F nR 1
oI C
iR uP R
t N-b i E r
t n
isi D de Dt n
Ce 1
P s e
Or PP ic[
e r
n e
G
- 5 0
O 0
9 8
7 6
5 4
3 2
1 0
1 0
0 0
0 0
0 0
0 0
0
$. 2 %= * = 5 E.E.
v.
Figure 6-2 Farley Unit 2 SG-A Predicted Bobbin Voltage Distribution for Cycle 13 Combined Data for Hot and Cold Leg Indications r.
POD = 0.6 l
l 25 l
0 1
20 -
O BOC-13
=
l i
y 35 I
E Pred EOC-13 l
e c
~
l l 8 I
l f 10 -
!E l
~
I 5
t o
- E '"
"- -- E 020.304050.601080.91.01.11.21.31.41.51.61.71.81.92.02.1222.3242.52.62.72.82.93.03.34.3 Bobbin Voltage i
L F
._ _J I
EPRI POPCD I
25 t
1 D BOC-13
~
l2 I
i 15 p
W Pred EOC-13 1
o 10 -~
Y l
i i
~
l 5-O.
.B.
m.
E.-
020.3040.50.60.70.00.9101.1 121.314 151.61.71.81.92.02.1 2.22.3242.5262.72.831 37 l
^
Bobbin Voltage w- -. - -.
,,,s...~
6-9
1 i
Figure 6 3 j
Farley Unit 2 SG-B
{
Predicted Bobbin Voltage Distribution for Cycle 13 i
Combined Data for Ilot and Cold Leg Indications POD = 0.6 30 25 O BOC-13 g 20 g
t!
I E Pred EOC-13 35 z!
2 ?O
'I 5
l
{lfllisin na......_
[
Bobbin Voltage EPRI POPCD 25 20 O BOC-13 I0 g 15 E Pred EOC-13
'o 10 -
- ~ - -
1 i
5 I
lrlf!llimsisrw....__s.
1 Bobbin Voltage 6 10
Figure S-4 Farley Unit 2 SG-C Predicted Bobbin Voltage Distribution for Cycle 13 Combined Data for Hot and Cold Leg Indications f
POD = 0.6 60 50 0 BOC-13 l n 40
!5
' liiio I
Ti m Pred EOC 13 g
{
,m e
! 2 20 l
10 f
l o
I Illiban...._______
Bobbin Voltage l
EPHI POPCD I
50 l
45 40 l
33 O BOC-13 l:
i
,o l
1 % 30 h
'.9v
$25 E Pred EOC 13 I
o I
go z
I 15 -
10 l
5 r! l E E E IIs n m _
l' 0
r 2 3 : : : : : : : : : : : : : : : : : : : : : :
l Bobbin Voltage l
l 1
{
l I
6-11
l a :
l e :
e.,
e I
~
as :
='
eq
=
s %
'a a
a, g
.a k
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d a-2 l
a l
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SuollB3lpu] 30 JegwnN
7.0 TUBE LEAK RATE AND TUBE BURST PROBABILITIES 7.1 Calculation of Leak Rate and Tube Burst Probabilities This section discusses tube leak and burst probability analyses using vo!tage distributions projected for the end of the operating period. The calculation utilizes correlations relating bobbin voltage amplitudes (either measured or calculated) to free span burst pressure, probability of leakage and associated leak rates for ODSCC indications at TSP locations. The methodology used is documented in Reference 9.3, and is consistent with NRC criteria and guidelines of References 9.1.
Leak rates based on the actual measured voltages are calculated using a leak rate correlation independent of voltage, and the leak rate calculations based on the projected EOC-13 voltages utilize the leak rate vs. bobbin voltage correlation shown in Section 4.0. The calculated leak rates are volumetric rates at room temperature and they should be with compared with allowable leak rates at room temperature.
j l
The latest ARC correlations available at the time of Farley Unit-2 EOC-12 inspection are documented in Reference 9.10. Since then, ARC correlations have been updated and the revised correlations are presented in Addendum-2 to the EPRI database report (Reference 9.7). NRC concurrence for the use of these correlations has not been obtained at the time of this report. Since the correlations in Reference 9.7 yields higher leak rate than those in Reference 9.10, EOC-13 projections were calculated using both sets of correlations.
7.2 Predicted and Actual Leak Rate and Tube Burst Probability for EOC-12 i
l Analyses were performed to calculate SLB tube leak rate and probability of burst for l
the actual bobbin voltage distribution at EOC-12 (with no growth projection applied) previously presented in this report.
