ML17333A276

DC Cook Unit 1 1995 Interim Plugging Criteria 90 Day Rept.

ML17333A276
Person / Time
Site:	Cook
Issue date:	12/31/1995
From:	WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
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ML17333A275	List: ML17333A274 ML17333A276
References
SG-95-12-010, SG-95-12-10, NUDOCS 9601250143
Download: ML17333A276 (48)

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SG-95-12-010 D. C. COOK UNIT 1 1995 INTERIM PLUGGING CRITERIA 90 DAY REPORT DECEMBER 1995 WESTINGHOUSE ELECTRIC CORPORATION ENERGY SYSTEMS BUSINESS UNIT NUCLEAR SERVICES DIVISION P.O. BOX 355 PITTSBURGH, PENNSYLVANIA 15230 960i250i43 960ii9 PDR P

ADOCK 050003i5 PDR

D. C. COOK UNIT 1 1995 INTERIM PLUGGING CRITERIA 90 DAY REPORT DECEMBER 1995 TABLE OF CONTENTS Glossary 1.0 Introduction 2.0 Summary and Conclusions 3.0 EOC-14 Inspection Results and Voltage Growth Rates 3.1 EOC-14 Inspection Results 3.2 Voltage Growth Rates 3.3 NDE Uncertainties III 4.0 Data Base Applied for IPC Correlations 5.0, SLB Analysis Methods 6.0 Bobbin Voltage Distributions 6.1 Probability Of Detection (POD) 6.2 Cycle Operating Time 6.3 Calculation of Voltage Distributions 6.4 Predicted EOC-15 Voltage Distributions 6.5 Comparison of Predicted and Actual EOC-14 Voltage Distributions 7.0 Tube Leak Rate and Burst Probabilities 7.1 Calculation of Leak Rate and Tube Burst Probabilities 7.2 Predicted and Actual Tube Leak Rate and. Probability of Burst for EOC-14 7.3 Predicted Tube Leak Rate and Burst Probability for EOC-15 8.0 References

GLOSSARY APC Alternate Plugging Criteria BOC Beginning of Cycle CPDF Cumulative Probability Distribution Function EFPD Effective Full Power Day EFPY Effective Full Power Year ECT Eddy Current Test EOC End of Cycle GPM Gallons per Minute INR Indication Not Reportable IPC Interim Plugging Criteria NDE Non Destructive Examination NRC Nuclear Regulatory Commision ODSCC Outside Diameter Stress Corrosion Cracking PI Potential Indication POD Probability of Detection PWSCC Primary Water Stress Corrosion Cracking RTS Return to Service SG Steam Generator SER Safety Evaluation Report RPC Rotating Pancake Coil SLB Steam, Line Break TSP Tube Support Plate

D. C. COOK UNIT 1 1995 INTERIM PLUGGING CRITERIA 90 DAY REPORT

1.0 INTRODUCTION

This report provides the D.C. Cook Unit 1 steam generator tube support plate (TSP) bobbin voltage distribution. summary, together with postulated Steam Line Break (SLB) leak rate and tube burst probability analysis results, in support of the implementation of a 2.0 volt Interim Plugging Criteria (IPC) for Cycle 15 as outlined in the NRC Draft Generic Letter, Reference 8.1. Calculations of leak rates and probability of tube burst are reported, based on actual End Of Cycle 14 (EOC-14) bobbin voltage distributions. Also provided are projections of bobbin voltage distributions, leak rates and burst probabilities for Cycle 15 operation. The methodology used in these evaluations is in accordance with the previously published Westinghouse technical report, Reference 8.2.

The application of the TSP Interim Plugging Criteria at D.C. Cook Unit 1 involves bobbin coil inspection of the tube bundle and plugging of > 2.0 volt TSP indications which are con6rmed by Rotating Pancake Coil (RPC) inspection results. Plugging of

> 5.6 volts TSP bobbin indications is required regardless of RPC inspection results.

