ML20197B304

South Tx Unit 1,Cycle 8 Voltage-Based Repair Criteria Rept

ML20197B304
Person / Time
Site:	South Texas
Issue date:	12/31/1997
From:	HOUSTON LIGHTING & POWER CO.
To:
Shared Package
ML20197B258	List: ML20197B304 NOC-AE-0044, Forwards voltage-based Repair Criteria 90-day Rept for SG Tube Exam Performed Under NRC GL 95-05 During Seventh Refueling Outage
References
SG-97-12-006, SG-97-12-6, NUDOCS 9712230340
Download: ML20197B304 (53)

Text

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SG-97-12 006 SOUTH TEXAS UNIT - 1 CYCLE 8 VOLTAGE-BASED REPAIR CRITERIA REPORT

e December 1997 9

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Table of Contents Page No.

1.0 Introduction 1-1 2.0 Summary and Conclusions 2-1 3.0 EOC-7 Inepection Results and Voltage Growth Rates 3-1 3.1 EOC-7 Inryection Results 3-1 3.2 Voltage Growth Rates 3-2 3.3 NDE Uncertainties 3-4 3.4 Probability of Prior Cycle Detection (POPCD) 34 3.5 Assessment of RPC Confirmation Rates 36 3.6 Probe Wear criteria 3-7 4.0 Database Applied for Leak and Burst Correlations 4-1 5.0 SLB Analysis Methods 5-1 6.0 Bobbin Voltage Distributions 6-1 6.1 Calculation of Voltage Distributions 6-1 6.2 Probability Of Detection (POD) 62 6.3 Limiting Growth Rate Distribution 6-2 6.4 Cycle Operating Period 6-2 6.5 Projected EOC-8 Voltage Distributions 6-3 6.6 Comparison of Actual and Projected EOC-8 Voltage Distributions 6-3 7.0 SLB Leak Rate and Tube Burst Probability Analyses 7-1 7.1 Leak Rate and Tube Burst Probability for EOC-7 7-1 7.2 Leak Rate and Tube Burst Probability for EOC-8 7-2 8.0 References 8-1 S:\\ ape \\tgx9i \\ EOC790d. doc i

D

South Texas Unit - 1 End of Cycle 7 Voltage Based Repair Criteria Report 1.0 Introduction This report provides a summary of the South Texas Unit-1 steam generator bobbin and rotating pancake coil (RPC) probe inspection at tube support plate (TSP) intersections, together with postulated Steam Line Break (SLB) leak rate and tube burst probability analysis results, in support of continued implementation of the 1.0 volt voltage-based repair criteria for Cycle 8 as atlined in the NRC Generic Letter 95-05 (Reference 8.1).

Information required by the Generic Letter is provided in this report including SLB leak rates and tube burst probabilities calculated using end of cycle (EOC) conditions for the recently completed cycle (Cycle 7) and projection of bobbin voltage distributions, leak rates and burst probabilities for the ongoing cycle (Cycle 8).

Analyses for Cycle 7 were carried out using the actual bobbin voltage distributions measured during the EOC ', outage and the results compared with corresponding values from projections performed based on the last (EOC-6) bobbin voltage data.

The methodology used in these evaluations is in accordance with that utilized for the analyses performed during the last outage (Reference 8.2), which in consistent with the Westinghouse generic 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 8) based on the 1.0 volt repair criteria. These analyses utilized bobbin voltage distributions measured during the recent (EOC-7) inspection and a limiting growth rate distribution from the last two inspections (EOC 6 and EOC-7 inspections).

Two other supplemental evaluations are also presented in this report. One of them c2 amines probability of detection for Cycle 6 inspection (probability of prior cycle detection - POPCD) and the other assesses the fraction of the indications that showed no degradation during RPC inspection in the 1996 EOC-6 inspection, were left in service at beginning of cycle 7 (BOC-7), and were RPC confirmed in 1997 at EOC-7.

Tubes were pulled from South Texas Unit-1 during tue March 1995 inspection, and per the Generic Letter 95-05 requirement no additional tube pulling is required until the outage after January 1998 (34 months after the last tube pull).

Therefore, no tubes were pulled during the September 1997 outage.

S:\\npc\\tgx97\\EOC790d doc 1-1 a

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-i 2.0 Summary and Conclusions -

A total of 1151 indications were found in the EOC-7 inspection of which 15 were inspected with a RPC probe (including all 9 indications detected above 1 volt), and 5 were confirmed as flaws.- SG C had the largest number ofindications among the four SGs with 488 bobbin indications, of which only 5 were above 1.0 volt. All 5 indications above 1 volt plus two other indications below 1 volt were inspected by RPC and 4 were confirmed as flaws. No ID indications at dented TSP intersections or circumferential indications' at the TSP intersections or indications extending outside the TSP were found in this inspection.

SLB leak rate and tube burst probability analyses were performed for the actual EOC-7 bobbin voltage distributions as well as the projected EOC-8 bobbin voltage distributions. EOC-7 actual measured bobbin voltages are all equal to or lower than the corresponding projections performed using the EOC-6 outage bobbin voltage data and a probability of detection of 0.6. The actual number ofindications detected in all SGs during the EOC-7 inspection is 25% to 35% below the corresponding projections. The SLB leak rate and tube burst probability values based on the actual conditions show even larger margins, although the absolute magnitude of these quantities are small.

The leak rate and tube burst probability projections at EOC conditions for the current cycle (Cycle 8) are also well within their acceptable limits. The limiting 4

SLB leak rate projected for the EOC-8 conditions using the NRC SER endorsed probability of detection of 0.6 is 5.3x10 3 gpm. This value is projected for SG-C

~

which has the largest number ofindications, and it is about 3 orders of magnitude below the allowable EOC-8 leakage limit of 5.0 gpm (room temperature). The highest tube burst probability,9.4x10 5, is predicted for SG-A which has the largest indication found in the EOC-7 inspection, and it is also decades below the NRC reporting guideline of 10 2, As the magnitudes of the projected EOC 8 leak rates and tube burst probabilities 2

are very small, there is some potential for the leak and burst results based on the actual EOC-8 conditions to exceed their projections. Occurrence of just a few indications in the modest voltage range of 3 to 4 volts, which is not considered highly improbable, can result in the actuals exceeding their projections. Even if i

the SLB leak rates and tube burst probabilities for the actual EOC-8 conditions exceed their projections by a factor of 5 to 10, they would still be about 2 orders of

. magnitude below their respective limits.

Probability of detection (POPCD) for EOC-6 inspection was assessed using EOC-6 and.EOC-7 inspection data. The results support a detection probability greater than the NRC mandated value of 0.6. Two of the 5 EOC-6 RPC NDF indications S.\\apeugx97\\ EoC790d doc 2-1 a

leR in service during Cycle 7 were RPC tested during EOC-7 inspection and neither was confirmed. There is currently too small a RPC NDF database to recommend a confirmation rate for use in projection analyses. All RPC NDF indications are included in the EOC-8 projections presented in this report.

S \\apc\\tgx97\\EOC790d doc 2-2

- ~.

3.0 EOC-7 Inspection Results and Voltage Growth Rates 3.1 EOC-7 Inspection Results According to the guidance provided by the NRC Generic Letter 95-05, the EOC-7 inspection of the South Texas Unit-1 SGs consisted of a complete,100% eddy current (EC) bobbin probe full length examination of the *ube bundles in all four SGs. A 0.610 inch diameter probe was used for all hot and cold leg TSPs where voltage-based repair criteria was applied. Subsequently, RPC examination was performed for all indications with an amplitude above 1 volt. Nine indications (all hot leg indications) had a bobbin voltage above 1 volt; 3 were confirmed as flaws and were plugged. All cold leg indications had a bobbin voltage below 1 volt.

No unexpected eddy current results were found in this inspection. There were no RPC circumferential indications at the TSPs, no indications extending outside the TSPs, and. no RPC indications with potential ID phase angles. Also,- no mixed residual artifact signals or signal interference from copper deposits were found during this inspection.

A summary of EC indications for all four SGs is shown on Table 3-1, which tabulates the number of field bobbin indications, the number of those indications that were RPC inspected, the number of RPC confirmed indications, and the number ofindications removed from service due to tube repairs. The indications that remain active for Cycle 8 operation is the difference between the observed and the ones removed from service.

Overall, the combined data for all four SGs of South Texas Unit-1 show the following.

Out of a total of 1151 TSP indications identified during the inspection, a total of 15 were RPC inspected.

Of the 15 RPC inspected,5 were RPC confirmed.

A total of 18 indications were removed from service of -which only 3 indications ' vere repaired because of TSP outside diar

.er stress corrosion cracking (ODSCC) related causes (others repaired for non-ODSCC causes).

No cold leg TSP _ ODSCC indications required repair. Consistent with the 1 volt repair criteria, indications with bobbin amplitude less than or equal 1.0 volt were not considered for removal from service, regardless of RPC data.

Only three indications were found in tubes near the wedge supports for s.\\apc\\tg:97\\EOC790d. doc -

3-1

y ll.,

which voltage-based repair criteria does not apply, and they all had a bobbin voltage less than 0.25 volt They were inspected with a RPC probe, and no degradation was detected.

A review of Table 31 indicates that more indications (a quantity of 475 indications, with only 2.above 1.0 volt) y ere returned to service in SG-C than the other SGs, thereby it potentially will be the limiti - SG at EOC-8 from the standpoint of SLB leak rate and tube burst.

Figure 3-1 shows the actual bobbin voltage distribution deterrained f om the EOC-7 EC inspection; Figure 3-2 shows the population distribution of those EOC-7 indications removed from servic, due to tube repairs; Figure 3-3 shows the distribution for indications returned to service for Cycle 8. Of the 18 indications removed from service, only 3 indications are in tubes repaired because of the TSP voltage-based repair criteria.

The rest are in tubes plugged for degradation mechanisms other than ODSCC at TSPs. Three bobbin indications found in tubes near the wedge supports were not RPC confirmed; therefore, they were left in service.

