ML20217D399
| ML20217D399 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 03/31/1998 |
| From: | WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20217D389 | List: |
| References | |
| NUDOCS 9804240297 | |
| Download: ML20217D399 (57) | |
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l BEAVER VALLEY UNIT - 1 CYCLE 13 VOLTAGE-BASED REPAIR CRITERIA 90-DAY REPORT March 1998 O
Westinghouse Electric Company l
i Energy Systems Business Unit Nuclear Services Division P.O. Box 158 Madison, Pennsylvania 15663-0158 9804240297 980416 PDR ADOCK 05000334 P PDR
BEAVER VALLEY UNIT - 1 CYCLE 13 VOLTAGE-BASED REPAIR CRITERIA 90-DAY REPORT l
March 1998 I l
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Table of Contents Page No.
1.0 Introduction 1-1
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2.0 Summary and Conclusions 2-1 I 3.0 EOC-12 Inspection Results and Voltage Growth Rates 3-1 l 3.1 EOC-12 Inspection Results 3-1 ,
3.2 Voltage Growth Rates 3-2 3.3 NDE Uncertainties 3-6 l 3.4 Probability of Prior Cycle Detection (POPCD) 3-7 l 3.5 Assessment of RPC Confirmation Rates 3-8 3.6 Probe Wear criteria 3-9 4.0 Database Applied for Leak and Burst Correlations 4-1 5.0 SLB Analysis Methods 5-1 l
l 6.0 Bobbin Voltage Distributions 6-1 6.1 Calculation of Voltage Distributions 6-1 6.2 Probability Of Detection (POD) 6-2 6.3 Limiting Growth Rate Distribution 6-2 6.4 Cycle Operating Period 6-3 6.5 Projected EOC-13 Voltage Distributions 6-3 6.6 Comparison of Actual and Projected EOC-12 Voltage Distributions 6-4 7.0 SLB Leak Rate and Tube Burst Probability Analyses 7-1 7.1 Leak Rate and Tube Burst Probability for EOC-12 7-1 7.2 Leak Rate and Tube Burst Probability for EOC-13 7-2 8.0 References 8-1 5:\apc\dlw97\Cyc1cl3,90d. doc 1
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i Beaver Valley Unit - 1 Cycle 13 Voltage-Based Repair Criteria 90-Day Report 1.0 Introduction This report provides a summary of the Beaver Valley Unit-1 steam generator (SG) bobbin and rotating pancake coil (RPC) probe inspections at tube support plate (TSP) intersections together l with postulated Steam Line Break (SLB) leak rate and tube burst probability analysis results.
I These results support continued implementation of the 2.0 volt voltage-based repair criteria for Cycle 13 as outlined in NRC Generic Letter 95-05 (Reference 8-1). Information required by the t
Generic Letter is provided in this report including SLB leak rates and tube burst probabilities l calculated using the end of cycle (EOC) conditions for the recently completed cycle (Cycle 12) and projection of bobbin voltage distributions, leak rates and burst probabilities for the ongoing j cycle (Cycle 13).
t l Analyses for Cycle 12 were carried out using the actual bobbin voltage distributions measured I
during the EOC-12 outage and the results compared with corresponding values from projections performed bz-M on the last (EOC-11) bobbin voltage data (presented in Reference 8-2). These evaluations ur axi the Westinghouse generic Monte Carlo methodology presented in Reference 8-3.
Analyses were also performed to project leak rates and tube burst probabilities for postulated SLB conditions at the end of the ongoing cycle (Cycle 13) based on the 2.0 volt repair criteria.
These analyses utilized bobbin voltage distributions measured during the recent (EOC-12) inspection and a limiting growth rate distribution from the last two inspections (EOC-11 and EOC-12 inspections).
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2.0 Summary and Conclusions l
A total of 2910 axial outside diameter stress corrosion cracking (ODSCC) indications were found during the EOC-12 inspection in all three SGs combined, of which 853 were inspected with a RPC probe, and 670 were confirmed as flaws. The RPC confirmed indications included
, 244 indications above 1.0 volt. The largest number of bobbin indications,1241 indications, l were found in SG-A; 396 of those were inspected by RPC, and 309 were confirmed as flaws.
Only three indications were found above 2 volts in all SGs combined, all located in SG-A, and ,
l confirmed by RPC. No circumferential indications, axial indications extending outside the TSP
- or volumetric-type signals were identified by RPC inspection at TSP distorted signal indication i locations. RPC inspection of dented intersections also did not show any circumferential indications or primary water stress corrosion cracking (PWSCC).
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l SLB leak rate and tube burst probability analyses were performed for the actual EOC-12 bobbin voltage distributions as well as the projected EOC-13 bobbin voltage distributions. EOC-12 actual measured bobbin voltages are all lower than the projections performed using the EOC-11 outage bobbin voltage data and constant probability of detectica (POD) of 0.6. The actual l number of indications detected during the EOC-12 inspection for all SGs are also below their corresponding projections. The SLB leak rate and tube burst probability values based on the
- actual measured voltages show significant margins relative to their pmjected values. SG-B was l predicted to be the limiting SG at EOC-12 as it had a slightly higher projected SLB leak rate and burst probability than SG-A; however, SG-A was found to be limiting based on the measured l data.
For the actual EOC-12 bobbin voltage distributions, tl'e largest SLB leak rate is calculated for )'
SG-A, and its magnitude is 0.3 gpm with the leak rate correlation and 2.4 gpm without the leak rate correlation. This leak rate value is substantially lower than the current allowable SLB leakage limit of 8.0 gpm as well as the previous limit of 4.5 gpm. All leak rate values quoted l are equivalent volumetric rates at room temperature. The limiting conditional tube burst probability based on the EOC-12 actual measured voltages, 9.7x10" also predicted for SG-A, is I
well below the NRC reponing guideline of 102 . The leak rate and burst probability values based on the actual EOC-12 voltages are calculated using an updated alternate repair criteria ,
(ARC) database that includes 1996 Plant A-2 and 1997 Plant A-1 pulled tube data. This database is applied as it yields a SLB leak rate more conservative than the current NRC l
approved database. The projected SG-A EOC-12 burst probability was 1.2x104 and the SLB leak rate was 4.3 gpm. These results exceed those obtained from the actual distributions even though the latter utilize a more conservative ARC database.
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SLB leak rate and tube burst probability projections were also performed for the EOC-13 conditions. SG-A is again predicted to be the limiting SG, and the EOC-13 leak and burst results for all three SGs are well within their allowable limits. Based on the NRC mandated constant POD of 0.6, EOC-13 SLB leak rate for SG-A is projected to be 1.0 gpm (room temperature), which is an order of magnitude below the current licensed limit of 8.0 gpm (room temperature). This limiting leak rate is also based on the updated leak rate and tube burst database, and it utilizes a leak rate versus bobbin voltage correlation. Per Reference 8-10, the test for the significance of a leak rate correlation can now be based on the p-value for the slope of the leak rate correlation determined on a one-sided basis (as opposed to a two-sided basis used until now). The slope parameter p-value for the 7/8" tube leak rate data determined on a one-l sided basis meets the 5% limit specified in Generic letter 95-05; consequently, a leak rate correlation can now Le applied for 7/8" tubes. De limiting burst probability, also calculated for 1 d
SG-A, is 1.9x10 ; it is about two decades below the NRC reporting guideline of 10 2, SLB leak rates were also calculated assuming that leak rate is independent of bobbin voltage as l in the prior 90 day reports. The limiting EOC-13 leak rate thus predicted (6.4 gpm) is about 6 l times of that obtained using the leak rate correlation; thus, there is margin even in the EOC-13 SLB leak rate projections based on the overly conservative methodology previously applied (no correlation).
Probability of prior cycle detection (POPCD) for the last (EOC-11) inspection was assessed using EOC-11 and EOC-12 inspection results, and the data strongly supports a voltage t dependent POD substantially higher than the NRC mandated POD value of 0.6. POPCD )
exceeds 0.6 at about 0.6 volt and remains above 0.90 beyond 0.8 volt. The Beaver Valley-1 EOC-11 POPCD distribution is slightly better than the generic POPCD distribution presented in 1 Reference 8-4.
The EOC-12 RPC confirmation rate for RPC no detectable degradation (NDD) indications left
- j. in service during Cycle 12 is only about 27%, which is well below the conservative 70% value applied to RPC NDD indications in the leak and burst projections for Beaver Valley Unit-1.
EOC-13 projections presented in this report were obtained including 70% of RPC NDD indications.