Calculational results of predicted SG tube leak rate and probability of burst during a postulated SLB at EOC-15 are well below regulatory requirements as outlined in the NRC SER, Reference 8.3.

1-1

2.0

SUMMARY

AND CONCLUSIONS SLB leak rate and tube burst probability analyses were performed for the actual EOC-14 bobbin voltage distributions and. for projected for EOC-15 distributions at D.C. Cook Unit 1. SG 11 was found to be the limiting SG at EOC-14, with the highest number of indications, bobbin voltage amplitude and leak rate for the postulated SLB.

The tube burst probability at EOC-14 is low (1.9 E-05), with only one tube burst occurring (in SG 12) in separate calculations of 250,000 Monte Carlo simulations for each SG. SG 11 is predicted to be limiting at EOC-15, with the highest number of indications, bobbin voltage amplitude and leak rate for the postulated SLB. The tube burst probability at EOC-15 is low, varying between 1.9 E-05 and 3.1 E-05 between the four SGs. SLB leak rates for the actual EOC-14 and projected EOC-15 distributions are 0.23 and 0.70 gpm, respectively. These calculations demonstrate that IPC application at EOC-14 (actual distribution) and at EOC-15 (predicted for POD = 0.6) will satisfy NRC criteria for allowable leakage and burst probability.

A total of 597 bobbin indications (in the tubes in service during Cycle 14) were reported during the EOC-14 inspection. The highest bobbin voltage recorded during this inspection was 1.71 volts, so there are no indications above the 2.0 volt IPC repair limit and no tube had to be plugged because of ODSCC at TSP intersections.

Five of the 597 were RPC inspected, of which 3 were confirmed. Thirteen indications were removed Rom service, but none because of ODSCC TSP indications.

Accordingly, 584 of the 597 indications were returned to service for Cycle 15.

Sixty one of the 597 bobbin indications were > 1.0 volt and all were < 1.8 volts; four of the 61 were RPC inspected; two of these four were confirmed; one of these four was plugged for reasons other than ODSCC at TSPs.

SG ll was limiting at EOC-14 with 199 indications (in the tubes in service during Cycle 14), of which 2 were RPC inspected, with 1 confirmation. Twenty of the 199 indications were reported as > 1.0 volt and < 1.71 volts (the highest reported bobbin voltage during the outage). Two of the 199 indications were removed from service, for reasons other than ODSCC at TSP.

For the actual EOC-14 bobbin voltage distribution, the limiting SLB tube leak rate is calculated to be 0.23 gpm and the limitingtube burst probability is < 4.0 E-06 E-06 for SG ll (1.9 E-05 for SG 12), substantially lower than the D.C. Cook Unit 1 allowable SLB tube leakage limit and the NRC reporting guideline for the tube burst probability (Reference 8.3). These results of actual EOC-14 tube leak rate and burst probability are lower than the corresponding predictions (0.44 gpm and 1.9 E-05) performed at BOC-14, demonstrating the conservatism of the prediction methodology.

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During the outage, tubes previously plugged in accordance with prior repair criteria for ODSCC at TSPs were deplugged, inspected and either returned to service in accordance with IPC criteria or replugged. Accordingly, 39 such indications (23 with

> 1.0 V and < 1.7 V bobbin amplitude) were returned to service, for a total of 623 indications returned to service for Cycle 15 operation in accordance with IPC criteria.

(During this outage, an extensive parallel effort was conducted to reroll and return to service tubes previously plugged for PWSCC.)

Using the NRC criteria of POD = 0.6 to calculate the performance of the limiting SG during the next D.C. Cook Unit 1 operating cycle, the SLB tube leak rate is projected to be 0.70 gpm for SG ll and the tube burst probability is projected to be 2.9 E-05 for SG 13 at EOC-15. These results are much lower than the D.C. Cook Unit'1 IPC requirement for allowable tube leakage and the NRC guideline for tube burst probability; accordingly Cycle 15 operation of D.C. Cook Unit 1 is considered to be in compliance with requirements of the NRC SER of Reference 8.3.