The distribution of EOC-7 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 (992 out of 1152 indications occurred at hot leg intersections in the first three TSP above the flow distribution bafile plate), although the mechanism extended to higher TSPs. Only 15 indications were detected on the cold leg side. This distribution indicates the predominant temperature dependence of ODSCC at South Texas Unit-1, similar to that observed at other plants.. Two single volumetric indications were identified near the flow baffle plate, and they were repaired since the present voltage-based repair criteria do not apply to them.

i A total of 29 dents with a bobbin voltage over 5 volts were found at TSPs in all 4 SGs combined. (Dents called within 0.5" in the topmost TSP and within 0.4"in the remaining TSPs are considered to be within TSP.)

All dented TSP intersections above 5 volts were inspected with a RPC probe in this inspection, and no degradation was found at those locations. Four other dents above 5 volts called between 0.4" to 0.5" were also RPC inspected and found to be NDF.

3.2 Voltage Growth Rntes For projection of leak rates and tube burst probabilities at the end of Cycle 8 operation, voltage growth-rates were developed-from EOC-7 (September 1997) inspection data and a reevaluat on of the EOC-6 (May 1996) inspection EC signals i

S:\\apcugx97\\EOC790d doc 3-2

for the same indications. Table 3 3 shows the cumulative probability distribution for growth rate in each South Texas Unit-1 steam generator during Cycle 7 (July

'96 - September '97) on an EFPY basis, along with the corresponding Cycle 6 growth rate distributions. Cycle 7 growth data are also plotted in Figure 3 5. The curve labelled ' cumulative' in Figure 3-5 represents averaged composite growth data from all four SGs.

Average growth rates for each SG during Cycle 7 are summarized in Table 3-4. It is evidrat that the absolute magnitude of average growth in all SGs is relatively small. Among the four steam generators, SG-A has a slightly larger average voltage growth during Cycle 7. and SG-C has the indication with the largest voltage growth (see Table 3-3). The average growth rates over the entire voltage range vary between 14.1% and 25.0% (of the BOC voltage) per EFPY, between SGs, with an overall average of 19.5% per EFPY. The small average BOC voltages

(< 0.3 volt) leads to the relatively large percentage growth even the average growth

($ 0.072 volt per EFPY) is very small. The average growth for indicatione greater than or equal to 0.75 volt is 1.4% per EFPY and for indications less than 0.75 volt it is 20.7% per EFPY There are only 21 indications with BOC voltage 2 0.75 volt (in comparison to 161 indications below 0.75 volt) of which 10 have a negative growth value. Therefore, there is insufficient data to reliably define growth trend for indications with bOC voltage 2 0.75 volt. Figure 3-6 is a plot of voltage growth during Cycle 7 vs. BOC-7 voltage. It is evident from Figure 3 6 that the Cycle 7 grcwth data for South Texas Unit-1 SGs do not show any dependency on BOC-7 voltage since the tail of the growth distribution (say, abovt BOC voltage 0.6 volt) has no large growth values and contains roughly the same number of positive and negative growth values. Steam generator A had the highest average voltage at BOC-7 as well as the largest average voltage growth during Cycle 7.

Steam generator B had the largest voltage growth rate during the last (EOC-6) inspection, although it is not significantly larger the Cycle 7 growth.

Averaged composite voltage growth data from all four steam generators for the last two operating periods are 5 ummarized in Table 3-5. It is evident that the average growth rate during Cycle 7 is slightly higher than those during Cycle 6. In Figure 3-7, cumulative probability distribution for composite growth rate data from all SGs during Cycle 7 is compared with that for Cycle 6.

Although the average growth rate for Cycle 6 is less than that for Cycle 7, growth values corresponding to cumulative probability over about 0.S (essentially positive growth values) are slightly higher for Cycle 6; therefore Cycle 6 is considered more limiting than Cycle

7. Cycle 6 has a lower average growth rate because it has more negative growth values, but it also has larger positive growth values than Cycle 7. Therefore, Cycle 6 has a more limiting cumulative probability distribution for growth.

The guidelines in Generic Letter 95-05 require the use of more conservative growth Shpeugx97\\EoC790d doc 3-3

rate distributions from the past two inspections for projecting EOC distributions fer the ner operating cycle. From Figure 3-7 it is evident that for positive growth values Cyclu 6 has a slightly larger growth rate than Cycle 7; hence, Cycle 6 growth rates were used to develop EOC-8 predictions. Cycle 6 growth rates for SGs B and D are slightly higher than the composite growth distribution and, per the methodology described in Referenec 8.3, SG-specific growth rates are to be used for SGs B and D while the composite growth rates should be applied for SGs A and C.

Table 3-6 lists the top 30 indications on the basis of Cycle 7 growth rates in descending order.

Four of those indications were.RPC confirmed and the remaining 26 were not inspected. Fourteen of the 30 indications shown are new indications, and EOC-6 voltages used to estimate growth rates for them were obtained by revaluating the last inspection data.

It is noted that in commenting on the last South Texas Unit-190-day report (Reference 8.2), the NRC recommended that the structural and upper repair limits be based on the larger of 307c per EFPY or the SG-specific values. Since Cycle 6 growth rate for SG-B was 337c, its value was conservatively used to estimate structural and upper repair limits for the EOC-7 inspection. However, the peak growth rate for all SGs during Cycle 7 are well below 30% per EFPY; hence, structural and upper repair limits for the EOC-8 inspection should based on 30%

per EFPY growth rate.

3.3 NDE Uncertainties The NDE uncertainties applied for the Cycle 7 voltage distributions in the Monte Carlo analye,es for leak rate and burst probabilities are the same as those previously reported in the South Texas Unit-1 voltage-based repair criteria report of Referer.ce 8.2 and NRC Generic Letter 95-05 (Reference 8.1).

They are presented in Table 3-7 as well as graphically illustrated in Figure 3-8. 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 10.3% about a mean of zero with no cutoff. These NDE uncertainty distributions are included in the Monte Carlo analyses for SLB leak rates and tube burst probabilities based on the EOC-7 actual voltage distributions as well as for the EOC-8 projections.

3.4 Probability of Prior Cycle Detection (POPCD)

The inspection results at EOC-7 permit an evaluation of the probability of detection (POD) at the prior EOC-6 inspection. For voltage-based repair criteria S \\opc\\tgx97\\EoC790d doc 3-4

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-6 inspection can then be defined as follows.

EOC-6 cycle reported

+ Indications confirmed indications confirmed by and repaired in EOC-6 RPC in EOC-6 inspection inspection POPCD =

(EOC-6)

( Numerator)

+

New indications RPC confirmed in EOC-7 inspection POPCD is evaluated at the 1996 EOC-6 voltage values (from 1997 reevaluation for growth rate) since it is an EOC-6 POPCD assessment. The indications detected at EOC-6 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-7. 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-7 indications not reported in the EOC-6 inspection. The new indications include EOC-6 indications present at detectable levels but not reported, indications present at EOC-6 below detectable levels and indications that initiated during Cycle 7.

Thus, this definition, by including newly initiated indications, differs from the traditional POD definition. 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.

The above definition for POPCD would be entirely appropriate if all EOC-7 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 appapriate 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 1997 EOC-7 indications not RPC S:\\apc\\tgx97\\ EoC790d doc 3-5

?.

inspected since inclusion for the EOC-6 inspection could increase POPCD by including indications on a tube plugged for non-ODSCC causes which could be RPC NDP indications. In addition, the objective of using RPC confirmation for POPCD is to distinguish detection ofindication at EOCn.i 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-7 RPC confirmed by RPC confirmed plus not RPC inspected in the above def'mition of POPCD.

For this report, both POPCD definitions are evaluated for South Texas Unit-1.

The POPCD evaluation for the 1996 EOC-6 inspection data is summarized in Table 3-8 and illustrated on Figure 3 9. As seen from Table 3 8, there were only 6 RPC confirmed indications from EOC-6 inspection which is ir.suflicient to define a POPCD distribution for EOC 6 inspections based on RPC confirmed indications only. Therefore, only results based on RPC confirmed plus not RPC inspected indications are shown in Figure 3-9. It is evident that South Texas Unit-1 POPCD values support a POD significantly higher than the NRC mandated value of 0.6. A genenc POPCD distribution developed by analyses of 15 inspections in 8 plants and presented in Table 7-4 of Reference 8-4 is also shown in Figure 3 9. It is seen from Figure 3-9 that the POPCD values for South Texas Unit-1 are equal to or better than the generic POPCD in the voltage range 0.2 to 0.8 volt. There were only a total of 10 indications in the voltage range 0.8 to 1.5 volts in the EOC-6 inspection which is insuflicient to provide a POPCD distribution in that voltage range. With sparse data, a single missed indication can exaggerate the POPCD value; for example, there are only thr 2 indications in the voltage range 1 to 1.5 volts and one missed indicatiens out of 3 has resulted in the POPCD value for the voltage range 1 to 1.5 volts to drop to 0.67 (see Table 3-8). Hence, only POPCD values up to 0.8 volt are shown in Figure 3-9.

In summary, the South Texas Unit-1 EOC 6 POPCD supports a POD higher than the NRC mandated POD value of 0.6.

However, POPCD values could not established reliably above 0.8 volt since the data is sparce..

3.5 Assessment of HPC Confirmation Rates This section tracks the 1996 EOC-6 indications were left in service at BOC-7 relative to RPC inspection results in 1997 at EOC-7. The composite results for all sos are given in Table 3-9.

For 1996 bobbin indications left in service, the indications are tracked relative to 1997 RPC confirmed,1997 RPC NDF,1997 bobbin in ications not RPC inspected, and 1996 bobbin indications with no d

S.\\npc\\tgx97\\EOC790d doe 3-6 i

- ~ - - - - -

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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.

Only 5 EOC-G RPC NDF indications were in service at BOC-7, of which 2 were RPC tested during the EOC-7 inspection and neither were confirmed. Therefore RPC confirmation rate for prior RPC NDF indications is 0%.

It has been recommended by industry that the largest RPC NDF confirmation rates over the prior two cycles be used for projections. There is currently too small a RPC NDF database to recommend a confirmation rate for use in projection analyses. All RPC NDF indications are included in the EOC-8 projections.

3.6 Probe Wear Criteria An alternate probe wear criteria approved by the NRC (Reference 8.6) was applied during the EOC-7 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 since the last successful probe wear check be reinspected with a good probe.

As the repair limit is 1 volt, all tubes containing indications for which worn probe voltage was above 0.75 volt were inspected with a new probe. Only 5 tubes had to be retested based on this probe wear criteria, and the voltages from both worn and -

new probes for all indica +bns in those tubes are shown in the table below.