The results of Monte Carlo calculations performed based on the actual voltage distributions including NDE uncertainties are shown on Table 7-1. Projections for EOC-12 conditions for all three SGs presented in the last 90-day report are also included for comparison in Table 7-1. The allowable SLB rate for the last operating cycle (Cycle 12) was 23.8 gpm (at room temperature).
i Two sets of calculations available for EOC-12 projections:
l i)
Original analysis performed after the EOC-11 outage using the ARC database submitted to the NRC as documented in Reference 9.9.
ii)
Updated analysis for the limiting SG (SG-C) performed during Cycle 12 including UOAs with PIs and applying an updated ARC database which q:\\ ape \\apr98\\apr90 day. doc 7-1 I
t
1 I
i included 1996 Farley-2 and 1997 Farley-1 pulled tube data.
For SG-C, analysis based on the actual EOC-12 voltages was performed using both of i
the ARC databases considered for projections. SLB leak rates were calculated using a leak rate correlation independent of bobbin voltage.
Comparisons of the EOC-12 actuals with the corresponding predictions indicate the following:
a)
The actual number ofindications found during EOC-12 inspection in all SGs are significantly below those projected during the last outage using POD =0.6, 1
but slightly higher than that obtained with POPCD for SGs B and C. The peak voltages measured for all three SGs are lower than projected with both
{
POD =0.6 as well as POPCD.
i b)
SG-C was projected to be the limiting steam generator for EOC-12 based on EOC-11 data, and it was confirmed to be limiting based on the actual bobbin 1
measurements for EOC-12. For all SGs, SLB leak rates based on the actual voltage distributions are less than those projected with POD =0.6 as well as POPCD; they are also well below the acceptance limit (23.8 gpm at room temperature),
c)
For all SGs, tube burst probabilities based on the actual voltage distributions are less than the projections with POD =0.6 as well as POPCD; they are also below the NRC reporting guideline of10 2, d)
SLB leak rates and burst probabilities reported originally in the last 90-day report are conservative. The updated projection analysis for SG-C in which the UOA population was treated like PIs is overly conservative.
In summary, the limiting SLB leak rate (2.4 gpm at room temperature) and tube btust probability (2.3x104 ) calculated using the actual measured EOC-12 bobbin voltage distributions and an updated ARC database that includes recent Farley pulled tube test data are well below the corresponding allowable limits (23.8 gpm and l
10 2, respectively). The results meet the ARC requirement for continued operation.
7.3 Projected Leak Rate nnd Tube Burst Probability for EOC-13 I
Using the methodology previously described, calculations have been performed to predict the EOC-13 performance of all three steam generators in Farley Unit-2, and the results are summarized in Table 7-2. EOC-13 bobbin voltage distributions as well as the leak rates and tube burst probabilities based on these distributions are q:\\apc \\ apr9M apr90 day. doc 7-2
l l
predicted. As mentioned earlier, EOC-13 leak rates and tube burst probabilities are l
calculated using ARC correlations presented in both References 9.7 and 9.10. The projected leak rates are compared with the allowable leak rate at room temperature (23.8 gpm). The leak rate vs. bobbin voltage correlation shown in Section 4.0 is applied.
SG-C has both the highest number of indications as well as the largest indication returned to service for Cycle 13; therefore, it was projected to be the limiting SG.
Since growth rate for Cycle 11 is higher than that for Cycle 12, Cycle 11 growth data were used in the EOC-13 projection analysis. The predicted EOC-13 SLB leak rate and burst probability for all three SGs are shown in Table 7-2. ARC correlations in Reference 9.7 yield higher SLB leak rates than the correlations in Reference 9.10.
The limiting EOC-13 SLB leak rate predicted for SG-C based on constant POD of 0.6 is 2.0 gpm (room temperature) which is well below the current licensed limit of 23.8 gpm at room temperature. This projected EOC-13 leak rate is below that based on the actual measured EOC-12 voltages (2.4 gpm) because it is obtained using voltage-dependent leak rates whereas the latter value is based on a leak rates independent of voltage.
The limiting EOC-13 burst probability (also predicted for SG-C with POD =0.6) is projected to be 6.5x104 using the ARC correlations revised in Reference 9.10; it is well below the NRC acceptance limit of 10-2 Thus, projected EOC-13 results meet the ARC requirement for continued operation.
In summary, SLB leak rates and tube burst probabilities projected for EOC-13 for all three SGs using the NRC-mandated POD = 0.6 meet the SER limits for Farley Unit-
- 2. Results based on voltage dependent PO'PCD show even a greater margin between EOC-13 predictions and acceptance limits.
q:\\apc\\apr98\\apr90 day. doc 7-3 4
Table 7-1 Farley Unit 2 1997 EOC-12 Outage Summary of Calculations of Tube Leak R, ate and Burst Probability Number SLB Steam POD of Max.