2-2

3.0 EOC-14 INSPECTION RESULTS AND VOLTAGE GROWTH RATES 3.1 EOC-14 INSPECTION RESULTS In accordance with the IPC guidance provided by the NRC draft generic letter (Reference 8.1), the end of Cycle 14 (EOC-14) inspection of the D.C. Cook Unit 1 steam generators (SG) consisted of a complete 100% bobbin probe full length examination of all TSP intersections in the tube bundles of all four SGs. RPC examination was performed for all bobbin indications with amplitudes > 1.5 V. The NRC IPC criteria require that RPC confirmed indications of > 2.0 Vbobbin amplitude shall be plugged and that > 5.6 V bobbin amplitude shall be plugged. Since the highest bobbin indication reported during this inspection was 1.71 V, independent of RPC confirmation, none of the tubes that were in service during Cycle 14 required plugging for ODSCC at TSP intersections. During this outage, tubes previously plugged in accordance with prior repair criteria for ODSCC at TSPs were deplugged, inspected and either returned to service in accordance with IPC criteria or replugged.

A summary of ECT indication distributions for all steam generators is shown on Table 3-1. For those tubes that were in service for Cycle 14, Table 3-1 provides the number of Geld bobbin indications, the number of these field bobbin indications that were RPC inspected, the number of RPC confirmed indications, the number of indications in plugged tubes, the number of Cycle 14 in-service indications that remain active for Cycle 15, the indications recovered from deplugged tubes which were returned to service for Cycle 15, and the subsequent total indication population being returned to service (RTS) for Cycle 15 (BOC-15). Overall, the combined data for the D.C. Cook Unit 1 steam generators shows that:

Out of a total of 597 indications which were in-service during Cycle 14 and were identified during the EOC-14 inspection, 13 were removed, from service (for causes other, than ODSCC at TSP intersections), leaving 584 which were returned to service for Cycle 15. All RPC confirmed indications have bobbin amplitudes of < 1.8 volt.

Of the 597 indications, a total of 5 were RPC inspected. Three of the Gve were

> 1.5 V but < 1.8 V.

Of the 5 RPC inspected, a total of 3 were RPC confirmed.

Additionally, 39 indications &om deplugged tubes were recovered and returned to service, for a total of 623 indications returned to service for Cycle 15 operation in accordance with IPC criteria.

3-1

Review of Table 3-1 indicates that steam generator ll has more total as well as higher amplitude BOC-15 indications (a quantity of 211, with 26 indications > 1.0 volt) than any of the other three SGs, thereby it potentially willbe the limiting SG at EOC-15.

Figure 3-1 shows the actual bobbin voltage distribution for tubes that were in service during Cycle 14, as determined from the EOC-14 ECT inspection; note that SG 11 appears to predominate over the other three SGs. The largest bobbin indication found in the EOC-14 inspection was 1.71 volts in SG ll (shown in the 1.8 volt bin).

Figure 3-2 shows the distribution of the relatively small population of those EOC-14 indications which were plugged and taken out of service (for reasons other than IPC) and Figure 3-3 shows the bobbin voltage distribution of indications in service during Cycle 14 returned to service for BOC-15.

During the outage, tubes previously plugged. in accordance with prior repair criteria for ODSCC at TSPs were deplugged, inspected and, either returned to service in accordance with IPC criteria or replugged; a summary of these tubes is presented on Table 3-2. Accordingly, 39 such indications (23 with >1.0 V and < 1.7 V bobbin amplitude) in the four SGs were returned to service for Cycle 15 in accordance with IPC criteria. Figure 3-4 shows the bobbin voltage distribution for the deplugged indications which were returned to service for Cycle 15. Figure 3-5 shows the total indications (those continuing from Cycle 14 service and those deplugged at EOC-14) which were returned to service for Cycle 15.