SG Row Col TSP Worn Probe New Probe Comments Volts Volts A

21 93 2H 0.81 0.32 29 95 2H 0.76 0.37 E

1 14 14C 0.83 0.7G C

41 48 4H 0.77 0.35 2H 0.11 0.11 See note below table D

24 38 2H 0.84 0.79 Only indication below 0.75 volt present in tubes retested for probe wear No new TSP indications were detected in tubes retested for probe wear. Also, from the above table it is evident that restesting did not cause an indication sized below the repair limit to exceed the 1 volt limit after retesting. The maximum ditTerence between voltages based on the worn and probe responses is below 0.5 volt.

s \\ ape \\tgx97\\EOC730d de 3-7

7.

.o Table 3-1 South Texas Unit 1 September 1997 Outage Summary of Inspection and Repair ForTubeS in Service During Cycle 7 Steam Generator A Steam Generator H Composite of AllSGs In-Senice Ibring Cyde 7 RTS for Cycle 8 In-Senke Ihring Cyde 7 RTS for Cyde 8 In-SenLe Ikdng Cyde 7 RU far Chle 8 cdme=4 C dwoud M

apC NK hamm A8 C dwoud M

g 3, g nard

,g Ric i.d a m

^"

gg prc sadraemme AN vause s wid a ws ta=reewd E**==

A Nae 3ngeced

&h n, twaned Repened h asmiet y =a n.r

4 Rer==ed ladic==

g,,p,,,,4 g,,f,,,d Reped WM be.lec atum Oth g.

9,deas

i. dea o.e, hidic====

g,,,,, g g g, $irmaans 6.dx anoa.

0.1 2

0 0

0 2

2 2

0 0

0 2

2 21 I

I I

20 20 01 30 1

0 0

30 29 23 1

0 0

28 27 222 2

0 1

228 219 0.3 52 I

I O

$2 52 48 1

0 0

48 47 317 3

I 2

315 313 04 48 0

0 0

48 48 16 0

0 1

35 35 232 0

0 3

229 229 05 II o

O O

41 11 16 0

0 0

16 16 159 0

0 1

15R 158 06 19 0

0 0

19 19 9

0 0

0 9

9 97 0

0 2

95 45 07 6

0 0

0 6

6 7

0 0

1 6

6 46 0

0 4

42 42 08 6

0 0

0 6

6 8

0 0

0 8

8 28 0

0 1

27 27 09 3

0 0

0 3

3 0

0 0

0 0

0 12 0

0 0

12 12 l'

O O

O I

I O

O O

O O

O 8

0 0

0 8

8 1,I O

O O

O O

O O

O O

O O

O 3

3 2

2 1

0 L2 l'

t 0

0 1

0 0

0 0

0 0

0 I

I O

O I

O l.3 l'

i 0

0 1

0 0

0 0

0 0

0 2

2 0

0 2

0 16 0

0 0

0 0

0 0

0 0

0 0

0 1

I I

1 0

0 1.7 0

0 0

0 0

0 0

0 0

0 0

0 1

I O

O I

O is i'

i 0

0 1

0 0

0 0 -

0

'O

-0 ~

~ l 1

0 0

I O

T<xd 201 5

I 0

201 197 154

_. 2,,

., 0 _,

2 152 ISO

_II51 15 5

18 1833 1823

>Iv 3

3 0

0 3

0 0

0 0

0 0

0 9

0 3

3 6

0 l

Steam Generator C Steam Generator D In-Senice thring Cyde 7 R75 for Cyde 8 In-Senke Ihring Cyde 7 RTS for Cyde 8

- - c _ m""":~_

~,-.

R-AD RPC RPC andamensen AN

'd"

w_m RPC Fff M atmes

=

~

R-0.1 10 I

I I

9 9

7 0

0 0

7 7

0.2 100 0

0 1

99 99 64 0

0 0

64 64 03 136 1

0 2

134 133 81 0

0 0

81 81 0.4 79 0

0 1

78 78 69 0

0

,l 68

_ 68 O_5 63 0

0 0

63 63 49 0

0 1

48 48 06 52 0

0 2

50 50 11 0

0 0

17 17 l

0.7 20 0

0 2

18 18 13 0

0 1

12 12

)

)

08 10 0

0 9

9 4

0 0

0 4

4 09 7

0 0

0 7

7 2'

O O

O 2

2 f

1 6

0 0

0 6

6 l'

O O

O 1

1 1.1 2*

2 2

2 0

0 l'

I O

O I

O l.2 0

0 0

a 0

0 0

0 0

0 0

0 FOOTNOTTc Indications in bins with less than 3 13 l'

I o

0 I

o 0

0 0

0 0

0 indications were considered at their actual I6 l*

I I

8 0

0 0

0 0,

0 0

0 rTrasured voltage (rather assigning a rarnknn valut 13 l'

I O

6 1

0 0

0 0

0 0

0 in the bin range)in the leak rate and tube bunt i8 0

0 0

0 0

0 0

0 0

0

'O O

probability analyses.

Total 488 7

4 13 4 75 472 308 1

0 3

305 304

>lv 5

5 3

3 2

0 1

I o

O I

o 3-8

....m,-.,~

.j Table 3-2 South Texas Unit I September 1997 TSP ODSCC Indication Distributions for Tubes in Service During Cycle 7 Steam Generator A Steam Generator B Composite of All SGs Nmber o(

Maumum A urage Largest Average Nmber uf Mzumem Ascrage tsges Average Nmber of Maumarm Average Imgew Average Tube Supp1:

In6 carum Vohage

.Vottage Goeth Growth inchcwm Vohage Yohage Growd G rath Indscarnes Voltage Vohage Growtis Growth 0 08 0211 56 1.26

_O 45

, 0 55,

O_14 75

, 0 78 _

_ 0 38 0 30...

0 _05 _

__523 _

l />4_, _ 0.f3 035_

_ 0 00 Plate 0 31I,

37 0 98_

0 41 0 42 0.10 21

, 0 73

_ 0.34 024

_0 02

,189 1.54 0 40

_ 0 89 Oill 75 1.75_

033 0 61 0 07 37 0.66,

_0.28.

0 14

, _ 0 0_3 _

_ "'30

_ l.75. _

_ 033 0 61 _

0 06 0511.

17 G30 0 27 0 25 0 06 7

_ 0 39 0 30

_ 0.24 0 06

_060

, 0.24. _

0 25 0 05 79 06H 3

0 25 0.18 0 15 0 06 7

0 41 0 28 0.18 0_06 27

_ _0.51 0.25

_.020,

0 04 0 711 4

0 28 0 17 0 04 0 01 I

') 18 0.18

-0.01

-0 01 20 0.49 0 25 0.24 0 04 0811 2

OJ4 0 12 0 07 0 05 1

0 29 0 29 0 00 0 00 14 0 31 0.19 0.13 0 03 t

0 74 0 74 0 26 0 26 3

0 74 d 4J 0.26

'0 f0 0911 0

1 011 1

0 24 0 24 0 00 Ofu O

I 0 24 0 24 0 00 0 00 llc l

04 0.14 0 02 0 02 1

0 2b 0 26 0 01 0 01 3

0 61 0 34 0 02 0 01 12C 0

1 0.25 0 25 0 02 0 02 2

0 39 0 32 0 04 0 03 13C 0

1 0.10 0 to 0 06 0 06 2

0 10 0 09 0 06 0.02 IfC I

0.16 0.16 0 02 0 02 0

1 0 16 0.16 0.02 0 02 19C 0

1 0.78 0 78

_-0 04

-C M 2

0.75 0.78 Oli 0 09 20C 0

0 1

0 42 0 42

-003

-0 03 2tC 3

0.25 0.18 0 ll 0 03 0

3 0.25

0. l!

0.11 0 03 22C I

0.21 0 21 0 03 0 03 0

1 0 21 0 21 0 03 0 03 1851 Totsi 201 154 Steam Generator C Steam Generator D Nmber of Maumum Average Largest Average Number of Maurrmm Average Larges Average indicatum Vohage Vohage Growet Growth Indicatmns Vohage Voh.ge Growth Growth Tu U211 214 1.64 0 38 0;42 0.08 178 1.02 _

_ 0.37

'1.31 0 06 0.33 0.18 0 03 0 311 94

?.54 0.43 0.89 0.12 37 _

. 0 67 _

_ 0 31_

_ 0.16_ _

_0 04_ _

04_1 134 0 97 0.31 0 55 0 06 34 _ _

0.70_

1 0511 28

.0 60 0 25

_ 0 22 0 05 27 _ _0;42 _

_0 2 t _

_ 0.12 0,0_3_

0611 13 0.51 025 0 20 0 02 4

0 33_

_0. 23_._

0.14 _

0 06 _

0.29_ _

_ 0.24

_ 0 05 _

0711 3

0.23 0.19 0 13,

_ 0.04

_12

_0.49. _

_ _0_.20_

0 13 0 04 _

0811 1

0 !6 0 16 0 04

-004 10

_0 31 0 911 1

0.29 0.29 0 07 0.07

.I 0.28 0 28

-0 02

-0 02 1 011 0

0 IIC 0

1 Ofl 0 61.

__ 0 03 0 01 _

12C 0

1 0.39 _

_ 0.39 0 04

_ _ 0 04.

13C 0

1 0 07 0 07

-0 02

-0 02 16C 0

9 19C 0

1 0.78 0 78 0 21 021 20C 0

7._

0 42_

0 42_

_ -0 03

_ ;0 03_

2tC 0

0 22C 0

0 Total 488 308 w-.m e :n== w rw 3-9 M

.u,

.et Table 3-3 South Texas Unit.1 September 1997 Signal Growth Statistics For Cycle 7 on an 72FPY Basis

. Steam Generator A Steam Generator R -

Steam Generator C :

Steam Generator D Commistive pegg C de 6 C cle 7 C3tle 6 Cycle 7 Cycle 6 Cycle 7 C3cle 6 Cycle 7.