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l 3.0 EOC-12 Inspection Resuks and Voltage Growth Rates 3.1 EOC-12 Inspection Resuks According to the guidance provided by NRC Generic Letter 95-05, the EOC-12 inspection of the Beaver Valley Unit-1 SGs consisted of a complete,100% eddy current (EC) bobbin probe full length examination of the tube bundles in all three SGs. A 0.720 inch diameter probe was used for all hot and cold leg TSPs where voltage-based repair criteria were applied. Subsequently, RPC examination was performed for a minimum of 20 percent of the l hot leg indications with amplitude between 1 and 2 volts, and all hot leg indications with an l amplitude 2 volts and above. Only three indications were found above 2 volts in all three SGs
- combined, all located in SG-A; they were confirmed by RPC and removed from service. No ODSCC indications were found on the cold leg side at the TSPs. There were no circumferential
! indications at the TSPs, and no indications extending outside the TSPs. All bobbin indications at l TSPs with potential inside diameter (ID) phase angles were examined with RPC and I demonstrated to be outside diameter (OD) in origin. Dents 2 volts or larger on the hot leg side of the first three TSPs and all other TSP dents over 5 volts were also inspected with RPC; no circumferential or PWSCC indications were detected.
l A summary of the EC indications for all three SGs is shown on Table 3-1, which tabulates the number of field bobbin indications, the number of those indications that were RPC inspected, l
the number of RPC confirmed indications, and the number ofindications removed from service due to tube repairs. The indications that remain active for Cycle 13 opemtion are determined by l the difference between the observed indications and the indications removed from service. No I
tubes were deplugged in the current inspection with the intent of returning them to service after inspection in accordance with the ARC.
Overall, the combined data for all three SGs of Beaver Valley Unit-1 show the following:
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- Out of a total of 2910 TSP indications identified during the inspection, a total of 853 were RPC inspected.
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- Of the 853 RPC inspected, 670 were RPC confirmed.
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- Only three indications exceeded the 2 volt repair limit, all in SG-A.
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- A total of 2831 indications were returned to service for Cycle 13 operation.
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A review of Table 3-1 indicates that more indications (a quantity of 1198, with 108 indications above 1.0 volt) were returned to service in SG-A than the other SGs; thereby it potentially will be the limiting SG at EOC-13. It is noted that SG-A had all three indications above 2 volts ,
found in the EOC-12 inspection. j J
Figure 3-1 shows the actual bobbin voltage distribution determined from the EOC-12 EC inspection; Figure 3-2 shows the population distribution of those EOC-12 indications removed from service due to tube repairs; Figure 3-3 shows the distribution for indications returned to service for Cycle 13 operation. Of the 79 indications removed from service, only 3 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 .
The distribution of EOC-12 indications as a function of support plate location is summarized in Table 3-2 and plotted in Figure 3-4. The data show a strong predisposition of ODSCC to occur in the first few hot leg TSPs (2765 out of 2910 indications occurred at the hot leg intersections in the first three TSPs), although the mechanism extended to higher TSPs. No indications were .
detected on the cold leg side. This distribution indicates the predominant temperature dependence of ODSCC at Beaver Valley Unit-1, similar to that observed at other plants.
3.2 Voltage Growth Rates For projection ofleak rates and tube burst probabilities at the end of Cycle 13 operation, voltage growth rates were developed from EOC-12 (October 1997) inspection data and a reevaluation of the EOC-11 (April 1996) inspection EC signals for the same indications. Table 3-3 shows the i cumulative probability distribution for growth rate in each Beaver Valley Unit-1 steam generator during Cycle 12 (May '% - September '97) on an EFPY basis, along with the corresponding Cycle 11 growth rate distributions. Cycle 12 growth data are also plotted in Figure 3-5. The curve labeled ' cumulative' in Figure 3-5 represents averaged composite growth data from all three SGs. I Average growth rates for each SG during Cycle 12 are summarized in Table 3-4, and all three SGs show a negative average growth value. The average growth rates over the entire voltage i range vary between -19.2 % and -9.8% (of the BOC voltage) per EFPY, between SGs, with an overall average of -14.4% per EFPY. SG-B had the lowest growth (actually negative growth) among the three SGs, which explains why SG-B was not the limiting SG although it was projected to be limiting based on the prior cycle voltage data.
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I l The extent of negative gmwth rates found for Cycle 12 is unusual for ARC applications and potential contributing factors were reviewed. Since the negative growths are consistent across all SGs, the potential cause is judged to be independent of the SG inspected. After evaluating several potential contributing factors, it was concluded that the calibration technique used during the EOC-11 inspection to normalize the bobbin voltages had resulted in overestimation of the EOC-11 bobbin voltages by about 12.6%. Additional details on the evaluation carried out to investigate causative factors for apparent large negative growths are provided at the end of this section.
The cumulative probability growth distributions (CPDFs) for Cycles 11 and 12 and the average growth rates for the two cycles were reevaluated after reducing all EOC-11 voltages by 12.6%.
Tables 3-5 and 3-6 respectively show the revised CPDFs for Cycles 11 and 12 on an EFPY basis and the average gmwth rates for the three SGs. With the adjusted EOC-11 voltages, growth rates for Cycle 12 increase and Cycle 11 gmwths decrease: the average Cycle 12 growth rate of -16.3% before adjustment (Table 3-4) becomes about -3.8% after adjustment (Table 3-6), and the average Cycle 11 growth ute changes from 13.5% to about -0.9%. The CPDFs based on the growth data from all 3 SGs for Cycles 11 and 12 before and after adjusting the EOC-11 voltages are compared in Figure 3-6. Tables 3-7 and 3-8 respectively show the growth statistics for the last six operating periods with and without adjustment to the EOC-11 bobbin voltages. While the data in Table 3-7 indicate an abrupt rise and then a sudden drop in the growth rates for the last two cycles, the data in Table 3-8 show a more believable trend of progressively decreasing growth rates over the last six cycles. Therefore, the adjusted EOC-11 voltages provide a better representation of the growth rates.
The guidelines in Generic Ixtter 95-05 require the use of more conservative growth rate distributions fmm the past two inspections for projecting EOC distributions for the next operating cycle. It is evident from Figure 3-6 that the composite growth rates during Cycle 11 are higher than those during Cycle 12 with or without adjustment to the EOC-11 bohhin voltages. Therefore, Cycle 11 provides the more limiting cumulative probability distribution for growth for the last two cycles, and that gmwth distribution was used to develop EOC-13 l
predictions. Cycle 11 growth rates for SG-B are higher than the composite growth rates and, per the methodology presented in Reference 8-3, SG-specific growth rates are to be used for SG-B while the composite growth rates should be applied for the other two SGs. Although Cycle 11 growth rates based on the adjusted EOC-11 voltages are believed to be more realistic, unadjusted Cycle 11 growth rates shown in Table 3-3 were conservatively applied to obtain EOC-13 predictions.
During the prior two outages, (EOC-10 and EOC-11 outages), many tubes plugged earlier were deplugged and those meeting the current voltage based repair criteria were returned i
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to service. Recently, another plant with 7/8" diameter SG tubes experienced a significantly I higher growth among deplugged tubes returned to service (in comparison to active tubes). To examine the gmwth trends for deplugged tubes returned to service in Beaver Valley Unit-1, growth rates for the last two cycles were calculated separately for deplugged tubes and active tubes, and these results are included in Table 3-9. The average growth values shown are based !
on adjusted EOC-11 voltages as they are believed to be more realistic. Table 3-9 includes the following data:
- 1) Two sets of growth data for the first cycle of operation after deplugged tubes are returned to service.
- 2) Growth rates for two consecutive cycles of operation for deplugged tubes retumed to service.
Deplugged tubes mturned to service in SG-B for Cycle 11 operation and those returned to service in SG-A for Cycle 12 operation had higher growth rates than the tubes active in the prior cycle, although the absolute growth b small for all SGs. On the basis of composite data from all SGs, deplugged tubes returned to service for Cycle 11 operation show a slightly higher growth rate (in comparison to active tubes) whereas the deplugged tubes returned to service for Cycle 12 operation do not show such an effect. Growth rates during the second cycle of operation for deplugged tubes returned to service during Cycle 11 are less than those for the corresponding )
active tubes. Thus, the data suggests that growth rate increase noted in the first cycle of operation (after the return to service) is temporary. No deplugged tubes were returned to service during the EOC-12 outage.
Table 3-10 lists the top 30 indications on the basis of Cycle 12 growth rates in descending order, and the data confirms that Cycle 12 had only modest growth. The growth values shown in this table are based on the adjusted EOC-11 voltages discussed above. All but 5 of the indications shown were RPC confirmed, but they are all below the 2 volt repair limit. Seven of the 30 indications shown are new indications, and EOC-11 voltages used to estimate growth rates for them were obtained by reevaluating the last inspection data; they are all relatively small indications.