The distribution of EOC-14 indications as a function of support plate elevation, summarized in Table 3-3 and shown on Figure 3-6, shows the predisposition of ODSCC to occur in the first few hot leg TSPs (515 of 597 indications occurred in the first two hot leg TSPs), although the mechanism does extend to higher TSPs. There were no bobbin indications reported in the cold leg. This distribution indicates the predominant temperature dependence of ODSCC at D.C. Cook Unit 1, similar to that observed at other plants.

3.2 VOLTAGE GROWTH RATES Average bobbin voltage growth rates for the D.C. Cook Unit 1 steam generators, shown on Table 3-4, provide a comparison of recent operating cycles. These results provide an interesting overview of the progress of IPC over the last five years. The increase in the number of indications with V < 0.75 (where the number of indications increases from 30 to 356 to 445 during Cycles 12, 13 and 14, respectively) is attributed to improved ECT practice. Over the 1990 - 1995 time period, the focus on 3-2

ECT, including equipment, standards and analyst guidelines and training, has resulted in more accuracy and discrimination of bobbin probe signals, so that more low voltage indications are being reported. The preponderance of PIs are at low voltage, with the attendant lower accuracy in voltage growth associated with differences between small absolute numbers. The trend in growth rates is not definitive, since all average growth rates are too small for meaningful trend analysis.

The average growth rate comparisons for each SG during Cycle 14 are summarized on Table 3-5. The average growth rates varied between 3.0% and 9.9%, between SGs, with an overall average of 5.1% per EFPY. The average growth for indications with a BOC bobbin voltage > 0.75 volt is 5.0% per EFPY and for indications < 0.75 volt is 5.8% per EFPY. SG 12 has the highest average voltage at BOC-14 whereas SG 11 has the largest average growth during Cycle 14.

Another cycle growth comparison is provided. in more detail by the Cumulative Probability Distribution Functions (CPDF) for Cycle 12, 13 and 14 data summarized on Tables 3-6, 3-7, and 3-8, respectively, and shown on Figure 3-7. There is a modest difference between Cycle 13 and 14 and the order of increasing cycle growth for the CPDF shown on Figure 3-7 agrees with the average ranking from Table 3-4. The NRC generic letter recommends that the more conservative growth distribution kom the last two cycles be used for projecting EOC distributions. Accordingly, the Cycle 14 bobbin voltage growth rates willbe used for prediction of EOC-15 conditions; these rates are developed from the 1995 EOC-14 inspection data and a reevaluation of the same indications from the previous (1994) inspection ECT signals.

Table 3-8 shows the Cumulative Probability Distribution Function (CPDF) for each SG during Cycle 14; the same data is presented in graphical form on Figure 3-8. For conservatism, a worst case hybrid growth distribution is defined on Table 3-8, which envelopes the actual EOC-14 distribution with the simultaneous limitations of SG ll (highest average growth and number of indications) and of SG 12 (highest voltage increment of 0.7 volt). This hybrid growth is imposed on all four SGs, to provide a conservative basis for predicting EOC-15 conditions.

The EOC-14 field bobbin data summarized on Table 3-1 (the basis for EOC-15 bobbin voltage and all tube leakage and burst probability calculations reported herein) does not include INR (Indication Not Reportable) field calls. Generally, growth estimates are calculated only for the cases where bobbin signal voltage is available for both inspections; i.e., no assumption about the signal voltage for prior year is made if a reliable Qaw indication is not available. However, new indications which were called INRs in the EOC-13 inspection were included in the growth analysis (and the bobbin voltage reported. at EOC-13 was used) as it results in slightly more conservative growth rates.

3-3

3.3 NDE UNCERTAINTIES The NDE uncertainties applied for the Cycle 15 voltage projections in this report are documented in References 8.2 and 8.4. 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 used to predict the EOC-15 voltage distributions.