Cycle 6 Cycle 7 3

3 CIVF CPDF CfDF.

CPDF CPDF CPDF'

.CPDF CPDF CPDF CPDF 08 0.0 0

0.0 0.0 '

O 0.0 -

0.0 0

0.0 0.0(M -

0 0.0 0.001 0

Of'

-0.6 0 006 '

O 0.0 00 0

0.0 '

O.0 0

0.0 01XM 0

0.0 0.002 0

0.0

-04 OJxm 0

00 0.0 0

0.0 OJX)5 O.

0.0 0.007 0

0.0 0.005 0

0.0 -

-03 0.041 0

0.0 0.0 OJX)6 0 025 0

0.0 0.011 0

0.0 0.021' I

0.001

.U.2 0.088 0

0.0 OJX)8 0

OJX)6 0.073 3

O (X6 0.021 0

0.0 0.053 3

0.o03-

.O.1 0.165 3

0.015 0.072 3

0.026 0.171 4

0 014

. 0.102 8

0.026 0.139 18 :

0.019-0 0.4 40 0.214 0.24 33 0.24 0395 103_

0.225 033 82 0.291 0359 258

_0.243 0.I.

0 688 98 0.701 0.584 84 0.786 0.82 257 0.752 0.628 172_

_0.851_

0.715

'611' 0.774 0.2 0.876 43 0915 0.8,

26 0.955 0.938 94 ;

__0.945 0.86..

44 0.994 0.889

.207 0.954 03 0.971 11 0.97 0.92 7

1.0 0.984 -

- 2I _

0.988 0.937 2,

1.0

.,0.961 4I 0.99 04 0.988 4.

p.99 0.976 0

0.993 3 _ _.

0.994 0.975

_0 _

_0.985

.,.7 0.996, 0.5 0.994 2

1.0 0.992 0

0.998_

,._ 2 _

.0.998_

.0.986_

_0 _

_0.993, 4_.

0.999 0.6 0.994 0

0.992 0

0.998 0_

,0.998 0.99.}

_0_

0.995 0

0.999 0.7 1.0 0

1.0 0

0.998 0

0.998 1.0 0

0.999 0

0.999.

0.8_

0 0.998 1

1.0 0

0.999 l

1.0.

'0 1

0 0

1.0 0

0 1.0

-0 l

Total 201 154 488 308' 1151 1

1 c-. u* nw m m 3-10

.o 1

Table 3-4 South Texas Unit 1 - September 1997 Outage Average Voltage Growth During Cycle 7 -

l Average Voltage Growth Percent Growth Voltage Numoer of Average Voltage l

Rarg Indecations BOC Entire Cyc e Per EFPY

• Entire Cycle

- Por EFPY

• a Composite of All Steam Generator Data Entree Yultage Range i151 0.28 0 069 0.056 24.2 %

19.6%

~

V r,c <.75 Volts II31 0.27 0.070 0.056 25.6 %

20.7 %

2.75 Volts 2I 0.93 0.017 0.013 1.8%

Ii%

^

Steam Generator A Entire Voltage Range 201 0.29 0.089 0.072 31.0%..,

25.0 %

Y oc<.75 Volts 195 0.27 0.086 0.070

_ 31_.8% _

__.25.7%,~

B 2.75 Volts 6

0.E6 0.103 0.156 22.5 %

18.2 %

Steau. Generator B Entire Voltage Range 154 0.28 0.055 0.045 19.4 %

15.6%.

V soc < '.75 Volts 152 0.28 0.059 0.048 21.3%

17.2 %

2.75 Volts 2

0.83

-0.245

-0.193

-29.5%

-23.9%

Steam Generator C Entire Voltage Range 488 0.28 _ _

0.077 0.062,

_ _27 2% _.

_.21.9% _

V noc <.75 Voits 478 0.27 0.079 0.064 29.4 %

23.8 %

2.75 VoltT 10

~l 0.99

~' T02 E '

~~-0.0i8'

-2.2T 78E ~

~

Steam Genera:or D Entire Voltage Range __

308, 0.28. _

0.049, 0.040. _.

17.4 %

14.1 %

V soc <.75 Volts 306 0.28 0.050 0.041

_I 8.1 % _

.14.7% _

~ 2.75 Volts 3

0.92

-0.033

-0.027

-3.6%

-2.9%

i

1. Hawd on Cycle 7 duraten of 432 t+FD(l.233 E1Pi) e Y

CmWhEILMM 03 N 3-11 L

.=

g 3

.o Table 3-5 South Texas Unit 1 September 19't7 Aserage Voltage Growth for Cycle 7 Composite of All Steam Generator Data -

Bobbin Voltage Number of Average Voltage Average Voltage Growth Average Percentage Growth Range Indications BOC Entire Cycle.

Per EFPY Entire Cycle Per EFPY C cic 7 (1996 - 1997) - 452 EFPD 3

Entire Voltage Range -

I151 0.28 0.069 0.056 24.2 %

19.6 %

V wc <.75 Volts 1131 0.27

- 0.070 0 056 25.6 %

20.7 %

2.75 Volts 21 0.93 0.017 0.013 1.8 %

1.4 %

Cycle 6 (1995 - 1996) - 387 EFPD Entire Voltage Range 1018 0.33 0.045 l

0.042 13.6 %

12.8 %

V ue <.75 Volts 978'.

0.31 0.051 0.048 16.6 %

15.6 %

- 2.75 Volts 40 0.89

-0.104

-0098

-11.6%

-11.0%

l l'

1 1-

< inn m.wmnnu se ru 3-12

p e

Table 3 6 South Texas Unit 1 September 1997 Summary of Largest Voltage Growth Rates for HOC 7 to EOC 7 Steam Generator Bobbin Voltage RPC

_New SG Row Col Elevation C3C BOC Growth Confirmed ?

Indication ?

C 16 0311 1.54 0.65 0.89 Y

N A

30 -

70

_ _ 0411,.. _

l.75 1.14 0.61 Y

N A

28 22 0211-1.26 0.71 0.55 Y

N

_C 41 48 (MH 0.97 0.42 0.55 N

N C

42 71 (Mit 0.93 0.38 0.55 N

N C

30 54 0311 0.84 0.34 0.5 N

Y C

31 58 03H 0.91 0.45 0.46 N

N A

27 23 0211 1.2 0.75 0.45 Y

Y A

32

_88 03H 0.8 0.38 0.42 N

N C

42 36 02H 0.79 0.37 0.42 N

Y A

29 84 0311 0.53 0.13 0.4 N

Y A

33 87 (Mil 0.88 0.49 0.39 N

N A

21 21 0211 0.63 0.26 0.37 N

N 9

C 25 57 03H 0.62 0.25 0.37 N

N C

30 52 03H 0.91 0.54 0.37 N

N A

33 81 0311 0.66 0.3 0.36 N

Y C

14 93 02H 0.65 0.29 0.36 N

N A

30 87 0211 0.72 0.38 0.34 N

Y C

39 48 0211 0.34 0

0.34 N

Y A

32 63 0211 0.58 0.26 0.32 N

N C

35 48 0311 0.32 0

0.32 N

Y A

15 15 (MH 0.69 0.38 0.31 N

N C

15 29 02H 0.77 0.46 0.31 N

N C

24 103 03H 0.76 0.45 0.31 N

Y D

41_

57

_ 02H _

0.86 0.55 0.31 N

Y A

37 90 02H 0.48 --

0.18 0.3 N

Y 11 32 106 02H 0.78 0.48 0.3 N

N I

C 16 35; 03H 04

- 0.11 0.3 N

Y C

44 57 (Mil u.49 0.19 0.3 N

Y C

30 88 02H 01 0.4 0.3 N

Y Gmeth Tath5 TIC 6M7 3 22 PM 3-13

-m

'*L Tchle 3 7

, Probe Wear and Analyst Variability - Tabulated Values Analyst Variability Probe Wear Variability Std Dev = 10.3% Mean = 0.0%

Std. Dev = 7.0% - ' Mean = 0.0%

No Cutoff Cutoff at +/ 15%

r Value -

- Cumul. Prob.

- Value Cumul. Prob.

l

-. U.(XXX)5 _

<: 15.0%

0.0(xxx)

-40.0%

g

+

36.0 %

0.00024

- 14.0%

0.02275-

..~..liMXi95-12.0 %

- -. 0.04324 '

-3570 %-~~

~

9

,g 28.0 %

0.00328

-10.0%

0.07656

~

26.0 %

0.00580 9.0%

0.09927

-2 ?.0%

0.00990 8.0%

0.12655

'_ -2270 1I-

' O.01634

. -._.7.0%

0.15866 7

18.0 %

0.04027 5.0%

0.23753^

- 16.0%~ ~

i).060i5 ~

f

-4.0%

0.28385

~ 7T,jjg ~

0.08f04

-3.0%

0.33iif ~

~

_" l ii!U % '

~ 0.12200 2.0%

0.38755 g -

g

_... g g --

~ ~ 5 8,6 %

0.21867 ~

~

1.0%

0.55680 0.0%

0.50000 IU V 028ilil

~

dd%

0.34888

- 2.0%.

0.61245

-2.0%

0.42302 3.0%

0.6658S 0.0%

0.50000 4.0%

0.71615 2.0%.

0.57698 5.0%

0.76247 4.0%-

0.65112. ~ - -

- 6.0 %

0.80432

~ ~E0 V 0.71989 7.0%-

0.84134 8.0%

0.7813F ~

8.0% ~ ~ ~U~8isi~ ~

^ ~iii.0%

U.8N19' 9.0%

0.90073

~

12.0 %

0.87800

' 10.0%

- 0.92344 14.0 %

0.91296 11.0%-

0.94196 16.0 %

84 12.0 %

0.95676

.q

. 0.939_g_.

- g 20.0 %^

~~

~

_-0.973i2__

_ ___ l 4.0%_-

0.97725

~^ 10%

0.99010 _.-

> l5.0%

i.00000 2

- 28.0% -

'u.99672-30.0 %

0.99821

_ 32.0%'

O.99905 _ -

34.0 %

0.99952

_3.T._0%_ ;

0:96_97s_7'..

~

- 38.0%

0.99989

~~ Tiis' O.99995

~

40 l signee Table s.7 ::/is/97 7,to l'M 3 14

Table 3-8 South Texas Unit 1 1997 EOC-7 Evaluation for Probability of Prior Cycle Detection Composite of All Steam Generator Data New Indications In POPCD'..

ln Bobbin 1997 1997 Inspection inspection RPC 1997 RPC 1997

'RPC 1996 RPC Confirmed Voltage

-Inspection

' Confirmed Inspection Co-firmed Inspection Confirmed Plus Not

Bin -

RPC plus not RPC plus not Confirmed Inspected Confirmed inspected Confirmed Inspected and Plugged Frac.