Recently, some plants with 3/4" SG tubing experienced growth rates that demonstrated a potential dependency on the BOC voltages of previously identified indications. Such a growth )
behavior was observed after the repair limit for TSP indications was increased from 1 volt to 3 volts and, consequently, a significant number of indications with a BOC voltage between 1 volt I to 3 volts were left in service for the first time in the plant history.
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Large growths were observed primarily in indications with a BOC voltage over 1.5 volts. To l determine if Beaver Valley Unit-1 exhibited a similar trend, growth rate data for Cycle 12 (based on adjusted EOC-11 voltages) were plotted against BOC voltage, and the resulting plot is shown in Figure 3-7. It is evident fmm Figum 3-7 that Cycle 12 growth data do not show any
} trend to increase with BOC voltage. 'Ihe tmnd, if any, is for gmwth to decrease with BOC voltage; however, the growth rates are too small (negative average) to conclude that gmwth is decreasing with BOC voltage.
Assessment ofP6tential Guentive Factorsforlage Negative Gmwth in Cycle 12 l
l The extent of negative growth rates found for Cycle 12 is unusual for ARC applications and i potential contributing factors were reviewed. Since the negative growths are consistent across all SGs, the potential cause is judged to be independent of the SG inspected. Conceptual causes l would then be expected to relate to either a uniform difference in bobbin probes or the voltage l normalization technique applied to all SGs. Potential normalization issues could then be a problem in setting the voltage normalizations or a problem with the cross calibration of the standards to the reference laboratory calibration standard. The analysis setup of the voltage normalizations is always overchecked between the setups for the field and the voltage growth analyses. The voltage growth analyses yielded essentially the same bobbin voltages as the field analyses and the field voltage setup is not considered to be a contributor to the negative growths.
Different bobbin probes wem used in the two inspections. Zetec 720-ULC probes were used in the EOC-12 inspection and Westinghouse long life pmbes in the EOC-11 inspection. Both probes have been used extensively in field inspections with no apparent differences between the
, probes. As an additional check, both probes were compared by setting the reference voltage on l the 20% holes of a transfer standard and measuring the 20% hole voltages on another standard.
l No differences were found in the voltages and it is further concluded that the difference in i
probes does not significantly contribute to the negative growth rates. ,
I New ASME calibration standards were used in the EOC-12 inspection. These new standards were cross calibrated to the reference laboratory standard using the Beaver Valley transfer standard (standard cmss calibrated to the laboratory standard). The setup voltages for the 400/100 kHz mix were obtained by establishing the transfer standard to its cross calibrated value and measuring the mix voltage for each new standard. The resulting mix voltage for each standard was then used to normalize voltages for each standard in the bobbin coil field analyses.
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A different cross calibration procedure was applied for the ASME standards used in the EOC-11 inspection. For these standards, the setup voltages for the 400/100 kHz mix were obtained by:
establishing the transfer standard to its cross calibrated value at 400 kHz, measuring the 400 kHz voltage on the new standard and applying the Save/ Store option to obtain the 400/100 kHz mix voltage for the new standard. The resulting mix voltage for each standard was then used to normalize voltages for each standard in the bobbin coil field analyses as consistently applied in ARC inspections. These two calibration techniques are equivalent if the ratio of 400/100 to 400 kHz voltages are the same between the reference laboratory standard, the transfer standard and the new standard. To assess this difference between techniques, the bobbin data for the latter transfer and field standards were mevaluated based on setting all transfer and new standard voltages in the mix channel. It was found that the use of the 400 kHz cross calibration technique resulted in about 12.6% (up to 1.2% difference between standards) higher setup voltages for the mix channel than use of the 400/100 kHz cross calibration technique.
Based on the above, the bobbin voltages for the EOC-11 inspection are about 12.6% high.
Average growths were reevaluated for Cycles 11 and 12 based on reducing all EOC-11 voltages by 12.6%. When this adjustment is applied to all EOC-11 voltages, the negative Cycle 12 growth rate of -16.3% (Table 3-4) becomes about -3.8% (Table 3-6) and the Cycle 11 growth rate changes from 13.5% to about -0.9%. It is concluded that the reduced EOC-11 voltages represent an improved cross calibration to the laboratory standard and provide a better j representation of the growth rates. The growth rates for the last two cycles at Beaver Valley-1 show very small growth which is consistent with the 3% growth seen for Cycle 10 (Table 3-7).
Similar differences were found between the two cross calibration techniques when additional standards were evaluated. It appears that the reference laboratory standard has a higher ratio of 400/100 to 400 kHz voltages than typical of many other standards. Since voltages in the ARC database are based on mix voltages traceable to the reference laboratory calibration standard mix voltage, the most appropriate cross calibration procedure is to setup all voltages on transfer and 1 new standards in the mix channel.
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3.3 NDE Uncedainties The non-destructive examination (NDE) uncertainties applied for the Cycle 12 voltage distributions in the Monte Carlo analyses for leak rate and burst probabilities are the same as those previously mported in the Beaver Valley Unit-1 voltage-based repair criteria report of Reference 8-2 and NRC Generic Ietter 95-05 (Reference 8-1). 'Ihe probe wear uncertainty has
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E a standard deviation of 7.0 % about a mean of zem and has a cutoff at 15% based on implementation of the probe wear standard. If the random sample of probe wear selected dering the Monte Carlo simulations exceed 15%, sampling of the probe wear distiibution is continued until a value less than 15% is-picked. De analyst variability uncertaimy has a standard deviation of 10.3% about a mean of zero with no cutoff. Dese NDE uncertainty distributions are included in the Monte Carlo analyses for SLB leak rates and tube burst probabilities based on the EOC-12 actual voltage distributions as well as for the EOC-13 projections. In the EOC-13 projection analysis, NDE micertainty adjustment is applied to the BOC voltage before growth is added to obtain EOC voltage.
3.4 Probability of Prior Cycle Detection (POPCD) l The inspection results at EOC-12 permit an evaluation of the pmbability of detection at the prior EOC-ll inspection. For voltage-based repair criteria 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 of interest for voltage-based repair criteria 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.
1 EOC-12 RPC confirmed + Indications confirmed and indications reported in EOC-11 repaired in EOC-11 l
inspection inspection
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l (EOC-11) { Numerator} + New indications RPC confirmed in EOC-12 inspection POPCD is evaluated at the 1996 EOC-11 voltage values (fmm 1997 reevaluation for growth
- rate) since it is an EOC-11 POPCD assessment. The indications detected at EOC-11 that were j RPC confirmed and plugged are included as it can be expected that these indications would also l have been dateted and confirmed at EOC-12. It is also appropriate to include the plugged tubes for voltage-based repair criteria applications since POD adjustments to define the BOC distribution are applied prior to reduction of the EOC indication distribution for plugged tubes.
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-Il below detectable levels and l l indications that initiated during Cycle 12. Thus, this definition, by including newly initiated indications, differs from the traditional POD definition.
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Since the newly initiated indications are appropriate for voltage-based repair criteria applications, POPCD is an acceptable definition and eliminates the need to adjust the traditional POD for new indications.
l 'Ihe above definition for POPCD would be entirely appropriate if all EOC-12 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 l inspected would have been RPC confirmed. This definition is applied only for the 1997 EOC-12 l
indications not RPC inspected since inclusion for the EOC-11 inspection could increase POPCD by including indications on a tube plugged for non-ODSCC causes which could have RPC NDD
, indication. In addition, the objective of using RPC confirmation for POPCD is to distinguish i detection ofindications at EOC,3 that could contribute to burst at EOC, so that the emphasis is on EOC, 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 Beaver Valley Unit-1.
l The POPCD evaluation for the 1996 EOC-11 inspection data is shown on Figure 3-8 and {
summarized in Table 3-11. Since there are only 3 indications in 2 to 2.5 volts bin, they were l combined with those in 1.5 to 2 volts bin in Figure 3-8. A generic POPCD distribution l l developed by analyzing data from 15 inspections in 8 plants, presented in Table 7-4 of Reference 8-4, is also shown in Figure 3-8. For voltages above about 0.6 volt, EOC-11 POPCD values are substantially higher than the NRC mandated POD value of 0.6, and they remain above 0.90 beyond 0.8 volt.
In summary, the Beaver Valley Unit-1 EOC-Il POPCD strongly supports a voltage dependent l POD substantially higher than the NRC mandated POD value of 0.6 above about 0.6 volts and approaching unity at about 2.5 volts, and it is in good agreement with the generic POPCD distribution presented in Reference 8-4 3.5 Assessment of RPC Confinnation Rates This section tracks the 1996 EOC-11 indications left in service at BOC-12 relative to RPC inspection results in 1997 at EOC-12. Composite results for all SGs are given in Table 3-12.