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Table 3-1 D. C. Cook Unit 1 1995 EOC-14 Summary of Inspection anti Repair For Tubes in Service During Cycle 14 Steam Generator 11 Steam Generator 12 BOC-14 BOC-l5 EOC-14 BOC-l5 InScrvice During Cycle 14 InService During Cycle 14 Dcptuggcd All Dcplugged All Voltage Field Returned Tubes All Field Returned 1bbcs Vubcs Bin Bobbin Returned Rctumed Retumcd Returned Bobbin Indiications Savice Inpcctcd Savice Savice Savice Savice Savice 0.2 0.3 0.4 20 19 20 14 14 14 0.5 41 41 42 12 12 12 0.6 28 28 28 17 14 14 0.7 28 27 27 16 16 16 0.8 24 26 16 15 15 0.9 15 15 2 17 16 16 2 18 12 12 15 10 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Total 199 197 14 211 121 116 13 129

> 1V 20 20 26 16 15 10 25 Steam Generator 13 Steam Generator 14 BOC-14 BOG-15 EOC-14 BOC.I5 In-Service During Cycle 14 InSavice During Cycle 14 Depluggcd All Dcptuggcd All

%bcs All 'ltrbcs 'Itrbcs Voltage Rctumcd Returned Returned Field Retumcd Rcturncd Returned Bin Field Bobbin RPC RPC Indications to Bobbin to Indications Ins ted Confumcd R 'd Service Savice Savice Indications Indications R ared Savice Savice Savico 0.2 0.3 13 13 13 0.4 10 10 10 23 0 23 0 23 0.5 16 16 0 16 23 23 0 23 0.6 16 16 0 16 31 29 30 0.7 14 14 14 31 30 1 31 0.8 11 22 21 0 21 0.9 10 10 15 14 16 1.3 1.4 1.5 1.6 1.7 1.8 Total 90 90 94 187 6 181 8 189

) 1V 17 17 21

Table3-2 D. C. Cook Unit 1 1995 EOC-14 Summary of Inspection and Repair For Tubes Deplugged at EOC-14 Steam Generator 11 Steam Generator 12 Voltage Retumcd Field Retumcd Bin Field Bobbin RPC RPC to Bobbin Indications to Indications Ins tcd Confirmed Service Indications R Senicc 0.4 0.5 0.6 0.7 0.8 0.9 1.2 1.3 1.4 1.5 1.7 1.8 1.9 2.3 2.5 Total 15 14 20 13

>1V 7 17 10 Service

>2V Steam Generator 13 Steam Generator 14 Voltaac Returned Field Returned Bin Field Bobbm RPC to Bobbin RPC Indications to Indications Confirmed Indications Ins ctcd R Senicc 0.4 0.5 0.6 0.7 0.8 0.9 1.2 1.3 1.4 1.5 1.7 1.8 '0 1.9 2.3 2.5 Total

>1V 4

>2V 1

Table 3-3 D. C. Cook Unit 1 1995 Outage TSP ODSCC Indication Distributions for Tubes in Service During Cycle 14 Steam Generator 11 Steam Generator 12 Tub e Support Number Number Maximum Average Average Maximum Average Average Plate of of Voltage Voltage Growth Voltage Voltage Growth Indications Indications lH 133 1.71 0.68 0.065 58 1.59 0.72 0.056 2H 46 1.08 0.66 0.065 45 1.69 0.73 0.027 3H 15 0.59 0.064 0.7 0.50 0.015 4H 0.65 0.41 0.025 0.59 0.42 0.000 5H 0.54 0.46 -0.090 6H 0.36 0.36 -0.030 7H Total 199 121 Steam Generator 13 Steam Generator 14 Tube Number Number Support Maximum Average Average Maximum Average Average Plate of of Voltage Voltage Growth Voltage Voltage Growth Indications Indications 1H 59 1.18 0.64 0.035 81 1.46 0.69 -0.011 2H 24 1.4 0.65 0.028 69 1.36 0.64 0.048 3H 0.78 0.58 0.033 29 1.13 0.55 0.028 4H 0.69 0.47 0.072 5H 0.21 0.21 0.030 0.36 0.36 0.110 6H 0.36 0.36 0.100 Total 90 187 Composite of Ail Four SGs Tube Number Support Maximum Average Average Plate of Voltage Voltage Growth Indications 1H 331 1.71 0.68 0.039 2H 184 1.69 0.67 0.044 3H 58 1.13 0.56 0.033 4H 18 0.69 0.43 0.029 5H 0.54 0.37 -0.010 6H 0.36 0.36 -0.030 7H 0.36 0.36 0.100 Total 597