Count

. Frac Count

> 0 - 0.2 1

272 1

157 0

0.5

.1/2.

0.366' 157/429 0.2 - 0.4 0

172 0

351 0

0/0 0.671 351 /523

-0/0 0.805 128/159 0.4 - 0.6 0

31 0

128 0

0.6 -0.8 0

5 1

17 0

1.000 1/1 0.773 17/22

- 0.8 - 1.0 0

2 0

5 0

0/0 0.714 5/7 1 s - 1.5 -

1 1

1 1

1 0.667 2/3 0.667 2/3' TOTAL 2

483 3

659 1

> 1V 1

1 1

1 1

Poped Tablet 11/2667 3 24 PM 3-15

TaDie 3-9 South Texas Unit 1 Analysis of RPC Data from 1996 and 1997 inspections Combined Data from All Steam Generatora l

Total -

Total Total Percent Total l

1996 1997 1997 1997 Group of Indications inspection inspection Inspection inspection Bobbin Bobbin RPC RPC I sWM Indication Indication Confirmed Confirmed Less than or Equal to 1.0 Volt in 1997 Inspection 1996 Inspection Bobbin Left in Servce 1004 657 1

1 100.0

- 1996 Inspection RPC Confinned 0

0 0

0

- 1996 Inspection RPC NDD 3

3 0

0

- 1996 Inspection RPC Not inspected (iS4_

654 1

1 100.0 No 1997 Inspection Bobbin

• 347 I

NM 1997 Inspection Indication

_ 485 5,_

_1_ _

20:0 Surn of All 1997 Inspection Indication 1004 1142 6

2 33 3 Greater than 1.0 Volt in 1997 Inspection 6_ _

6 2_

333 1996 Inspects Bobbin Left in Service 6

g,

_0 _

0

_.._ 0 _

- 1996 Inspection RPC Confirmed 0

- 1996 Inspection RPC NDD 2

_2

_2. _ _ _

_ 0 _..

0.0

- 1996 Inspection RPC Not inspected 4

4 4

2 50.0' No 1997 Inspection Bobbin

• _0 New 1997 Inspection Indication 3

1_

33 3 3

Sum of All 1997 Inspection Indication 6

9 9

3 33.3 All Voltages in 1997 Inspection 1010 663 7

3 42.9 1996 Inspection Bobbin Left in Service 0

0

_0 _

0

- 1996 Inspect,on RPC Confirmed

- 1996 Inspection RPC NDD 5

._ 5 _ _

2 _.

,O.

0.0

- No 1997 Inspection Bobbin

• 347 658 _

5 3

60.0

- 1996 Inspection RPC Not inspected 658 New 1997 Inspection Indication 488 8_

_2

_25.0 Sum of All 1997 Inspectm Indicate 1010 1151 15 5

33.3

• trocatons split es based on 1996 Inspedon tcbtwn vokage 3-16 i

~

i Figure 3-1 l

South Texas Unit 1 September 1997 Outage Bobbin Voltage Distributions at EOC-7 for Tubes in Service During Cycle 7 IM) l l4()

r j 7g.

E3 SG-A

,$ 100 -

n E SG-B go _

g C

tS gj g,

OSG-C 40 -

ESG-D 29 9

/.

k i3 ' "

U 0

=

=

=

s

=

Bobbin Voltage Wiigil 3-17

~

o 1.

Figure 3-2 South Texas Unit 1 September 1997 Outage Bohhin Voltage Distribution for Tubes Plugged After Cycle 7 Service 5

OSG-A 4_

. - ~

~

E SG-B O SG-C Eo 3-8 ESG-D E

D

.c E

2-l

=

4 8

1-ll -l-lll 0

l l

l l

l l

l

[

en m

n in e

n

=

e j

6 6

6 6

6 6

6 6

l Bobbin Voltage themrn hg2 3-18

Figure 3-3 South Texas Unit 1 September 1997 Outage Bobbin Voltage Distributions for Tubes Returned to Service for Cycle 8 160 G SG-A g 4o _

ESG-B j 120 -

i

.2 3 goo _

OSG-C

~

T i.

.E Ej! go _

E SG-D

~

60 -

40 -

20 -

j IE m 1. _ I'l..

b 2

h 2

3. h h.$

h.E M.

g 0.!

0. ',

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

f.!

I.2 is I.7 I.8 Bobbin Valtage 5% e,5 =

3-19

~

o o Dc Figure 3-4 South Texas Unit 1 - September 1997 ODSCC Asial Distributions for Tubes in Service During Cycle 7 250 E SG-A 200 E SG-B l

$150 OSG-C

=

C C

t jig)

EISG-D

]

i 50 l ti c

k (s

A r2

._ N a

9 0211 03:1 0411 0511 0 611 0 711 0511 0911 1011 1IC 12C 13C 16C 19C 20C 21C 22C Tube Suppor: Plate

<- r.,i i-. m 3-20

m

- e.

Figure 3-5

!"outh Texas Unit I Cycle 7 ( July 1996 to &v;s_ix 1997 )

Cumulative Probability Distributions for Voltage Growit on an EFPY Rasis 1.0

, - - -.f4 - -- !

m'_

g,. -

/

0.9 -

1 s<.

g_g.

W~

[

~

=

--+- SG-A x -

m

- ~

--%.a

..w.r

-..e

'5.

fr

- c-SG-B It j

c 0.6 -

g j

fc

-- u -- SG-C -

l' 5 0.5 -

-g 2

11-f f4~

- e-- SG-D i

it i

.I. G.4 -

t.

W-I.I

--x-Cumulative 3

f 5., 03 -

P-(,2

/

-/

0.2 -

/ /-'

QI-

./ /

1

~~

0.0 E -- - - -O -

T 9

q

=

N m

t n

=

=

=

=

=

=

=

=

=

=

=

{

Voltage Grow th I

O he ng2 inw72n tu 3-21

_ = _ _

s.

Figure 34 l

i South Texas Unit -1 September 1997 Outage i

Voltage Growth During Cycle 7 vs BOC-7 Voltage 1.5 J

i i

i i

i t

1 i

j 4

j i,

j i

i o SG-A i

i t

i g

____._i x SG-B o

i i

3 i

a SG-C

~

l i

U i

+

i i

et j

l I

j l

+ SG-D

.5 o

i s

---

j i

=

0;c J

o l

1 i

.c 05 o

l L

I - --- ----

' a o

i i

l i

• o 2

i m m U

b xo a

o o" I

• x

+

i I

I o

i o

o 8

l

-0.5

' x i

l 0

0.2 0.4 0.6 0.8 I

I.2 1.4 1.6 1.8 i

BOC-7 Voltage

{

l GreethGrtiresNelI/26N7 3 23 l'M j

i 3-22 l

i t

• O

) Qi v,m.

Figure 3-7 South Texas Unit 1 -Septesaber 1997 Bobbin Signal Growth His:ory - Cun:ulative Probability Distributions on an EFPY Basis Cosnposite of AllSteam Generators I0 f

• .. c--

w-

.O'..-

i i

/

\\

0.9 -

~

08-O'

~

,07-2 tc 3w 0.6 -

e

.1

-+--Cycle 6 j

I05-i l

1 5

l i

-- C-- Cycle 7

~30.4-s E=

a

) :

03 -

O

/

02-e I

~

t' 01-(

)

o.0 c

~

g

-4 O

=

d y

y y

y y

d D

d D-.

~

d

.D 6

O Voltage Growth mnas nnun s 1s no 3_<j3

s.

i Figure 3-8 NDE Uncertainty Distributions

-...;;;;;;:000^^^

1 s

l 0.9 I

o.g 0.7

.b i

= 0.6 t

.c e:

-e-Analyst Variability 1

i-I 0.5 Probe Wear 1

i

-=

I E

i L

l

@ 0.4 j

4 m

U h

\\

03

+

i i

i i

i i

I 1 --

0.2

+

i I

0.1 i

O 0c00000000000^

-40%

-30%

-20%

-107c 0%

10 %

20 %

307-40%

Percent Variation in Signal Voltage (%)

3-24 ro.c w ir.3.c6 iis m m ru

IillilIl 1l 5

3 l.

}

d e

t c

e 3

l p

sn N

i o

t N

su lP d

e 5

l m

2 r

ifn o

C 6

C-CP O

R E

~

ta 2 e l

D

~

d C

~

u t

1 P iO i

t lp nP m

9Ur A

-3 s o e af n

r x n b

i u e o gTi 5 B bo 5

t i

a 2

Fh t

u

~

l ul 1

a 3

o v S E C-7 O

~-

E

/

79 9

1 l

I s-3 7

/

/-

/ !

j-5 l

0 i-i ! 'f 1

/-/

M P

/

4

/

2

/

3 7f N

0 62/

0 9

8 7

6 5

4 3

2 1

0 I

l 1

0 O

0 0

0 0

0 0

0 0

ilg iF d

cc. 53

• 5

~cs.%

p tP l\\l

'-l'

!l ll!llll 11l!ll

[

E 4.0 Database Applied for Leak and Hurst Correlations The database used for the leak and burst correlations that are applied in the analyses of this report is the same as the voltage-based repair criteria database described in Reference 8.2.

Model Boiler 3,pecimen 598-1 is excluded from the veltage-based repair criteria database based on application of EPRI data exclusion criterion for very high voltage indications and concurrence by the NRC. South Texas 1 and Braidwood.1 pulled tube indications R16C42, TSP 5 (0.28 volt) and y

R2007. TSP 7 (0.38 volt), respectively, are excluded from the correlation based on EPRI data exclusion criterion 2a accepted by the NRC. Criterion 2a excludes indications with burst pressures high on the soltage correlation if the maximum crack depth is less than 607c and there are less than 2 remaining uncorroded ligaments. Plant S pulled tube indication R28C41 is included in the leak rate con elation at a SLB leak rate of 24971ph consistent with NRC recommendations.