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 1997. Also included are new 1997 indications. The table shows, for each category of indications, the number of indications RPC inspected and RPC confirmed in 1997 as well as the percentage of RPC confirmed indications.
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Out of a total of 35 RPC NDD indications from all three SGs left in service in 1996,11 were RPC tested in 1997 and 3 of those were confirmed. Thus, the overall RPC confirmation rate for 1996 RPC NDD indications is 27.3 %. This overall confirmation rate is significantly below that found for RPC NDD indications tested in last two inspections. (60% in 1996 and 50.9% in 1995), and it is the same as that found for 1991 RPC NDD indications RPC tested in 1993 (27.2%). For successive ARC inspections at other plants, the confirmation rate for RPC NDD indications left in service was typically < 40%.
The NRC Safety Evaluation Report (SER) for Beaver Valley-1 (Reference 8-5) allows for consideration of only a fraction of RPC NDD indications fmm the current inspection in establishing the BOC voltage distribution for the next cycle. The fractional value applicable is the largest RPC confirmation rate for prior cycle RPC NDD indications found during the last two outages, but it may not be less than 0.7. Thus, the fraction that can be applied for 1996 RPC NDD indications is 0.7.
3.6 Probe Wear Criteria l An alternate probe wear criteria approved by the NRC (Reference 8-6) was applied during the EOC-12 inspection. When a probe does not pass the 15% wear limit, this alternate criteria requires that only tubes with indications above 75% of the repair limit inspected since the last ,
successful probe wear check be reinspected with a good probe. As the repair limit for Beaver Valley Unit-1 is 2 volts, all tubes containing indications for which the worn probe voltage is above 1.5 volts are to be inspected with a new probe. A total of 13 indications with a bobbin voltage above 1.5 volts were found in the calibration groups that failed probe wear checks, and the tubes containing those indications were reinspected with a new probe (Reference 8-7). No new indications were indicated during reinspection with a new probe, and no indications had its voltage increase above the repair limit when reinspected with a good probe. For indications with a worn probe voltage above 1.5 volts, the average difference between the worn and new probe voltages was only -0.09 volt.
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As required by Referec.cc 8-6, the number of new indications detected in the present inspection in tubes which were inspected with a wom probe in the last inspection was also determined. Out of a total of 624 new indications found in the current inspection, only 61 are in tubes inspected with a worn probe in the last inspection, which is not considered a disproportionate number of
, indications since they were found in a tube population making up 10 calibration groups. Also, actual indication population distributions from the current inspection were compared against the projected distributions based on the prior cycle data presented in Reference 8-2, and the projections were found to be conservative (see Section 6.0 for details). Thus, the requirements specified in Reference 8-6 for applying the alternate probe wear criteria are met.
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3-10
l Table 3-1
- Beaver Valley Unit-1 October 97 Outage Summary ofInspection and Repair For Tubes in Service During Cycle 12 l Steam Generator A Steam Generator B l In-service Dunng Cycle Cycle - 13 In Service Dunng Cycle Cycle 13 Voltage All Tubes All Tubes Bin RPC RPC Indications Returned RPC RPC Indicauons Returned g
Inspected Confirmed Repared to inspected Confirmed Repaired to Indications Service Semce 0.1 0 0 0 0 0 1 1 I O I
_2 _ _ _ _ _
1
_ .. ._ I __ _5 ,_ .._3 _ _ 38 0.5 205 26 15 9 1% 134 19 12 7 127 l 0.6 159 33 22 4 154 120 9 7 5 115 i 0.7 138 22 15 2 137 93 17 13 1 92 l 0.8 78 40 33 77 57 29 26 2 1 55 0.9 80 64 55 1 79 41 34 30 0 41 1 45 40 36 3 42 26 26 25 1 25 1.1 31 31 25 2 29 25 25 23 0 25 l 1.2 23 23 22 1 22 20 18 16 0 20
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> lv 121 118 106 13 108 74 72 66 0 74
> 2v 3 3 3 3 0 0 0 0 0 0 l
l Steam Generator C Composite of All Steam Generators in-Service Dunng Cycle Cycle 13 In Service Dunns Cycle Cycle - 13
( Voltage AllTubes All Tubes l B'n RPC RPC Indications Returned RPC RPC Indications Returned g
inspected Confirmed Repaired to inspected Confinned Repaired to I Indications , ,
Service Service 0.1 0 0 0 0 0 1 I, I. O g i
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Table 3-7 Beaver Valley Unit-1 October 1997 Average Voltage Growth for Cycle 12 l Composite of All Steam Generator Data )
(Based on Unadjusted EOC-11 Voltages) '
Bobbin Voltage Number of Average Voltage Average Voltage Gnmth Average Perrentage Gnmth i
l Range Indications BOC Entire Cycle Per EFPY Entire Cycle Per EFPY Cycle 12 (1996 - 1997) - 415.4 EFPD Entire Voltage Range 2910 0.68 -0.111 -0.098 -16.3% -14.4%
V nce < .75 Volts 1904 0.48 -0.076 -0.067 15.8 % -13.9%
2.75 Volts 1006 1.06 -0.178 0.157 -16.8% -14.8%
Cycle iI (1995 - 1996) - 352.94 EFPD Entire Voltage Range 1936 0.60 0.080 0.083 13.5 % 13.9 %
V noce .75 Vola 1434 0.48 0.076 0.078 15.9 % 16.5 %
2.75 Voits 502 0.94 0.093 0.096 9.9% 10.2 %
Cycle 10 (1993 - 1995) - 435.79 EFPD Entire Voltage Range 1089 0.66 0.020 0.017 3.0% 2.5%
V noe < .75 Volts 751 0.50 0.040 0.034 8.0% 6.7%
2.75 Volts 338 1.01 -0.010 -0.008 -1.0% -0.8%
Cycle 9 (1991 - 1993) - 492.75 EFPD Entire Voltage Range 1125 0.57 0.090 0.067 15.8 % 11.7 %
918 0.47 0.090 0.067 19.1 % 14.2 %
_ V noe < .75 Volts 2.75 Volts 207 1.02 0.090 0.067 8.8% 6.5%
Cycle 8 (1989 - 1991) - 390.82 EFPD Entire Voltage Range 952 0.95 0.180 0.168 18.9 % 17.7 %
V noc < .75 Volts 366 0.58 0.160 0.150 27.6 % 25.8 %
2.75 Volts $86 1.18 0.190 0.178 16.1 % 15.0 %
Cycle 7 (1987 - 1989) - 438.3 EFPD Entire Voltage Range 918 0.66 0.290 0.242 43 9 % 36.6 %
V noc < .75 Volts 622 0.49 0.270 0.225 55.1% 45.9%
2.75 Volts 296 1.01 0.340 1 0.283 33.7 % 28.1%
I l
l 3-17 i% ,iceuw . .
l l
Table 3-8 Beaver Valley Unit-1 October 1997 Voltage Growth Statistics - Composite of All Steam Generator Data (Based on EOC-ll Bobbin Voltages Multiplied by 0.8'/4 for Calibration Adjustment)
Bobbin Voltage Number of Average Voltage Average Voltage Growth Average Percentage Growth Range Indications BOC Entire Cycle Per EFPY Entire Cycle Per EFPY Cycle 12 (1996 - 1997) - 415.4 EFPD Entire Voltage Range 2910 0.60 0.025 -0.022 -4.3% -3.8%
l V w < .75 Volts 2181 0.46 -0.020 -0.017 -4.4% -3.8%
2.75 Volts 729 1.01 -0.042 -0.037 -4.1% -3.6%
, Cycle 11 (1995 - 1996) - 352.94 EFPD l
l Entire Voltage Range 1936 0.60 -0.005 -0.005 -0.8% -0.9%
V noc < .75 Volts 1434 0.48 0.006 0.007 1.3% 1.4%
2.75 Volts 502 0.94 -0.037 -0.038 -4.0% -4.1%
l Cycle 10 (1993 - 1995) - 435.79 EFPD l Entire Voltage Range 1089 0.66 0.020 0.017 3.0% 2. ',%
V noc < .75 Volts 751 0.50 0.040 0.034 8.0% 6.7%
2.75 Volts 338 1.01 -0.010 -0.008 -1.0% -0.8%
Cycle 9 (1991 - 1993) - 492.75 EFPD
! Entire Voltage Range 1125 0.57 0.090 0.067 15.8 % 11.7 %
V noc < .75 Volts 918 0.47 0.090 0.067 19.1 % 14.2 %
i 2.75 Volts 207 1.02 0.090 0.067 8.8% 6.5%
Cycle 8 (1989 - 1991) - 390.82 EFPD Entire Voltage Range 952 0.95 0.180 0.168 18.9 % 17.7 %
l V noc < .75 Volts 366 0.58 0.160 0.150 27.6 % 25.8 %
2.75 Volts 586 1.18 0.190 0.178 16.1 % 15.0 %
l Cycle 7 (1987 - 1989) - 438.3 EFPD Entire Voltage Range 918 0.66 0.290 0.242 43.9 % 36.6 %
l V ax.< .75 Volts 622 0.49 0.270 0.225 55.1 % 45.9%
2.75 Volts 296 1.01 0.340 0.283 33.7 % 28.1 %
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Table 3-10 Beaver Valley Unit-1 October 1997 Summary of Largest Voltage Growth Rates for BOC-12 to EOC-12 (Based on EOC-11 Bobbin Voltages Multiplied by 0.874 for Calibration Adjustment)
Steam Generator Bobbin Voltage RPC New SG Row Col Elevation EOC BOC Growth" Confirmed ? Indication ?