Burst Probability Leak Gcnerator Indications'"
Volts Rate (Epm) 1 Tube 1 or More Tubes EOC - 12 PROJECTIONS (Based on ARC Database Presented in Reference 4 - Leak Rate Correlation Not Used)
A 0.6 106.7 4.8 1.6x10" 1.6x10" 1.0 B
0.6 178.7 5.6 1.8x10*
1.8x10" 1.4 C
0.6 345.7 7.6 1.2x10~"
1.2x10~"
5.1 A
POPCD 81.4 4.2 1.1x10" 1.1x10" 0.6 B
POPCD 142.3 5.4 1.9x10" 1.9x10" 1.0 C
POPCD 243.5 6.2 3.6x10" 3.6x10*
2.6 C"
0.6 437.3 7.7 2.0x10'"
2.0x10" 9.3 EOC - 12 ACTUALS (Same ARC Database as Used in the Above Projections-Leak Rate Correlation Not Used)
A 1
81 2.4 1.9 x 10"'
1.9 x 10" 0.3 B
1 151 3.1 8.3 x 10" 8.3 x 10" 0.7 C
1 275 3.3 2.1 x 10*
2.1 x 10*
1.9 C'
1 275 3.3 2.3 x 10" 2.3 x 10" 2.4
~
Notes: (1) Adjusted for POD.
(2) Includes UOA calls in EOC-11 inspection.
(3) Updated ARC database including '96 Farley-2 and '97 Farley-1 pulled tube data applied.
q:\\ ape \\apr98 \\ apr90 day. doc 7-4
Table 7-2 Farley Unit 2 Summary of Projected Tube Leak Rate and Burst Probability for EOC-13 (Based on projected Cycle 13 length 459,8 EFPD)
Steam POD No. of Max.
Comments Generator Indic-Volts One or Leak More Rate ations")
1 Tube Tubes (gpm.m Updated ARC Database Reported in Reference 9.10 Applied A' '
132 4.3 1.2x10-4 1.2x10-4 0.2 Leak rate B' '
O.6 248.7 4.8 2.2x10 4 2.2x10-4 0.5 Correlation applied C' 4 '
454.3 5.7 6.5x10 4 6.5x10-4 1.4 ARC Database and Correlations Reported in Reference 9.7 Applied A' '
132 4.3 5.3x10-5 5.3x10-3 0.3 Bia 0.6 248.7 4.8 2.1x10-4 2.1x10 4 0.8 C' ' '
454.3 5.7 5.6x104 5.6x10 4 2.0 Leak rate Correlation A' 8 '
104.4 3.7 5.8x10-5 5.8x10-5 0.2 applied B<ai POPCD 195.4 4.6 1.7x10-4 1.7x10 4 0.5 i
l C*
344.5 5.4 3.7x10 4 3.7x10-4 1.4 l
Natu l
(1) Number ofindications adjusted for POD.
(2) Volumetric leak rate adjusted to room temperature.
(3) All SG ccmposite growth rate distribution applied.
(4) SG-C specific growth rate distribution applied.
l l
q: \\ apc\\ apr98 \\ apr90 day. doc 7-5
l 1
I I
1 8.0 UPDATED PROBABILITY OF PRIOR CYCLE DETECTION FOR 19 INSPECTIONS IN 10 PLANTS i
The evaluation of the POPCD for Farley Unit-2 EOC-11 inspection based on the EOC-12 inspection results is described in Section 3.4. At this time, POPCD evaluations are l
available for 23 inspections at 10 plants, including four evaluations for Farley Unit-2.
L The available data include 15 inspections of plants with 7/8" diameter tubing and 8 inspections of plants with 3/4" diameter tubing. A generic POPCD distribution has
=
been developed based upon available POPCD evaluations (Reference 9.7).
This section updates the generic POPCD distribution by including Farley Unit-2 EOC-11 data. The POPCD evaluations performed since 1992 show significant improvement over the earlier assessments that represent the first ARC inspections. Bobbin data analysis guidelines (Appendix A guidelines) have been revised since the first inspections to reflect the initial ARC experience. Thus, it is appropriate to assess POPCD for inspections performed since 1992. Nineteen of the 23 inspections for which POPCD has been evaluated were performed since 1992.