South Texas ptdled tube data from 1993 and 1995 inspections are included in the voltage based repair criteria database. This database is in compliance with NRC guidelines for application of leak rate vs. voltage correlations and for removal of data outliers in the 3/4 inch tubing burst and leak rate correlations. This vcltage-based repair criteria database for 3/4" tubes is also documented in Reference 8.5 and it was used to perform the SLB leak rate and tube burst probability analyces

}

reported here.

The database meets the NRC requirement that the p value obtained frma the regression analysis of leak rate be less than or equal to 5.

Therefore, a SLB leak rate versus voltage correlation is applied Ibr the leak rate analyses of this report.

The following are the correlations for burst pressure, probability of leakage and leak rate used in this report.

Burst Pressure (ksD 7.4234 - 2.9920 x log (Volts)

=

I Probability of Leak

=

( 5.1721 - 8.6705 x log (volts) )

y,

Leak Rate (I/hr) 10

=

It is noted that the above burst pressure correlation differs from that shown in Reference 8 2 although both are based on the same database, and the reason being that the above correlation is based on data normalized with flow stress of 71.565 kai whereas the correlation in Reference 8 2 is based data normalized with 75 ksi.

Ilowever, the Monte Carlo burst probability results presented here as well as those SAapeugx97\\EoC790d doe 4-1 L

L

..+

l in Reference 8 2 are based on the same flow stress distribution for' Alloy MA 600 -

(mean = 71,567 kai, standard deviation n 3.5668 kai from a sample size of 627).

}

i

-t

+

t q.

e i

i J

h I

9 d

f F

l 1

n-d

) SimpeNgu97\\EOC790d. doc ~

.4-2

)

R.7 r

9 s.

v

,,a...~-,..

5.0 SLB Analysin hiethods hionte Carlo analyses are used to calculate the SLB leak rates and tube burst probabilities for both actual EOC 7 and projected EOC 8 voltage distributions. The Afonte Carlo analyses account for parameter uncertainty.

The analysis methodology is described in the Westinghouse generic methods report of Reference 8-3, and it is consistent with the methodology applied to leak and burst analyses performed during the EOC-6 outage.

1 In general, the methodology involves application of correlations for burst pres ure, probability ofleak and leak rate to a measured or calculated EOC distribution to cotimate the likelihood of tube burst and primary to-secondary leakage during a postulated SLB event. NDE uncertainties and uncertainties associated with burst pressure, leak rate probability and leak rate correlations are explicitly included by considering many thousands of voltage distributions through a blunte Carlo sampling process. The voltage distributions used in the projection analyses 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 aller a cycle of operation have shown that the Afonte Carlo analysis techniquo yields conservative estimates for EOC voltage distributions and 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.

S iape\\tgu97\\ EoC790d doc 51

\\o o

6.0 Bobbin Voltage Distributions This section describes the salient input data used to calculate EOC bobbin voltage distributions and presents results of calculations to project EOC-8 voltage distributions. Also, EOC 7 voltage projections performed during the last outage based on EOC 6 inspection bobbin voltage data are compared with the actual bobbin distributions from the current inspection.

6.1 Calculation of Voltage Distributions The analysia for EOC voltage distribution starts with a cycle initial voltage distribution which is projected to the end of cycle conditions based on the growth rate and the anticipated cycle operating period.

The number of indications assumed in the analysis to project EOC voltage distributions, and to perform tube Irak rate and burst probability analyses, is obtained by adjusting the number of reported indications to account for detection uncertainty and birth of new indications over the projection period. This is accomplished by using a POD factor, which is defined as the ratio of the actual number ofindications detected to total number ofindications present. A conservative value is assigned to POD based on historic data, and the value used herein is discussed in Section 3-2. The calculation of projected bobbin voltage frequency distribution is based on a net total number of indications returned to service, defined as follows.

Nroi nrs = Ni/ POD Nngina + Ndepioggea

where, Nrot ars =

Number of bobbin indications being returned to service for the next cycle, Ni Number of bobbin indications (in tubes in service)

=

identified after the previous cycle, POD Probability of detection,

=

l Nwsm.a Number of Ni which are repaired (plugged) after the last

=

l

cycle, Na,saggi.a Number ofindications in tubes deplugged after the last

=

cycle and returned to service in accordance with voltage-based repair criteria, i

There are no deplugged tubes returned to service at BOC-7; therefore, Na,pioggea = 0.

The methodology used in the projection of bobbin voltage frequency predictions is S \\ ape \\tgs97\\ LOC 790a doc 6-1

described in Reference 8 3, and it is same as that used in performing EOC 7 predictions during the last (EOC 6) outarm (Reference 8.2). Salient input data used for projecting EOC-7 bobbin voltage frequency are further discussed below.

6.2 Probability of Detection (POD)

The Generic Letter 95 05 (Reference 81) 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 where all indications are detected. A voltage-dependent POD may provide 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 dependent 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 lower 95% confidence bound, and their distribution is graphically illustrated in Figure 61.

6.3 Limiting Grosyth Rate Distribution As discussed in Section 3.2, the NRC guidelines in Generic Letter 95-05 stipulate that the more conservative growth rate distributions from the past two inspections should be utilized for projecting EOC distributions for the next cycle. It is evident from' Figure 3-7 that growth rates for Cycle 6 on an EFPY basis are higher than those of Cycles 7 above a cumulative probability of 0.6; therefore, Cycle 6 growth rate distribution is used to develop EOC-8 predictions. Cycle 6 growth rates for SGs B and D are slightly higher than the all SG composite growth distribution and, per the methodology described in Reference 8.3, SG-specific growth rates are to be used for SGs B and D while the composite growth rates should be upplied for SGs A and C.

6.4 Cycle Operating Period The operating periods used in the growth rate /EFPY calculations and voltage projections are as follows.

Cycle 7

- BOC-7 to EOC 7' - 452 EFPD or 1.24 EFPY (actual)

Cycle 8

-- - BOC-8 to EOC-8 509 EFPD or 1.39 EFPY(estimeted) s3apeugx97\\EoC790d doc 62

=

-gne

-i----e rg.-

+,

e 1

6.5 Projoe:ted EOC 8 Voltage Distribution Calculations for EOC 8 bobbin voltage projections were performed for all four SGs based on the EOC 7 distributions shown in Table 6 2. The BOC distributions were adjusted to acccunt for probability of detection as described above, and the adjusted number ofindications at BOC-8 are also shown in Table 6 2. Calculations wcre performed uaing a constant POD of 0.6 as well as the EPRI POPCD distribution (presen'.ed in Table 61). The larger growth rates for the last two cycles of operation, which are the EOC-6 growth rates shown in Table 6-3, were applied. The EOC 8 voltage distributions thus projected for all four SGs are summarized on Table 6-3. These results are also shown graphically on Figures 6 2 to 6 5. In general, resu!ts based on a constant POD of 0.6 are more conservative than those using the voltage-del.ndent EPRI POPCD.

6.6 Comparison d Actual and Projected EOC 7 Voltage Distributions Table 6-4, and Figures 6-6 and 6-7 provide a comparison of the EOC-7 actual measured bobbin voltage distributions with the corre.ponding projections performed using the last (EOC-6) inspection bobbin voltage data.

EOC7 projections are based on a constant POD of 0.6. As reported in Reference 8-2, SG-C was projected to be the limiting SO and it was confirmed to have the largest number of indications and the largest indication measure.1 in the EOC-7 inspection. The actual peak voltagea measured for all SGs are equal to or le -

.n their projected value.

A comparison of the actual and projected voltage dist :butions in Figures 6-6 and 6-7 show that in general the indication population above 0.6 volts is substantially overestimated in the projections based on a constant POD of 0.6. This POD value is conservative for voltages above about 0.5 volt but non-conservative below 0.5 volt as seen in Figure 61.

S.\\apc\\tgz97 \\ EOC790d doc 6-3 l

l

~._

?.

Table 61 EPRI POPCD C:stribution Based on Post 1992 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..I 0.62

_. _ 0.6 _.

0.67

. _.._0]_

0.73-

_0,8. _

0.77 0.9 0.81

- -.. 1..

0.83

.. = - -

,1.6 0.92 1.8 0.93 2

0.94 0.98

1. Data taken from Reference 8-4 mena s.1 unw m m 6-4 g-f.~-

a,-

g.

w._.

g

.. _ _ _ _ _. _ _ _. -. _ _. ~.. _

Tchle 6 2 r

South Texas Unit 1 September 1997 EOC.7 Field Bobbin ami Assumed HOC 8 Bobbin Distributhms in SLH I,cak Hate and Tube Hurst Anahses Steam Generator A Steam Generator B Vokage IDC.7 BOC.8 EOC.7 BOC.8

[

T M)M'D e

NDPCD Indw m 1 4.c w

_ 0 l___

2 0

3.33 8.33

_2 0

,,_ 3. 3 3_._

8.33 _

~9 2 - _30_

_ 0_.. _

50 00 88 24 28 0

46.67 82.35 0.3

._.J2_. _,.__.O___ _.86_67_ _118 18_ _ 48 0

_ 6100_ j09.09_

04 48 0.

80 00 90.57 36 1

59.00 66.92 05 31 0

$1.67 50 00 16 0

26.67 25.81

- 06

, __ 19,__ _

0 31.67 28.36 9

0 15.00_

13.43 0.7 6

0 10.00 8.22 7

I IJ67 8.59 08 6

0 10 00 7.79 8

0 13.33 10.39 09 3

0 5.00 3.70 0

0 0

0

_l 1

0 1.67 1.20 0

0 0

0

..l..l__ _ _0_,_

_ _0. _

_.0 00_. 0.00 __

0 0

_,_,0__ _ _ 0___

._ j.2 __

l 0

1.67 1.14 0

0 0

0 33

_3._.._.

0

, 1.67 1.12 0

0 0

0 l.4

_. 0 0

0 0

0 0

0 1.5 0

0 0

0 0

0 0

0 16 0

0 0

0 0

0 0

0 1.7 0

,0

, _0 _

_0

_0 0

0

_0_

l8 1

0 1.67 1.OR 0

0 0

0

, Total 201 0

335 00 407.92 154-2 254.67 324 9?

>IV 1

o 5 00 3 31 0

0 0

0 Steam Generator C Steam Generator D Vohese EOC.7 BOC.8 EOC.7 BOC.8 ndes.66 Ind w roo seer.o.ms rop lader mans kepasud 84 Repeared 64 g

0.1 10 1

15.67 40 67 7

0 11.67 29.17 0.2 100 1

16567 293.11 65 0

108.33 191.18 0.3 136 2

224 67 307.09 81 0

135.00 184 09 0.4 79

.I.