A 28 60 OlH 1.61 0.65 0.96 Y N A 31 62 OlH 1.51 0.68 0.83 Y N C 29 22 OlH 1.21 0.76 0.45 Y N A 20 11 02H 0.78 0.39 0.39 Y Y A 25 78 04H 1.06 0.68 0.38 Y N A 18 78 0111 0.97 0.6 0.37 Y N B 14 81 0;n 1.2 0.84 0.36 Y Y A 5 19 02H 0.97 0.63 0.34 Y Y A_ 8_ _ 84 03H 0.55 _ _0_.23 _ 0.32 N Y A_ _ _ 31 68 02H _l .37__ _ _. 1._07 _ _0.3 _ _ . _
Y N
__.A.. 6_ 12 OlH _ _ l .68 _ _ 1 39 _ _ 0.29 _ _ . _
Y _ _
N
. B._ 15 26 02H ._ 0.76_ _0._47 ._ _ 0.29_ _ __Y N
_A _ _ 31 _ _ 42 OlH 1.11_ 0.83 _ _ 0.28 _ _ _ Y_ _
N A 21 75 02H 0.44 0.17 0.27 N Y A 33 30 OlH 1.42 1.15 0.27 Y N A 35 35 OlH 1.03 0.76 0.27 Y Y C 21 22 OlH 1.42 1.16 0.26 Y N A 26 11 OlH 1.48 1.23 0.25 Y N C 38 32 OlH 0.91 0.66 0.25 N N A- 6 18 03H 0.74 0.5 0.24 Y N A 35 35 02H 1.55 1.31 0.24 Y N l A 17 14 OlH 1.05 0.82 0.23 Y Y !
A 23 23 OlH 0.9 0.67 0.23 Y N B 8 82 02H 0.69 0.47 0.22 N Y C 15 62 02H 0.98 0.76 0.22 Y N C 24 28 OlH 1.16 0.94 0.22 Y N C ._ 32 _ 24 02H _0.73 _ 0.51 _ 0.22 Y N C_ _ 33 68 OlH _ l .15_ _0.9_3 0.22 _
Y N A_ 23 47 OlH _ 0.52 _ 0.31 0.21 N N A 7 8 OlH 1.2 0.99 0.21 Y N
- Based on EOC-11 voltages adjusted for calibration differences.
Growth Table 310 3/29N8 6 42 PM 3-20
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l 4.0 Database Applied for Leak and Burst Correlations l
The leak and burst correlations utilized in the analyses presented in this report are based on an updated ARC database. The database protocol submitted to the NRC in the Fall of 1997 indicates that the database should be updated if "...the inclusion of new data results in a non-conservative shift in the correlation predictions..." Inclusion of recent pulled tube data l from Plans A-1 and A-2 makes the leak and burst correlations less conservative. So, as an
! interim update of the database, Plants A-1 and A-2 data were added to the Reference 8-4 database and leak and burst correlations were reevaluated. The parameters of the updated leak and burst correlations are presented in Reference 8-8. As required by the NRC, Model Boiler specimen 542-4 and Plant J-l pulled tube R8C74, TSP 1 are included in the database applied.
A leak rate correlation can now be applied to 7/8" tubes because NRC recently stated (Refemnce 8-10) that the p-value for the slope of the leak rate correlation determined on a one-sided basis (as opposed to a two-sided basis test used until now) can be used to test the l significance of the correlation. Reference 8-8 presents the results of a regression analysis for l the voltage dependent leak rate correlation using the updated leak rate database for 7/8" i tubes mentioned above, it is shown that the one-sided p-value for the slope parameter in
! the voltage dependent leak rate correlation is 3.8% which is below the 5% threshold for an l acceptable correlation specified in the Generic Letter 95-05. Thus, the leak rate database for 7/8" tubes now satisfies the statistical test for a correlation.
The following leak rate correlation is developed in Reference 8-8 for 7/8" tubes based on an updated ARC database that includes the recent Plants A-1 and A-2 data.
l r 3
- 0.5036 + 0.9709 xlogw(volts)
Leak Rate (l/hr) = 10' >
l The above leak rate cormlation was used to perform EOC-13 SLB leak rate projections for all three SGs .
l I
l l
1 l
S:\ arc \div97\ Cycle 13.90d. doc 4-1 j
5.0 SLB Analysis Methods Monte Carlo analyses are used to calculate the SLB leak rates and tube burst probabilities for both actual EOC-12 and projected EOC-13 voltage distributions. The Monte Carlo analysis accounts for parameter uncertainty. The analysis methodology is described in the Westinghouse .
generic methods report of Reference 8-3, and the same methodology was applied to leak and l burst analyses performed during the EOC-11 outage.
I I
In general, the methodology involves application of correlations for burst pressure, probability ofleakage and leak rate to a measured or calculated EOC distribution to estimate the likelihood of tube burst and primary-to-secondary leakage during a postulated SLB event. Uncertainties associated with burst pressure, leak rate probability and leak rate correlations are explicitly included by sampling distributions for the correlation parameters through a Monte Carlo sampling process. NDE uncertainties are also similarly included. The voltage distributions used in the leak and burst projections for the next operating cycle are obtained by applying growth data to the BOC distribution. The BOC voltage distributions include an adjustment for detection uncertainty and occurrence of new indications, in addition to the adjustments for NDE uncertainties. Comparisons of projected EOC voltage distributions with actual distributions after a cycle of operation have shown that the Monte Carlo analysis technique yields conservative estimates for EOC voltage distribution as well as leak and burst results based on those distributions.
Equation 3.5 in Reference 8-3 was used to determine the true BOC voltage. The method of treating fractional indications is discussed in Section 3.6 of Reference 8-3. Fractional indications in the EOC voltage bins are retained, and the tail of the distribution is integrated to define discrete values corresponding to the last 1/3"' and 2/3"' of an indication.
l l
5:\ ape \dlw97\Cyclel3_90d. doc 5-1
)
O l
l
! 6.0 Bobbin Voltage Distributions l
This section describes the salient input data used to calculate EOC bobbin voltage distributions and presents results of calculations to project EOC-13 voltage distributions. Also, EOC-12 voltage projections perfunici during the last outage based on EOC-11 inspection bobbin voltage data are compared with the actual bobbin distributions from the current inspection.
l 6.1 Calculation of Voltage Distributions The analysis for EOC voltage distribution starts with a cycle initial voltage distribution which is projected to the end of cycle conditions based on the gmwth rate and the anticipated cycle operating period. The number of indications assumed in the analysis to project EOC voltage distributions, SLB leak rates and tube burst probabilities is obtained by adjusting the number of l reported indications to account for detection uncertainty and birth of new indications over the I projection period. This is accomplished by using a POD factor, which is defined as the ratio of the actual number of indications W~i to total number of indications present. A conservative value is assigned to POD based on historic data, and the value used herein is discussed in Section 6.2. The calculation of projected bobbin voltage frequency distribution is based on a net total number ofindications returned to service, defined as follows.
Nr,gn = N,/ POD - N g +N w where, l Nr.rm = Number of bobbin indications being returned to service for the l next cycle, N, =
Number of bobbin indications (in tubes in service) identified after the previous cycle, POD = Probability of detection, Ng = Number of N, which are repaired (plugged) after the last cycle, Nw = Number of indications in tubes deplugged after the last cycle and returned to service in accordance with voltage-based repair criteria.
There are no deplugged tubes returned to service at BOC-13; therefore, Nw = 0.