Table 8-1 shows the combined POPCD evaluation for plants with 7/8" diameter tubing, and it includes results for 12 inspections performed since 1992. These data are also plotted in Figure 8-1, and they include data from the present Farley Unit-2 assessment (EOC-11 results representing 1995 inspection) as well as the data for the EOC-10, EOC-9 and EOC-8 inspections (data for EOC-10, EOC-9 and EOC-8 inspections are reported in References 9.4 and 9.5). The POPCD value approaches unity at about 3 volts. The addition of Farley-2 EOC-11 POPCD distribution to the generic database for 7/8" tubes increases the average value of the composite data (independent of voltage) slightly from 0.72 to about 0.725. Although the Farley-2 EOC-11 POPCD values are much higher than the composite average, the increase in the composite average value is not significant because of the very large indication population in the POPCD database (database for 7/8" tubes includes over 15600 indications). POPCD values in the volt range 1.2 to 3.2 volts are still below those observed in the EPRI study on detection probability for a dual analyst team.
Table 8-2 and Figure 8-2 show the combined POPCD evaluation performed for plants with 3/4" tubing considering 6 inspections since 1992. These results are same as those presented in Reference 9.7 since no new data is available for 3/4" tubes.
The definition of POPCD includes indications which were not present at the prior inspection and thus could be expected to be somewhat lower than the EPRI POD which is based on " expert" evaluations of inspection results and does not include indications clearly below detectable levels.
i
(
)
q:\\ ape \\ apr98 \\ apr90 day. doc 8-1 l
l l
The combined data for the 19 inspections since 1992 are given in Table 8-3 and the POPCD evaluation is shown in Figure 8-3 for RPC confirmed plus not inspected indications.
It is seen that the inspections since 1992 yield a POPCD in good agreement with the EPRI POD which was a 1994 evaluation. POPCD supports a POD approaching unity at about 3.5 volts while the EPRI dual analyst detection probability is about 0.98 at 2 volts and unity at 3 volts. Figure 8-3 also includes POPCD evaluated at the lower 95% confidence limit on the data for individual voltage bins.
e The POPCD evaluations shown in Figures 8-1 to 8-3 are based on the definition of
" truth" as RPC confirmed plus not RPC inspected indications. Since many of the indications not RPC inspected would be expected to be found NDD ifinspected, this represents a lower bound POPCD evaluation.
Figure 8-4 shows the POPCD evaluation for all 19 inspections since 1992 based only on RPC confirmed indications.
Thses results show a significant increase in POPCD below 1.5 volts and a modest increase above 1.5 volts, relative to the data in Figure 8-4. The data of Table 8-3 show about 850 to 28000 indications in all voltage bins below 2 volts, about 400 between 2.0 and 3.2 volts and about 10 indications above about 3.2 volts. Thus, the collective data provide a substantial database for defining a POD.
The results of Figure 8-3 clearly support an increase in the POD for ARC applications above the POD = 0.6, independent of voltage, required by NRC Generic Letter 95-05.
For indications above 1.0 volt, the POD exceeds 0.9 and is 0.95 to near unity at 2.0 l
volts. A POD of 0.6 is only applicable to indications below about 0.6 volts.
1 l
A recommended voltage dependent POD distribution has been developed for ARC
]
application by evaluating POPCD at the lower 95% confidence level and smoothing the resulting distribution. The recommended POPCD distribution is presented in Reference 9.7 and shown in Figure 8-5. The present Farley-2 EOC-11 daca was added to the POPCD database and the recommended distribution was updated.
The updated POPCD distribution is tabulated in Table 8-4 and compared with the EPRI
~
dual analyst detection probability in Figure 8-6. Table 8-4 shows both the POPCD distribution presented in Reference 9.7 and the presently updated distribution.
Although the Farley-2 EOC-11 POPCD values are much higher than those obtained from the recommended distribution, the addition of the present Farley-2 data did not significantly change the recommended distribution because of the large size of the POPCD database (nearly 48,000 indications in the database versus 520 indications in Farley-2 evaluation).
q:\\apc\\apr98\\apr90 day. doc l
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Table 8-4 Comparison of EPRI POPCD with EPRI POD Study EPRIPOPCD l
Voltage EPRl" POD NP-7480-L Updated Study AddeMum-2
~
0.1 0.30 0.26 0.26 l
0.2 0.38 0.36 0.36 0.3 0.49 0.46 0.46
~
0.4 0.57 0.54 0.54 0.5 0.62 0.63 0.63 0.6 0.66 0.69 0.68 0.7 0.71 0.75 0.74 0.8 0.76 0.79 0.78 0.9 0.80 0.82 0.81 1
0.83 0.84 0.84 1.2 0.90 0.87 0.'87 1.4 0.93 0.89 0.90 1.6 0.96 0.91 0.91
'8 0.98 0.92 0.92 2
0.984 0.93 0.93 4
3 1.00 0.98 0.98 3.5 1.00 1.0 1.0
- Dual analyst detection probability study e
e compoped x!s Table 8 4 7/9S8 5 02 PM 8-6
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9.0 REFERENCES
l 9.1 NRC Generic Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking", USNRC Office of Nuclear Reactor Regulation, August 3,1995.