130 67 148.06 69 I

. _i_14_00,.. _ l29.19_

0.5 63 0

105.00 101.61 49 1

80.67 78.03 06 52 2

84 67 75.61 17 0

28.33 25 37

_._0;7_ _ 20.

2 31.33 25.40 13 1

20 67 16.81

__08_

l_0__

. _ _ _ _,1 15.67 l 1.99 4

0 6.67 5 19 09 7

0 11.67 8M 2

0 3.33 2.47 I

6 0

10.00 7.23 1

0 1.67 1.20 1.1 2

2 1.33 0.34 1

0

_ _67 _ _ lJ7 _

l l.2 0

0 0 00 0.00 0

0 0

0

_l.3. _ __l_

_,0 1 67,_.._._1.12_

._.0 0

0_ _ _0_

1.4 0

0 0

0 0

0 0

0

_ l.5 _.

O_

0_

10 0

0 0

0 0

1,6 1

_._I l

0 0

0 0

-0

_ l:7_ _, I _.. _

.O, 1.67 1.08 0

0 0

0

- 1.8 0

0 0

0 0

0 0

0

_ Total __

48R 13 A00 3?

1022 04 309 3

512 00 663.87

>lV 5

3 5 33 2 62 1

0 1 67 1.17 4

6-5

-n....

1 7

itWe&3 i

South Texas Unit 1 September 1997 Voltage Distribution Projection for EOC 8 Steam Generator A Stoem Generator B Stoem Generator C Stoem Generator D POD EPRI POD EPMI POD EPRI POD EPRI 0.8 POD 0.8 POD 0.8 POD 0.8 POD VoNege Projected NumberofIndicotions et EOC 0 0.1 2.01 4.37 1.30 2.86 8.24 18.99 5.39 12.21 0.2

_19.14.

33.13 12.16 21.27 62.31 110.12 37.19 65.54 0.4-55.08 73.25 39.01 54.51 129.42 180.99 80.98 112.19 0.5 57.95 71.20 41.90 55.39 123.96 165.45 87.80 114.66 0.6 50.42 57.61 36.05 47.41 111.88 130.83 76.16 91.79 0.7 37.75 40.37 30.52 35.60 84.56 91.04 57.18 64.18 0.8

.25.82 26.14 22.99 25.28 58.77 50.52 39 28 42.06 0.9 16.76 16.16 16.39 16.99 38.96 37.34 25.02 25.71 1.0 10.34 9.48 10.43 10.06 24.64 22.23 15.41 15.25 1.1 6.20 57/

~5.d4 ~

~

5.52 15.21 13.17 9.41 9.23 1.2

?.87 3.39 3.59 3.38 9.50 8.25 6.01 6.04 1.3 2.55 2,16 2.18 2.06 5.72 4.81 3.71 3.60 1.4 1.70 1.36 1.05 0.82 3.25 2.56 2.13 1.96 1.5 1.13 0.86 0.0 0.0 1.98 1.50 1.12 0.77 1.6 0.81 0.64 0.70 0.70 1.40 1.13 0.00 0.00 1.7 0.63 0.49 0.30 0.30 1.03 0.79 0.70 0.70 1.8-0.51 0.34 0.0 0.0 0.73 0.44 0.30 0.30 1.9 0.41 0.0 0.0 0.0 0.51 0.00 0.0 0.0 2.0 0.01 0.70 0.0 0.0 0.0 0.70 0.0 0.0 2.3 0.30 0.0 0.0 0.0 0.30 0.0 0.0 0.0 TOTAL 335.0 1 407.9 254.7 324.9 800.3 1022.1 512.0 664.0

>1V 18.8 15.7 13.9 12.8 40.3 33.7 23.4 22.6 1

I 66

,~_

O Table 6 4 Soutl. Texas Unit.1 September 1997 Coint ar-ison of I'redicted and Actual EOC 7 Voltage Ulstributions Steam Generator A Steam Generator B Stemn Generator C Steam Generator D E#I EOC7 EOC 7 LOC 7 gy

[0C.7 (OC 7 Yonage Prodwuon Predict 6en Pred6ct60n Prod 6ct60n Bin actLal Actual Actual Actual POD e 0 0 PODe0$

POD e 0.6 POD e 0.6 Nurnber of Indicatione 0.1 0.6 2

0.0 2

0.0 10 0.6 7

0.2 6.8 30 3.5 28 22.4 100 7.0 65 0.3 19.5 5._2 16.2 48 75.8 136 33.2 81 0.4 34.0 48 28.2 36 111.2 79 67.3 69 0.5 44.2 31 33.0 18 126.5 63 81.8 49 0.0 45.0 19 33.0 9

112.0 52 79.9 17 0.7 40.8 6

27.9 7

89.4 20 66.5 13 0.8 31.7 6

21.8 8'

67.1 10 49.5 4

0.9 22.9 3

15.4 46.7 7

33.8 2

1.0 15.3 1

10.1 31.0 6

20.5 1

1.1 9.8 0

6.4 19.6 2

11.7 1'

1.2 6.0 1

3.9 12.0 0

6.6 1.3 3.5 1

2.3 7.1 1

3.7 1.4 2.0 0

1.3 4.0 0

2.1 1.5 1.1 0

0.8 2.5 0

1.5 1.6 0.4 0

0.5 1.8 1

1.4

~

1.7 0.7 0

0.7 1.3 1'

1.2 1.8 0.3 1'

O.3 0.9 1.0 1.9 0

0.5 0.9 2.0 0__

0.7 07 2.1 0

0.0 0.0 2.2 0

0.3 0.3

~%

Total 284.6 201 205.3 154 732.8 488 471.8 309

' Bin with the largest indicahon found in the stearn generator 4

67

.m..,,,,,...-

1' I

i L

5 3

3 s

tira 5

fP 2

8]n1 -

m i

sn u odn itc e ed l

pd sA 6

2 e

n 0

d i0 58

=

u t

i 1 4 D

l 7

p n-O m

1 oP P

A

-6 d N d

e n

eet i

t r s a

b r

g ua o d

b p

n o

gB e a

5 B i

F nR M

1 oI C

iR R

tuP N

b E l

irt n si iD de Dtn Ce 1

Ps Ore PP c[

ireneG 5

0

/

M fo S

it 0

TTW 0

9 8

7 6

"5 4

3 2

1 0

s 2

/

t 1

0 0

0 0

0 0

0 0

0 0

st

&rrg

$,~yE e* s.5E.2.

s mm e

e yar i

Figuro 6 2 South Texas Unit 1 September 1997 Projected Bobbin Voltage Distributions for Steam Generator A at EOC 8 POD =0.6 90 80 -

70 -

DBOC b oo.

g,o.

W Prodicted EOC-8 3 4o.

so

.c 20 to rk.

.'E.ra.

.rE ca.

_.m.

o

aaaa

5 0 :

S :

0 5

S aa2 2

Bobbin Voltage EPHIPOPCD 120-100-80 -

O BOC-8 60 -

W Predicted EOC 8 40 -

go

,nB Ll1,..

E E

E E

3 5

U S

I O

E O

O U

N Bobbin Voltage peacomp Fig 6211rt&97 4 06 PM G-9

f h.'

(*

Figure 6 - 3 South Texas Unit 1 Sept,tnber 1997 Projected Bobbin Voltage Distributions for Steam Generator B at EOC-8 POD =0.6 i

to l

so i

I 70 '

O B O C-8 m.

E Predicted EOC-8 I

so l

' 30 l

)

p0 to 0

Ik' B

I o1 02 03 04 06 06 07 08 09 to 1.1 12 13 14 15 16 1.7 Bobbin Voltage p

EPRIPOPCD l

120 100 no.

O BOC-8

}

I N Predicted EOC-8 l

,.o ll m==-==-

.e

==

m, we

, n._

1 i

01 02 03 04 06 06 07 08 09 10 1.1 1.2 1.3 14 16 16 1.7

]

l Bobbin Voltage I

4 J

6-10

1. mmu, a m l

.~

_,,,..,._,,_m.._.,,.,...

,,.-.,m.

l' I

Figuro 6 4 i

South Texas Unit.1 September 1997 Projected Bobbin Voltage Distributions for 9 team Generator C at EOC 8

{

POD =0.6 250 j

l 200-0BOC4

~

WPredicted EOC4 i

)

tm.

a ev.

0

- a "I

~1^""~^~-~

a:

aaa j

Bobbin VoNege r

-w --

EPRI POPCD

~

av :

l 3

OBOC4 y

1 W Predicted E004 iso.

tgo.

i I

60 <

.rI;E.m.

E.

.rE.r 6.

01 02 03 04 0$ 06 0.7 08 0.9 to 1.1 1.2 1.3 14 1.5 96 17 1.8 19 20 2.1 22 Bobbin VoMage 5

F

-. re t w.oi ru 6-11

>e Figuro 6 5 South Texas Unit-1 September 1997 l

Projected Bobbin Voltage Distributions for Steam Generator D at EOC4 POD =0.6 140 DBOC4 goo.

80 -

EPredicted EOC4 I

co.

i j 4o l

20 -

a E-O

^

^ "^ "~ -~

j 0.1 0.2 0.3 04 0.5 06 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Bobbin Voltage EPRI POPCD 200

~

100 <

too -

~

080C4 spo.

- g oo.

I l

E Predicted EOC4 80

, m.

40 go.

E.

,_E I

E.

. r-m.

o O.1 0.2 0.3 04 0.5 06 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Bobbin Voltage

l*

i.

l*g Figure 6-0 South Texas Unit.1 i

l Comparison of I'redicted and Actual Ilobbin Voltage Distributions for Cycle 7 4

I Steam Generator A 60 l

l

~

{

50 -

l l

j,.

^ * ' " * '

l

'E

~

5 Prediction, POD.O.6 x-

, ro.

1

,o

_l 1

.8_.

1

~

05 00 of os 09

,.0 11

,1

.3 14

,6

,7 0,

02 03 04 Ik,bbin Voltage Steam Generator il 40 D Actual i

,f "

N Prediction, POD =0.6

~ ~ '

- ~ - - "

l

} to.

i

!z

,o

._l l l

i L_

I l...__.;

n j

0, c.