S:\apc\ ten 97\cyclel3_90d. doc 6-1
s As noted in Section 3-4, the NRC SER for Beaver Valley-1 allows for consideration of only a fraction of RPC NDD indications from the current inspection in establishing BOC voltage distribution for the next cycle. De fractional value applicable is the largest RPC confirmation rate for prior cycle RPC NDD indications found during the last two outages, but it may not be less than 0.7. RPC confirmation rates for 1995 and 1996 RPC NDD indications are well below 0.7; therefore, only 70% of RPC NDD indication frequency values are considered in establishing the BOC-13 indication distributions shown in Table 6-2. During the Monte Carlo l simulations, voltages for bins with 3 or more indications are selected by randomly sampling the l voltage bins. For bins with fewer than 3 indications, each indication is considered to be in a l separate bin, and the actual indication voltage is utilized in the calculations.
i
! The methodology used in the projection of EOC bobbin voltage frequency predictions is described in Reference 8-3, and it is the same as that used in performing EOC-12 predictions during the last (EOC-11) outage (Reference 8-2). Salient input data used for projecting EOC-12 bobbin voltage frequency are further discussed below.
6.2 Probability of Detection (POD)
Generic Ixtter 95-05 (Reference 8-1) requires the application of a constant POD value of 0.6 to define the BOC distribution for EOC voltage projections, unless an alternate POD is approved by the NRC. A POD value of 1.0 represents the ideal situation whem all indications are !
detected. A voltage-dependent POD provides a more accurate prediction of voltage distributions consistent with voltage based repair criteria experience. In this report both NRC mandated constant POD of 0.6 as well as a voltage %t POD developed for EPRI (POPCD) are used. The EPRI POPCD is developed by analyses of 15 inspections in 8 plants and is presented '
in Table 7-4 of Reference 8-4. The POPCD values applied represent the lower 95% confidence bound, and are reproduced in Table 6-1 as well as graphically illustrated in Figure 6-1.
6.3 Limiting Growth Rate Distribution As discussed in Section 3.2, the NRC guidelines in Generic Ietter 95-05 stipulate that the more conservative growth rate distributions fium the past two inspections should be utilized for projecting EOC distributions for the next cycle. It is evident from Figure 3-6 that growth rates for Cycle 11 on an EFPY basis are higher than those of Cycle 12; therefore, the Cycle 11 growth rate distribution is used to develop EOC-13 predictions. Cycle 11 growth rates for SG-B are slightly higher than the all SG composite growth distribution and, per the methodology S:\apc\ ten 97\Cyclel3 90d. doc 6-2
n l
described in Reference 8-3, SG-specific growth rates are to be used for SG-B while the composite gmwth rates should be applied for the other two SGs. Although Cycle 11 growth rates shown in Table 3-3 are believed to be overestimated as they are based on unadjusted EOC-11 voltages (see Section 3.2), they were applied to obtain conservative EOC-13 predictions.
l Gmwth distributions used in the Monte Carlo calculations are specified in the form of a histogram, so no interpolation is performed between growth bins. This assures that the largest l growth value in the distribution is utilized in the Monte Carlo simulations. #
6.4 Cycle Operating PMod l The operating periods used in the growth rate /EFPY calculations and voltage projections are as '
- follows. ;
Cycle 12 -
BOC-12 to EOC-12 - 415.4 EFPD or 1.14 EFPY (actual)
Cycle 13 - BOC-13 to EOC-13 - 500 EFPD or 1.48 EFPY (projected)
}
6.5 Projected EOC-13 Voltage Distribution Calculations for EOC-13 bobbin voltage pmjections were performed for all three SGs based on l the EOC-12 distributions shown in Table 6-2. The BOC distributions were adjusted to account for pmbability of detection as described above, and the adjusted number of indications at BOC-13 are also shown in Table 6-2. Calculations were performed using a constant POD of 0.6 as j well as the EPRI POPCD distribution (presented in Table 6-1). The total number of EOC-13 indications pmdicted with EPRI POPCD for SGs B and C are slightly higher than those based on the POD value of 0.6. 'Ihe reason for this being that about half of the indication population at EOC-12 is below 0.5 volt and the EPRI POPCD value for such indications is less than 0.6.
The larger growth rates for the last two cycles of operation, which am the Cycle 11 gmwth rates shown in Table 3-3, were applied. As noted in Section 3.2, growth values shown in Table 3-3 are believed to be overestimated; they were used nevertheless to obtain conservative EOC-13 predictions. 'Ihe EOC-13 voltage distributions thus projected for all three SGs are summarized on Table 6-3. These results are also shown graphically on Figures 6-2 to 6-4. In general, the results based on a constant POD of 0.6 are slightly more conservative (slightly larger maximum EOC voltage) than those using the voltage %t EPRI POPCD.
I S:\apc\ ten 97\cyclel3,90d. doc 6-3
I
\
6.6 Comparison of Actual and Pmjected EOC-12 Voltage Distributions Table 6-4 and Figure 6-5 provide a comparison of the EOC-12 actual measured bobbin voltage distributions with the corresponding projections performed using the last (EOC-11) inspection bobbin voltage data and presented in Reference 8-2. The EOC-12 projections shown are based on a constant POD of 0.6. As predicted in Reference 8-2, SG-A has the largest number of indications; however, while SG-B was predicted to have the largest indication, SG-A had the largest actual measured bobbin voltage. The actual peak voltages measured are 0.4 to 1.9 volts below their projected values, with the voltage difference being the highest for SG-B (1.9 volts).
A comparison of the actual and projected voltage distributions in Figure 6-5 show that the indication population above 0.6 volt is substantially overestimated in the projections based on a constant POD of 0.6. His POD value is conservative for voltages above about 0.5 volt but non-conservative below 0.5 volt as seen in Figure 6-1. As seen in the results for SG-B in Figure 6-5, the projections based on POPCD show better agreement with the actual voltages, while remaining a conservative projection, over the entire voltage range than found for POD =0.6 S:\eps\ ten 97\Cyclel3_90d. doc 6-4
I l
t Table 6-1 EPRI POPCD Distribution Based on Data from 15 Inspections in 8 Plants Voltage EPRIPOPCD*
Bin
_ _.._ _ 0.1 _ _ _ _ _ _._ _ _0.24 . _
0.2 0.34 0.3 0.44 0.4 0.53
_..._. _ 0.5 _ _ _ _ _ 0.6_2 .
0.6 ._ ._
_ ___ _ 0.67_ _ _ _ _
._ . _ _ _ 0 7 __
_ _ _ __ _ _, _ 0.73 __
- 0. 8 _ __ ____ _ . 0_.77 _
_. ._._ 0.9 _ . _._ . _ _0.81 ._
1
_ . _ _ . _ . . . _ _ 0._83 1.2 _ _ . _ _ __ _ _ __ _._ _ _0. 8 8 1.4 0.91 1.6 _ . _ _ _
0.92 1.8 _ _ __ _ _ _0 93 __
2 _. _ . _ _ _ ._ _ _ _ . 0.94 _ _ _
__ . _ 0. 8
- Data from Table 7-4 in Reference 8-4.