9.2 Safety Evaluation Report, " Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No.115 to Facility Operating License NPF-8, Southern Nuclear Operating Company, Inc., Joseph M. Farley Nuclear Station, Unit 2, Docket No. 50-364", United States Nuclear Regulatory Commission, October 11,1996.
9.3 WCAP-14277, Revision 1, "SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections," Westinghouse Nuclear Services Division, December 1996, 9.4
. SG-97-03-001, "Farley Unit-21996 Alternate Repair Criteria 90 Day Report,"
Westinghouse Nuclear Services Division, March 1997.
9.5 SG-95-07-010, "Farley Unit-2,1995 Interim Plugging Criteria 90 Day Report,"
Westinghouse Electric Corporation, July 1995.
9.6 WCAP-12871 Revision 2, "J. M. Farley Units 1 and 2 SG Tube Plugging Criteria for ODSCC at Tube Support Plates", Westinghouse Electric Corporation, Proprietary Class 2, February 1992.
9.7 Addendum-2 to EPRI Report NP-7480-L, " Steam Generator Outside Diameter Stress Corrosion Cracking at Tube Support Plates - Database for Alternate Repair Criteria," April 1998.
l 9.8 Letter from B. W. Sheron, Nuclear Regulatory Commission, to A. Marion,
{
Nuclear Energy Institute, dated February 9,1996.
l 6
I 9.9 NSD-SGD-1212, "EPRI ARC Databases for 3/4" and 7/8" Dia. Tubes and Updated ARC Correlation for 7/8" Dia. Tubes," Westinghouse memorandum dated February 26, 1996 transmitted to Duquesne Light Company and Tennessee Valley Authority.
9.10 Letter from R. Clive Callaway, Nuclear Energy Research Institute, to Nuclear Regulatory Commission, " Updated ODSCC ARC Correlations for 7/8" Diameter Tubes," dated December 29,1997.
q:\\apc\\apr98\\apr90 day. doc 9-1
l l
Appendix A Resp <mse to NRC Request for Additional Information on the Last 90-Day Report This appendix presents response to NRC's request for additional information on the
]
last 90-day report (Reference A-1) for Farley Unit-2 submitted via Reference A-2.
1.
Submit the current accident leak rate assessment for the end-of-cycle 12 (EOC-
- 12) at Farley Unit-2. Include specific references to any changes in the Bases from which this value was calculated as compared to the subject 90-day report (e.g., the indications included in the beginning-of-cycle population now includes
" unusual outside diameter phase angle" indications (UOAs), the data base now includes the latest Farley Unit 1 tube pull result, etc.)
Response: Response to this question has been provided earlier in Reference A-2.
2.
Discuss the various characteristics SNC has evaluated in an effort to understand the growth rate behavior of outside diameter stress corrosion cracking (ODSCC) located at the tube support plates (TSPs) in deplugged steam generator (SG) tubes. Include, at a minimum, in the response:
(a) the total number of deplugged tubes placed in service per SG. Include those tubes that have since been replugged.
(b) the cycle in which each tube was initially plugged, the cycle in which each tube was deplugged, and the cycle in which each tube was replugged. If a deplugged tube is still in service, so indicate. Include those tubes that were replugged without additional service time.
l (c) for each deplugged tube with ODSCC lccated at the TSPs, provide the voltage of the ODSCC indication (s) prior to plugging, just after deplugging, and the most recent voltage measurement.
Provide this information for all deplugged tubes, including those that have since been replugged and those that were replugged without additional service time.
(d) the location of the deplugged tubes in the SG (e.g., R56C115, first TSP).
(e) the appropriateness of using the growth rates of the ODSCC indications, during the time in which the tube was plugged, to predict the growth behavior of the indication (s) when the tube is placed back in service.
l Response: Growth rate data for ODSCC indications at TSPs in deplugged l
tubes returned to service in Farley Unit-2 and two other plants have been l
systematically evaluated and compared against growth rates for active tubes.
The original evaluation presented in the last 90-day report (Reference A-3) has been updated and presented in Section 3-4 of this report. Similar results for another plant are presented in Reference A-4. All available growth data i
for indications in deplugged tubes during the first and second cycles of operation following return to service are compared against the active tube q:\\apc\\aprs8\\apr90 day. doc
{
A-1 l
growth data. Growth when the tubes are inactive prior to deplugging are not included in the evaluation because the temperature and TSP crevice chemistry are expected to be significantly different than when the tubes are inactive which would affect the growth rate. Growth data for indications in inactive tubes are not used to project growth when the tubes are placed back in service.