,7 soboin voitage i

6 13

......m.-~

~

a FigureG 7 South Texas Unit 1 Comparison of Predicted and Actualllobbin Voltage Distributions for Cycle 7 Steam Generator C l

l too

,,3 D Actual

.i

~~

~ ~ ~

~ ~ ~

E l'redictlon, l'OD.O.6 no.

I so z

so go 0-

"2"2 - ^ - - --

"*"V""*8' Steam Generator D 00 80

---~-

yo

~ --- __ - -. _.

l so i

E l'rediction. I'OD.O.6 g

so.

8w 20 -

J _ _. _ _g l,1 r,

,I I_m... _._ _._ _

e:

liebbin Voltage 6 14

?

.~

v 7.0 SLB Leak Itate and Tube Burst Probability Analyses This section presents results of analyses carried out to predict leak rates and tube burst probabilities for postulated SLB conditions using the actual voltage distributions from EOC 7 inspection as well as for the projected EOC-8 voltage distributions. The methodology used in these analyses is described in Section 5.0.

SG C with the largest total number ofindicationa as well as indications ov:r 1 volt is expected to yield the limiting SLB leak rate and burst probability for Cycle 8.

)

7.1 Leak Hate and Tube Burst Probability for EOC 7 Analysea to calculata ECC 7 SLB leak rates and tube burst probabilities were performed using the actual bobbin voltage distributions presented in Table 61.

Results of Monte Ccrlo calculations are summarized on Table 71. A cemparison of

}

the EOC 7 actuais in Table 71 with the corresponding predictions performed during the EOC 6 inspection, presented in Reference 8 2, indicates the following, a)

With a POD of 0.6, SG-C was predicted to be the limiting steam generator for EOC 7 baued on a voltage distribution projection performed during the EOC 6 outage. SG C was confirmed to have the highest tube leak rate and burst probability based on actual EC bobbin measurements for EOC-7.

b)

Total number of indications found in the EOC 7 inspection fbr all SGs are well below their projection. The projected maximum volts match the actual EOC measured volts. With NDE uncertainties added, the peak measured voltage for SG A exceeds its projection by 0.2 volt which is negligibly small.

The peak measured voltage for the remaining three SGs are bounded by their projected value.

c)

Leak rate and tube burst probability predictions for the projected EGC-7 indication popuhdion distribution, based on the EOC-6 inspection data, are conservative compared to the corresponding values calculated using EOC-7 actual measured bobbin measurements for all.

d)

Leak rate and tube burst probabi;ity predictions for all four SGs based upon EOC-7 actual bobbin measurements are well within the allowable limits.

The EOC 7 predictions presented in Reference 8 2 utilized a conservative bounding growth distribution that envelopes Cycle 6 growth data for all four SGs. However, the WCAP-14277 methodology (Reference 8-3) uses a different approach for selecting growth distribution applicable to a SG in that it recommends using the larger of the SG-specific growth and the composite growth from all SGs. Per the S:\\ agic \\tgx97\\ EOC7mi doc

\\

7-1 l

O

,e bEo WCAP 14277 methodology, Cyde 6 composite growth distribution would be applied to SGs A and C and their own growth data for SGs B and D to perform the EOC-7 projections. To ensure that the EOC 7 projections based on growth distribution selected per the WCAP 14277 methodology would bound the leak and burst results for the actual measured EOC 7 voltago data, EOC 7 projections for the two SGs with the highest leak rate and burst probability based on actual voltage data (SGr A and C) were repeated using growth rates selected per the WCAP 14277 methodology. Growth data for both SGs A and C are bounded by the composite growth data. Projected EOC-7 leak and burst results for SGs A and C based on Cycle 6 composite growth data are shown in the bottom part of Table 71, and it is evident that these results also bound those based on the EOC-7 nctual measured voltage data. The WCAP 14277 method of selecting growth data is used for the EOC 8 projections presented in the next section.

In summary, actual measured EOC 7 bobbin voltage distributions for all SGs are below the corresponding projections obtained using the NRC mandated probability of detection of 0.6. Limiting values for SLB leak rate (9.7 x 104 gpm) and tube burst probability (3.1 x 104) obtained using the actual measured voltages are nearly three orders of magnitude below the allowable Cycle 7 SLB leakage limit of 5.0 gpm (raom temperature) and the NRC reporting guideline of 10-2 ry 'he tube burst probability.

7.2 Lenk Rate and Tube Hurst Probability for EOC 8 Calculations to predict SLB leak rate and tube burst probability for the limiting steam generator in South Texas Unit 1 at the EOC-8 condition were carried out usmg 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 7 actual voltages.

Projected results for EOC 8 conditions nie summarized on Table 7 2.

With a constant POD of 0.6, the limiting EOC-8 SLB leak rate projected is 5.3x104 gpm (room temperature), and it is predicted for SG C which has the largest number of indications returned to service for Cycle 8 operation. This limiting SLB leak rate value is about 3 orders of magnitude below the allowable SLB leakage limit for Cycle 8 of 5.0 gpm (room temperature). The limiting tube burst probability, 9.4x104,is predicted for SG A which had the largest indication found in the EOC 7 inspection; it is 2 orders of magnitude below the NRC reporting guideline of 10 2, With EPRI POPCD total number ofindications predicted are higher than those for POD =0.6. The reason for this is that below about 0.5 volt, the detection probability calculated from EC inspection data could be significantly below 0.6 as shown by the EPRI POPCD distribution in Table 61 and Figure 61. Nearly 80% percent of S.\\apeup97\\EoC790d doc 7-2 1

~

?

?/

l =

the indications returned to service for Cycle 8 operations are below 0.5 volt, Because oflarger number of EOC 8 indications predicted with EPRI POPCD, SLB leak rato and burst probability for SGs B and D based on EPHI POPCD are either equal to or slightly higher than those with POD =0.G.

In summary, SLB leak rates and tube burst probabilities predicted for EOC-8 are 3 to 10 times higher than obtained for the actual EOC-7 conditions, but they are still 2 or 3 orders of magnitude smaller than their respective limits.

t 8 \\apc\\tgx97\\EOC790d doc 7-3

O i'

0 1

Table 71 South Texas Unit.1 1997 EOC. 7 Outage Summary of Calculations of Tube Leak Rate und Burst Probability Based on Actual Bobbin Voltage. 250k Simulations SLB Steam Number Max.

Burst Probability Leak Generator POD ofIndi.

Volts 2)

Rate r

entionsm 1 Tube 1 or More (gpm)m Tubes EOC. 7 Projections Reported in Reference 8.2 A

l 0.6 285 1.8 3.7 x10 6 3.7 x10 6 2.1x104 B

0.6 205.3 1.9 3.3 x10 6 3.3 x10 6 1.7x104 C

0.6 732.7 2.1 8.3 x10 6 8.3 x10 6 7.5x104 D

0.6 472 2.1 7.8 x10 6 7.8 x10 6 6.9x104 EOC-7 Actuals A

1 201 2.0 3.1 x10 6 33 x10 6 5.0x104 B

1 154 1.2

<1.2 x10 6

<1.2 x10 6 1.0x104 C

1 488 2.0 3.1 x10 6 3.1 x10 6 9.7x104 D

1 309 1.3

<1.2 x10 6

<1.2 x10 6 2.0x104 EOC. 7 Projections Repeated Using WCAP.14277 (Reference 8,.3)

Methodology for Growth Selection A

0.6 285 1.8 6.6 x10 6 6.6 x10 6 1.1x104 C

0.6 732.7 2 72 1.0 x10-4 1.0 x10 4 4.3x104 Nutes:

(1) Number ofindications adjusted for POD.

(2) Voltages include NDE uncertainties from Monte Carlo analyses and exceed measured voltages.

(3) Equivalent volumetric rate at romi. temperature.

S.\\apc\\tgs97\\ EOC790d doc 7-4

n j

Table 7 2 South Texno Unit J September 1997 Outage Summary of Projected Tube Leak Rate and Burst Probability far EOC 250k Simulations SLB Steam No. of Max.

Burst Probability Rate Generator POD Indic-Voltsm I-ationsm 1 Tube 1 or More (gpm)*

Tubes EOC 8 PROJECTIONS A

0.6 335 2.3 9.4x104 9.4x10 5 3.2xWI

~

E 0.6 255 1.7 1x10-5 3.1x104 8.1x104

~

C 0.6 800 2.3 8.3x104 8.3x104 5

8 D

0.6 5?2 1.8 4.7x104 4.7x104

.ux107 A

POPCD 408 2.2 7.5x104 7.5x104 2.4x10 3 B

POPCD 325 1.7 3.3x104 3.3x10 5 1.1x10 3 C

FOPCD 1022 2.7 7.6x104 7.6x10 5 4.2x10-3 D

POPCD 664 1.8 4.7x10 5 4.7x10 5 2.1x10-3 Hutca (1) Nt.mber ofindications adjusted for POD.

(2) Voltages include NDE uncertainties hom Ah ate Cada analyses and exceed sneasured voltages.

(3) Equi"alent volumetric rate at room temperature.

k S:\\npc\\tgx97\\EOC790d. doc 7-5

3.0 References 8.1 NRC Generic Letter 95-05, " Voltage-Based Repair Criteria for the Repair l

of Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," USNRC Office of Nuclear Reactor Regulation, August 3,1995.

!0 8.2 Docuoent Identifier 51-1245664-00, " South Texas Unit-1 May 19961RE06 2 Day Report for Voltage-Based Repair Criterion for ODSCC at Tube Support Plates,", Framatomo Technologies, August 22,1996.

8.3 WCAP-14277, Revision 1, "SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections", Westinghouse Nuclear Services Division, December.1996.

I 8.4 EPRI Report NP 7480 L, Addendum 1, " Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternato repair Limits," Electric Power Research Institute, November, 1996 8.5 Letter from N. J. Liparulo, Westinghouse Electric Corporation, to w. f.

Russel, Office of Nuclear Reactor Regulation, Nuclear Regulatory Commission, CAW-97-935, dated February 28,1997.

8.6 Letter from B. W. Sheron, Nuclear Regulatory Commission, to A. Marion, F,

Nuclear Energy Institute, dated February 9,1996.

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