{
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Table 6-3 Beaver Valley Unit-1 October 1997 Predicted Voltage Distributions for EOC-13 Steam Generator A l Steam Generator B Steam Generator C Voltage Projected Number ofIndications at EOC-13 Bin POD EPRI POD EPRI POD EPRI 0.6 POPCD 0.6 POPCD 0.6 POPCD 0.1 0.77 1.37 0.62 1.25 0.95 1.68 0.2 18.86 31.37 10.41 17.79 20.21 34.30 0.3 73.36 105.72 44.40 66.51 57.49 87.13 0.4 156.80 200.82 102.58 137.30 99.43 133.24 0.5 230.80 268.40 157.64 193.26 134.16 160.94 0.6 264.54 282.76 188.34 214.45 152.64 165.47 0.7 257.72 255.17 193.71 204.50 149.46 148.73 0.8 226.96 210.02 175.98 172.93 130.99 121.88 0.9 186.38 162.98 146.72 135.72 107.78 94.63 1.0 146.69 121.98 116.77 102.76 85.71 71.43 1.1 111.46 88.67 90.08 75.72 67.14 53.35 1.2 82.57 63.10 67.96 54.58 52.43 39.94 1.3 60.45 44.51 50.65 39.00 41.27 30.27 1.4 44.33 31.57 37.57 28.06 32.71 23.27 1.5 32.75 22.66 27.56 20.11 25.76 17.92 1.6 24.36 16.44 19.83 14.14 19.91 13.58 1.7 18.19 11.99 14.06 9.82 14.88 10.04 1.8 13.53 8.75 9.84 6.76 10.70 7.15 1.9 9.92 6.34 6.77 4.58 7.41 4.93 2.0 7.13 4.50 4.55 3.05 4.97 3.28 2.1 5.00 3.12 2.97 1.98 3.24 2.13 2.2 3.41 2.08 1.89 1.25 2.05 1.35 2.3 2.27 1.35 1.17 0.77 1.27 0.83 2.4 1.49 0.84 0.60 0.05 0.76 0.14 2.5 0.98 0.21 0.00 0.70 0.00 0.70 2.6 0.65 0.00 0.70 0.00 0.70 0.00 2.7 0.36 0.70 0.30 0.30 0.00 0.30 2.8 0.00 0.30 0.00 0.00 0.30 0.00 2.9 0.70 0.00 0.00 0.00 0.00 0.00 3.1 0.30 0.00 0.00 0.00 0.00 0.00 TOTAL 1982.73 1947.72 1473.67 1507.34 l 1224.32 1228.61
>1V 419.85 307.13 336.50 260.87 l 285.50 209.18
>2V 15.16 8.60 7.63 5.05 l 8.32 5.45 l
l l
I l
I Predaan,Tabhs 3 Legs 6 il PW 6-7 1
)
8 Tcbla 6-4 Beaver Valley Unit-1 October 1997 Comparison of Predicted and Actual EOC-12 Voltage Distributions i
Steam Generator A Steam Generator B Steam Generator C Prediction Prediction Prediction Voltage Actual Actual Actual Bin POD = 0.6 POD = 0.6 POD = 0.6 0.1 0.08 0 0.16 1 0.07 0 0.2 4.74 43 6.68 41 3.62 54
~ ~~
0.3 38.73 144 22.88 137 23.63 96 0.4 96.80 228 50.63 189 53.37 108 j 0.5 _,
149.47 205 86.03 134 77.51 117 0.6 181.66 159 114.88 120 96.28 105 0.7 188.64 138 131.61 93 104.88 67 l
~
0.8 176.45 78 135.82 57 101.71 53 0.9 156.36 80 129.58 41 91.26 35 1.0 132.49- . - . - .
45 116.75 26 77.29 35 1.1 106.03 31 100.34 25 62.32 16 1.2 80.22 23 82.66 20 48.36 22 1.3 58.13 22 65.81 10 36.79 15 1.4 41.12 8 51.07 6 27.87 11 1.5 29.06 14 38.91 5 21.19 12 1.6 20.92 7 29.26 4 16.25 5 l 1.7 15.35 6 21.70 3 12.45 2 l 1.8 11.38 3 15.86 1 9.43 1 1.9 8.35 4 11.41 0 6.96 2 2.0 5.96 0 7.99 0 4.96 0
! 2.1 4.13 1 5.48 0 3 0 l 2.2 2.77 0 3.66 0 2 0 2.3 1.79 0 2.37 0 1.43 0 2.4 1.14 0 1.49 0 0.88 0 l
2.5 0.71 2 0.91 0 0.21 0 2.6 0.04 0 0.54 0 0.70 0 2.7 0.70 0 0.32 0 0.00 0
, 2.8 0.00 0 0.05 0 0.30 0 2.9 0.30 0 0.00 0 0 0 3.1 0 0 0.70 0 0 0 3.7 0 0 0.30 0 0 0 TOTAL 1513.50 1241 1235.83 913 885.33 756
>1V 388.10 121 440.81 74 255.73 86
>2V 11.58 3 15.81 0 9.15 0 Prodcomp Predcomp 1/31/98 5:48 PM gg
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Figure 6-2 Ileaver Valley Unit 1 - SG-A l Predicted Bobbin Voltage Distribution for Cycle 13 l POD = 0.6 400 350 300 -
O BOC-13 E -
g 250 - - _
f M Predicted EOC-13 h200 o
3 150 Z
100- - - - - - -
so _ ._ - - _ _ _
0- - -
- ' #E " " - - --
- a
- :::::::::::::::::::::::::;
Bobbin Voltsge POD = EPRI POPCD 450 400 350 O BOC 13 g 300 _ _
o j E Predicted EOC-13 g 250 -- - - --
1 S i 15 l 200 -- - - - -
l Z 150- - - - - - -
l l
300 .._. _ _ _ .
so .._ .. _ _ _ _.
0
^ " :~-- -
Bobbin Voltage
- , , , , - . , , ~
6-10
Figure 6-3 Ileaver Valley Unit-1 -- SG-il Predicted Bobbin Voltage Distribution for Cycle 13 POD = 0.6 350 300 O BOC-13 250 e
s n ,00 "_ _
A Predicted EOC-13 S
o j 150 - - - - -- -
5 z
100 - - - - - -
50 - ---- - - - - - - - -
0
- M. _
.__E. m. . _. _ _ . _
a: : : : : : : : : : : : : :
Bobbin Voltage e
O BOC-13 250 -
E o
j E Predicted EOC-13 o 200 - - -- -
o jSo _ _ _. _ _
100 - - - - - - - -
50 - - - - - - -- -- - -
, ~
-N I
q
- m e > e e o e N
.r n
! I LL. . _.e e. o_ _ -.
w m e N e q q v m I
8 j o o o o o o o o o e e e - - e - e e - n n u n n n n I Bobbin Voltage
-o vm.. m 6-11
e Figure 6-4 Beaver Valley Unit SG-C Predicted Bobbin Voltage Distribution for Cycle 13 POD = 0.6 200 180 -
0 00C-13 160 - -
l l
140 - - - -
f W Predicted EOC-13 i120 - - - - -
~
100 - - - - - -
E so ,__ .__. _ - _ _ _
i 60 - - - - - -
40 - - - - - - - - - -
l 20 - - - - - - - - - - -
0 SSX1. ._ _
5 $$5$$$$$3 2 U U Bobbin Voltage U $ $ U U $;NOU$$
200 O BOC-13 E
o 3 ~
150 f5 M Predicted EOC-13 a
100 -- - - - - -
~
so _ _ ._ _ _ _ _ _ _
0
' ' ^
^^ "^ - ^ - - --
- ; ; ;
- : : : : : : : : : : : : =;=;;
Bobbin Voltage wo vm. '
- 6-12
Figure 6-5 Beaver Vaticy Unit-1 October 1997 Hobbin Voltage IXstributions for Cycle 12 Steam 250 200 -
D Mtul 50 - -. - - -
a Fredkted rop - e.s J
1 00 _ .__ _ _ _ _ _ _
r.
50 - - - - - - - - - -
0 ": : :" : : : :'I 'E : ':* - - --
01020.3040506070809 1 1.11.21.31415161.71819 2 21222.32425262729 nom vomane Steams Generator B 200 '
l 180 auw l 160 !
j 140 m Frasktni son.o.s l 120 - - --
a l . s er.aut.a rorco 1 100 - - -
, l 1- 60 g
l l !
l l l c
l l l
40 . - _ . . _ _.
3 ! ! ! ~
! } "I a l l l l l l J 20 --- - 1 :l l l l '
l l -
0- E i M'"~--
0.102030405060.70809 1 1.11.2131415161.71819 2 2.1222324252627283137 sata n vokase Steam Generator C 140 120 100 - - - -
D uumi a rredkted rop - o.s C 80 -- - - - - -
}
60 - - - - - - -
40 _. _. _ _ _ _ _ _ -
20 - - - - - - - - - - --
0 .;
-JIJilll14.(..,_;_.. .
l 010.203040506070809 1 11121.3141516171819 2 21222324252628 m<dMa Voltage urmisy als Fu_6 49M 13 89 AM b!3
{
j 7.0 SLB Imak Rate and Tube Burst Probability Analyses This section presents the results of analyses carried out to predict leak rates and tube burst probabilities for postulated SLB conditions using the actual voltage distributions from the EOC-12 inspection as well as for the projected EOC-13 voltage distributions. ne methodology used in these analyses is described in Section 5.0. SG-A with the largest total number of indications as well as indications over 1 volt is expected to yield the limiting SLB leak rate and burst probability l for Cycle 13.
I 7.1 leak Rate and Tube Burst Probability for EOC-12 l
! Analyses to calculate EOC-12 SLB leak rates and tube burst probabilities were performed using the actual bobbin voltage distributions presented in Table 6-2. Results of Monte Carlo calculations am summarized on Table 7-1. A comparison of the EOC-12 actuals in Table 7-1 with the corresponding predictions performed during the EOC-11 inspection, presented in Reference 8-2, indicates the following.
l i a) Total number of indications found in the EOC-12 inspection for all three SGs are well l below their projection based on POD =0.6. De peak measumd voltage for all SGs are l 0.4 to 1.9 volts below their projected values, with the voltage difference being the highest l for SG-B.