Growth behavior of TSP indications should be evaluated using data obtained with bobbin voltages established using a consistent set of eddy current signal analysis guidelines. Since implementation of alternate repair criteria for TSP indications in 1992, bobbin voltage signals have been reevaluated using a consistent set of guidelines to reliably estimate growth rates. Therefore, only post '92 inspection data should be used to study growth behavior of TSP indications. During the EOC-10 and EOC-11 inspections for Farley Unit-2, a number of tubes were deplugged, inspected and those meeting the alternate repair criteria were returned to service. Eddy current data for indications in tubes deplugged during the EOC-10 and EOC-11 inspections are summarized in Table A-1. Data for both tubes returned to service and those that were i
replugged without additional service time are shown. As requested, the following information is presented for indications in each deplugged tube.
a) the location of the indication in the SG, b) the cycle in which the tube was initially plugged, c) the cycle in which each tube was deplugged, d) the cycle in which each tube was replugged, e) the voltage of the indication prior to plugging, f) the voltage of the indication just after deplugging, and g) all voltage measurements available after return to service.
Tubes that were replugged without additional service time and those still in service are identified in the comment column.
1 Indication growth rates while the tubes are inactive prior to deplugging are not used to project growth rates when the tubes are placed back in service.
When a tube is inactive, temperature and TSP crevice chemistry are expected to be significantly different from when the tube is active and, therefore, the growth rate is also expected to be different. Only growth data for tubes active for at least one cycle of operation are used to project EOC conditions for future cycles.
3.
The results of a sensitivity analysis on the projected tube leak rate and burst probability for EOC-12 are shown in Table 8-4 of the subject report. The staff
(
requests clarification of the information shown in Table 8-4.
There are four distributions: " Tubes in service Cycle 10," " Tubes deplugged EOC-10," "All l
indications (combined analysis)," and "All indications (based on EOC q:\\ ape \\apr98 \\ apr90 day. doc A-2
voltages)." For each distribution, clarify the growth rate distribution applied.
Specify whether the distribution is from a composite or SG specific distribution.
Specify whether the distribution is based on deplugged tubes, in-service tubes, or a combination ofboth.
Response: The purpose of the sensitivity analysis summarized in Table 8-4 of the last 90-day report for Unit-2 (Reference A-3)is to show that although the indication population in tubes deplugged at EOC-10 had significantly higher growth rates than those in tubes active during Cycle 10, a single analysis for the combined indication population in the active and deplugged tubes would yield the same leak rate and burst probability results as those calculated by performing separate analyses for the active and deplugged tube indication population. Since Cycle 11 growth rates are higher than those for Cycle 10, leak rate and tube burst probability analysis for the EOC-12 condition was performed using Cycle 11 growth rate data. Cycle 11 growth data already include increased growth rates for deplugged tubes. Therefore, no additional adjustment was necessary for the Cycle 11 growth data to account for potential higher growth rates for deplugged tubes.
To obtain the 95% confidence limit value for the SLB leak rate and tube burst probability at EOC-12 when the indication population in the active and deplugged tubes are considered separately, EOC-12 voltage distributions for the active and deplugged tube indications were obtained separately using appropriate growth ratas. The two EOC-12 voltage distributions were then combined (by simply adding the number ofindications in each voltage bin),
and SLB leak rate and tube burst probability were calculated for the combined EOC-12 voltage distribution. No NDE uncertainties were applied to the combined EOC-12 voltage distribution since they are already included while calculating EOC-12 voltage distributions for the active and deplugged tubes separately. SG-specific growth data were used for all SGs. (Footnote 4 in Table 8-4 in the last 90-day report (Reference A-3) states that all SG composite growth rate distribution was used, and it is incorrect.) Cycle 11 growth rates for indications in actim and deplugged tubes were calculated separately and applied to their respective population. Another set of EOC-12 SLB leak rate and tube burst probability were calculated by treating indications in both active and deplugged tubes as a single population. Again, SG-specific growth data were used for all SGs in this case also. A single growth distribution containing Cycle 11 growth for both active and deplugged tubes was used for each SG. Therefore, four different indication distributions were considered in this sensitivity analysis, and growth rate data applied for each type is summarized below.
q:\\ apc\\apr38 \\apr90 day. doc A-3
Indication Distribution Growth Data Applied SG-specific, Cycle 11 growth data Tubes in service Cycle 10 defined considering indications in tubes active during Cycle 10 only SG-specific, Cycle 11 growth data Tubes deplugged EOC-10 defined considering indications in EOC-10 deplugged tubes only All indications (based on EOC voltages)
No growth applied as already included in the projected EOC-12 voltage distributions obtained separately for indications in active and deplugged tubes.
[
All indications (combined analysis)
SG-specific, Cycle 11 growth data L
defined considering all indications in the SG
\\
4.
The staff understands that for current EOC-12 predictions, SNC took into account the growth rate of deplugged tubes by weighting the two separate distributions (one growth rate distribution for in-service tubes and a second growth rate distribution for deplugged tubes) by the number of each type of indication returned to service. Benchmarking would provide an assessment of the " weighted" distribution methodology. Discuss SNC's benchmarking results; i.e., how did the EOC-11 actual distribution of voltages compare with the EOC-11 predictions made using the " weighted" methodology? How did the EOC-12 actual distribution of voltages compare with the EOC-12 predictions made using the " weighted" methodology?
Response: Since the growth rates for Cycle 11 are higher than those for Cycle 10, leak rate and tube burst probability for the EOC-12 condition was performed using the Cycle 11 growth rate data. A large number of tubes were deplugged and returned to service at BOC-11, and Cycle 11 growth data already includes the increased growth rate for deplugged tubes. Therefore, no additional adjustment was necessary to the Cycle 11 growth data to account for potentially higher growth rates for deplugged tubes.
Furthermore, there were only four indications in tubes deplugged and returned to service at EOC-11. So, even if Cycle 11 growth data did not already include deplugged tube growth, adjustment to Cycle 11 growth per the recommended methodology would not be discernible because of the small number of deplugged tube indications (4) returned to service for their first cycle of operation following deplugging.
For a cycle in which tubes are deplugged and returned to service (first cycle of q:\\apc\\apr98bpr90 day. doc A-4
operation), if the growth rate data selected per the Generic Letter 95-05 guidelines (i.e., the larger of growth rates for the past two cycles) do not already include growth for the first cycle of operation of deplugged tubes, it was recommended in the last 90-day report that deplugged tube growth be added to the active tube growth data selected per the Generic Letter 95-05 guidelines. A detailed description of a recommended method for combining the growth data for active and deplugged tubes is provided in Reference A-5'.
The recommended method is benchmarked by comparing EOC-11 projections performed using a composite growth distribution determined per the recommended methodology with those based on the actual EOC-11 voltage distributions. Good agreement between the EOC-11 projections and results based on as measured voltages show that the recommended method is acceptable. Additional details on the benchmarking analysis may be found in Reference A-5. It is important to recognize that adjustments to growth rates for deplugged tubes are necessary only for the first cycle following deplugging.
Growth data for the later cycles include any differences in growth rates of deplugged tubes and no further adjustments are required.
A detailed comparison of the EOC-12 projections presented in the last 90-day report with those based on the auual measured EOC-12 voltages is presented in Sections 6 and 7 of this report. EOC-12 peak voltages, SLB leakage rates and tube burst probabilities for all SGs calculated using the actual measured voltages are well below those projected with both a constant POD of 0.6 as well as voltage-dependent POPCD.
5.
For SG "C," the staff performed confirmatory tube burst and leak rate calculations using the standard Generic Letter (GL) 95-05 methodology. The staff obtained a burst value nearly identical to SNC's and obtained a leak rate 2 It is noted that there are the following two typographical errors in Tables 8-6 and 8 7 in Reference A-5.
a) The second sentence in the Table 8-6 footnote should read "For example, number of Indications in the 0.1 volt growth bin is given by [(26/81)*97 + (20/111)*89]=47.2.
b) Missing feotnotes 6 through 7 in Table 8-7 are as follows.
(6) To obtain 95'7d95% leak rate and burst probability, EOC voltage distributions obtained separately for active and deplugged tube indications were combined and leak and burst calculation were repeated.
(7) A composite growth distribution obtained by combining growth data for active and deplugged tubes applied.
(8) Largest SG-specific growth applied for deplugged tube indications.
(9) No POD adjustment for deplugged tube indications.
4: \\ ape \\ apr98\\apr90 day. doc A-5
value 5% Larger than SNC. The staff expected to obtain significantly different r
values, in a less conservative direction, from SNC because SNC calculated the burst and leak rate values using a more conservative " weighted" methodology as compared to the standard GL 95-05 methodology. In an effort to understand this apparent discrepancy, provide a more detailed discussion of the " weighted" methodology than is currently available in the 90-day report.
Response: As noted in the response to the previous question, a more detailed description of the recommended method of combining active and deplugged tube growth rates and its validation is presented in Reference A-5. Application of GL 95-05 guidelines would require the use of Cycle 11 growth data for performing EOC-12 projections, and Cycle 11 growth already includes growth for deplugged tubes. Also, there were only 4 indications (all in SG-B) in deplugged tubes returned to their first cycle of operation at EOC-11 and even if the recommended methodology was applied no adjustment would have been needed for SGs A and C, and SG-B growth would have changed very slightly.