I b) leak rate and tube burst probability projections at EOC-12 are conservative compared to the corresponding values calculated using EOC-12 actual measumd bobbin measurements l for all SGs.
c) SG-B was predicted to be the limiting steam generator (slightly more conservative than l SG-A) at EOC-12 based on the SLB leak rate and tube burst probability projection i performed during the EOC-11 outage, but SG-A was found to have the highest leak rate and tube burst probability based on the actual EC bobbin measurements for EOC-12.
l d) Limiting values for SLB leak rate (2.4 gpm, without correlation; 0.3 gpm, with
! correlation) and tube burst probability (9.7 x 10 )5 obtained using the actual measured
! voltages are well below the allowable SLB leakage limit effective at EOC-12 (8.0 gpm, room temperature) and the NRC reportin;; guideline of 102 for the tube burst probability.
e) Leak rate and burst probability correlations used with the actual voltages are more conservative than those utilized for the projections. An additional calculation for SG-A performed using the same correlations applied for projections show a higher margin for the projection (see Table 7-1).
$$apcW97\ Cycle 13,,90d. doc 7-1
t In summary, actual measured EOC-12 bobbin voltage distributions for all SGs are well below the corresponding projections obtained using the NRC mandated probability of detection of 0.6.
7.2 I2ak Rate and Tube Burst Probability for EOC-13 Calculations to pnxiict SG leak rate and tube burst probability for the limiting steam genemtor in Beaver Valley Unit-1 at the EOC-13 condition were carried out using two values for POD: 1) ;
NRC required constant value of 0.6, 2) voltage dependent EPRI POPCD distribution. The methodology used for these predictions is the same as previously described for analysis based on EOC-12 actual voltages; however, a SG leak rate versus bobbin voltage conelation was applied as noted in Section 4.0. An updated leak rate and tube burst database that includes recent (1996 and 1997) data from plants A-1, A-2 and W-2 were used in the EOC-13 leak rate and tube burst probability projections. Projected results for EOC-13 conditions are summanzed on Table 7-2.
With a constant POD of 0.6, the limiting EOC-13 SG leak rate projected is 1.0 gpm (room temperature), and it is predicted for SG-A which has the largest number of indications as well as j the highest voltage indication retumed to service for Cycle 13 operation. This limiting leak rate value was calculated using a leak rate versus bobbin voltage correlation, and it is an order of magnitude below the allowable SG leakage limit of 8.0 gpm (room temperature) for Cycle 12.
d The limiting tube burst probability,1.6x10 , is also predicted for SG-A which had 10 of the 14 largest indications found in the EOC-12 inspxtion; it is nearly 2 orders of magnitude below the NRC reportmg guideline of 104 Table 7-2 also includes SG leak rates and tube burst probabilities calculated using the voltage dependent EPRI POPCD distribution. Application of the more realistic EPRI POPCD distribution to establish BOC-13 voltage distribution results in a reduction of SLB leak mte projections by about 25% and tube burst probability projections by about 50% relative to the projections based on a constant POD of 0.6. !
EOC-13 SG leak rates for all three SGs were also calculated using the methodology applied in the past in which leak rate is assumed to be independent of bobbin voltage, and these results are also shown in Table 7-2. It is evident that even the EOC-13 leak rates calculated with the old method remain below 50% of the allowable limit.
In summary, SG leak rates and tube burst probabilities predicted for EOC-13 are one to two decades below their respective allowable limits.
S:\spc\dlw97\ Cycle 13,,90d. doc 7-2
n o
Table 7-1 Beaver Valley Unit 1 1997 EOC-12 Outage Summary of Calculations of Tube leak Rate and Burst Probability Steam POD Number Max. Burst Probability Generator ofIndications Volts he 1 Tube 1 or More (gpm)
- Tubes EOC-12 PROJECTIONS (Based on ARC Database Pnsented in Reference 8-9)
A 0.6 1513.5* 2.9* 1.2 x 10-* l 1.2 x 104 4.3 B 0.6 1235.8* 3.7* 1.8 x 10
- 1.8 x 10 4.5 l
C 0.6 885.3* 2. 8* 1.0 x 10-
- 1.0 x 10-* 2.8 EOC - 12 ACTUALS (Based on ARC Database Updated to Include '96 Plant A-2 & '97 Plant A-1 Data) 9.7 x 10 5 9.7 x 10 5 2.4 A 1 1241 2.5 0.3W 3.1 x 10-'
- 3.1 x 10-5 m 3,9m 1.3 5
B 1 914 1.8 3.7 x 10 3.7 x 10-5 0.2W l
1 1.4 C 1 756 1.9 5.8 x 10- 5 5.8 x 10 5 0.2*
Notes: (1) Equivalent volumetric rate at room temperature.
(2) Adjusted for POD.
(3) Projected Maximum voltages include NDE uncertainties from Monte Carlo.
(4) Utilizes leak rate correlation based on an updated database including '% Farley-2,
'97 Farley-1 and '% Sequoyah-2 pulled tube exam data.
(5) Based on the database used for EOC-12 projections (presented in Reference 8-9).
Snapc\dlw97\cyclel3,90d. doc 7-3 i
he Table 7-2 Beaver Valley Unit-1 October 1997 Outage Summary of Projected Tube Leak Rate and Burst Probability for EOC 250k Simulations Steam No. of Max. Burst Probability SLB Generator POD Indic- Volts
- Leak ations* 1 Tube 1 or More Rate Tubes (gpm)*
EOC - 13 PROJECTIONS"*
(Leak Rate vs. Bobbin Voltage Correlation Applied) d A 0.6 1983 3.1 1.6x10 1.6x104 1.0 d
B 0.6 1474 2.7 1.1x10 1.1x10 4 0.7 C 0.6 1224 2.8 9.9x 10~5 9.9x 10-5 0.6 A POPCD 1948 2.8 7.8x10~5 7.8x10 5 0.7 B POPCD 1507 2.7 9.0x 10 5 9.5 x 10-5 0.6 C POPCD 1229 2.7 7.9x10 5 7.9x 10~5 0.5 EOC - 13 PROJECTIONS *'
(leak Rate Assumed Independent of Voltage)
A 0.6 1983 3.1 1.8x104 1.8x10 4 6.4 d
B 0.6 1474 2.7 1.2x10 1.2x 10" 4.9 C 0.6 1224 2.8 1.5x10d 1.5x 10" 4.1 Notes (1) Number ofindications adjusted for POD.
(2) Voltages include NDE uncertainties from Monte Carlo analyses.
(3) Equivalent volumetric rate at room temperature.
(4) 1.eak rate and burst probability correlations for 7/8" tubes presented in Reference 8-8 applied.
Database used includes 1996 Plants A-2 and W-2, and 1997 Plant A-1 data.
(5) Based on a Projected Cycle 13 length of 500 EFPD.
(6) Database applied includes 1996 Plant A-2 and 1997 Plant A-1 data. Tube burst probability is slightly different from that in Reference 8-8 as 1996 Plant W-2 data is not included.
S:\spc\dlw97\ Cycle 13,90d. doc 7-4
8.0 References 8-1 NRC Generic Letter 95-05, " Voltage-Based Repair Criteria for the Repair of Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," USNRC Office of Nuclear Reactor Regulation, August 3, 1995.
8-2 SG-96-07-009, " Beaver Valley Unit-1 1996 Alternate Repair Criteria 90-Day Report," Westinghouse Electric Corporation, July 1996.
8-3 WCAP-14277, Revision 1, "SLB 12ak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections", Westinghouse Nuclear Services Division, December 1996.
8-4 EPRI Report NP 7480-L, Addendum 1, " Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate repair Limits," Electric Power Research Institute, November 1996.
8-5 U.S. N.R.C. Report, " Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No.198 to Facility Operating License DPR-66 Duquesne Light Company, Ohio Edison Company and Pennsylvania Power Company, Beaver Valley Power Station, Unit No.1 Docket No. 50-334", April 1, 1996.
8-6 Letter from B. W. Sheron, Nuclear Regulatory Commission, to A. Marion, Nuclear Energy Research Institute, dated February 9,1996.
8-7 Document Identifier 51-1264500-00, " Probe Wear Monitoring at Beaver Valley Power Station Unit-1 October 1997 UIR12," Framatome Technologies, November 1997.
8-8 Ixtter 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.
8-9 Attachment to Duquesne Light Company letter to U. S. Nuclear Regulatory Commission, " Beaver Valley Power Station, Unit No.1, Docket No. 50-334, License No. DPR-66, Steam Generator Pulled Tube Data (Supplemental) Supponing Alternate Plugging Criteria Implementation," dated March 27,1996.
S:\apc\dtw97\ Cycle 13,90d. doc 8-1
a 8-10 Letter from E. J. Sullivan, Nuclear Regulatory Commission, to D. J. Modeen, Nuclear Energy Research Institute, dated January 20,1998.
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