Therefore, it not surprising to see good agreement between the staffs calculations and the results presented in the 90-day report for EOC-12 projections.
6.
Discuss how UOAs contributed to the EOC-11 underprediction from the previous cycle. Discuss tube pull results, historical reviews, rotating pancake coil inspection results, etc., that support SNC's conclusion that UOAs need not be included as part of the implementation of the GL 95 05 voltage-based repair criteria.
Response: Significant differences between the leak rate and tube burst probability based on the measured EOC-11 voltages and EOC-11 projections were found only for SG-C. EOC-10 inspection data for SG-C included 232 PIs and 32 UOAs. Thirteen of the UOAs had a bobbin voltage above 1.5 volts and 6 were above 2 volts. EOC-11 projections for SG-C were repeated including the EOC-10 UOA indications, and the inclusion of UOAs increased the projected EOC-11 SLB leak rate from 1.8 gpm to 2.7 gpm. Fifty-five indications were called as UOAs in SG-C during the EOC-11 inspection and those indications are not included in the SLB leak rate based on the actual EOC-11 voltage data presented in the last 90-day report. Inclusion of those 55 UOA indications in the leak rate calculations increases the actual EOC-11 leak rate from 2.7 gpm ta 3.7 gpm. Therefore, when the UOA population in both EOC-10 and EOC-11 inspections are included, the projected EOC-11 leak rate still underestimates that based on the actual measured voltages. Projected EOC-11 tube burst probability including EOC-10 UOAs (3.0x104) is also below that calculated q:\\ apc\\apr98 \\ apr90 day. doc A-6
including the UOAs in the measured EOC-11 voltages (8.0x10 4).
- Thus, l
underprediction of the EOC-11 SLB leak rate and tube burst probability for SG-C cannot be attributed to exclusion of UOAs; it is attributable to increased growth rates forindications in deplugged tubes returned to service.-
It was recommended in the last 90-day report (Reference A-3) that the Farley SG EC guidelines be modified to call indications with near 0% depth (formerly UOAs) as PIs and eliminate the UOA call from the criteria. This charce in the guideline was implemented in the recent (EOC-12) inspection, and it :acreased the number of the PI calls. As noted in Section 3.1, out of the 108 indications called as UOAs in EOC-11 inspection,103 were called as PIs in the EOC-12 inspection, one as INR (indications not reportable) and the remaining 4 were not detected. Therefore, essentially all last inspection UOA's were called as PIs in the recent inspection. UOAs call will not be utilized in the future inspection.
Previously, UOAs were not included in the GL95-05 leakage and burst analyses as phase angles near 0% depth are conventionally not classified as flaws.
The UOA classification was created to further evaluate such indications.
UOAs were included in the RPC sampling plans at each inspection and none were confirmed as flaws by the RPC inspection. UOAs were tracked from cycle to cycle to determine if they became RPC confirmed flaws in later cycles.
For example, only one UOA at EOC-11 became a confirmed flaw at EOC-12 out of 19 EOC-11 UOAs inspected at EOC-12, all of which were above 2 volts. This tracking confirmed that UOAs are either not flaws or flaws too shallow to be detected even by + Point inspection. The EOC-12 inspection guideline fbr including UOAs as PIs in the GL95-05 analyses is therefore very a conservative application that includes many more RPC NDD indications at significant voltages in the leakage and burst analyses. The decision to include UOAs as PIs was made due to the sensitivity of calling UOAs at <1% depth to the phase angle calibration even though the + Point inspections continue to show UOAs as NDD.
References A-1 Letter from J. I. Zimmerman, Nuclear Regulatory Commission, to D. N. Morey, Southern Nuclear operating Company, dated February 5,1998.
A-2 Letter from D. N. Morey, Southern Nuclear operating Company, to U. S.
Nuclear Regulatory Commission, dated March 9,1998.
q:\\ ape \\apr98 \\apr90 day. doc A-7
A-3 SG-97-03-001, "Farley Unit-21996 Alternate Repair Criteria 90 Day Report,"
l Westinghouse Nuclear Services Division, March 1997.
A-4 SG-98-03-003, " Beaver Valley Unit-1, Cycle 13 Voltage-Based Repair Criteria 90 Day Report," Westingh'use Electric Corporation, March 1998.
A-5 Addendum-2 to EPRI Report NP-7480-L, " Steam Generator Outside Diameter Stress Corrosion Cracking at Tube Support Plates - Database for Alternate Repair Criteria," April 1998.
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