Table 3-4 D. C. Cook Unit-1 1995 Outage Average Voltage Growth History 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 Cycle 14 (1994 - 1995) - 390.54 EFPD Entire Volta e Ran e 597 0.62 0.034 0.031 5.4% 5.1%

Vqoo< .75 Volts 445 0.50 0.031 0.029 6.3% 5.8%

2 .75 Volts 152 0.94 0.050 0.047 5.3% 5.0%

Cycle 13 (1992- 1994) - 444.2 EFPD Entire Volta e Ran e 514 0.66 0.010 0.008 1.2% 1.0%

Vqoo< .75 Volts 356 0.50 -0 -0 -0% -0%

c .75 Volts 158 0.95 0.03 0.025 2.6% 2.1%

Cycle 12 (1990- 1992) - 455 EFPD Entire Volta e Ran e 201 1.00 0.020 0.016 1.6% 1.3%

Vqoo < .75 Volts 30 0.67 0.080 0.064 96% 7.7%

2 .75 Volts 171 1.07 0.010 0.008 0.8% 0.6%

Tablc3-5 D. C. Cook Unit -1 1995 Outage Average Voltage Growth During Cycle 14 Number of Average Voltage Average Voltage Growth Percent Growth Indications BOC Entire Cycle Per EFPY'ntire Cycle Per EFPY" Composite of All Steam Generator Data ntire Voltage Range 597 0.62 0.034 0.031 5.4% 5.1%

V aoc < .75 Volts 445 0.50 0.031 0.029 6.3% 5.8%

>.75 Volts 152 0.94 0.050 0.047 53% 5.p Steam Generator 11 ntire Voltage Range 199 0.60 0.064 0.059 1P6 99%

V soc < .75 Volts 156 0.52 0.051 0.047 98% 9.2%

2.75 Volts 43 0.90 0.110 0.103 12.3% 11.5%

Steam Generator 12 ntire Voltage Range 121 0.65 0.036 0.034 5.2%

Vaoc< .75 Volts 83 0.49 0.032 0.030 64% 60%

2.75 Volts 38 0.99 0.047 0.044 4.7% 44 Steam Generator 13 ntire Voltage Range 90 0.60 0.033 0.031 5.5%

V aoc < .75 Volts 70 0.50 0.029 0.027 59% 5.5%

2.75 Volts 20 0.95 0.046 0.043 4.8% 4.5%

Steam Generator 14 ntire Voltage Range 187 0.62 0.020 0.019 3.2% 30%

Vaoc< .75 Volts 136 0.50 0.026 0.024 48%

2.75 Volts 51 0.95 0.005 0.004 0.5% p.4 Based on Cycle 14 duration of 390.54 EFPD

Table 3 -6 D.C.Cook Unitl Signal Growth Statistics For Cycle 12 ('90 to '92) on EFPY Basis Delta Steam Generator 11 Steam Generator 12 Steam Generator 13 Volts No. of No. of No. of CPDF CPDF CPDF Obs Obs Obs 0.021 0.086 0.063 0.037 23 0.483 0.167 0.222 0.1 24 0.897 27 0.729 16 0.815 0.2 0.875 0.3 0.958 0.4 Total 58 48 27 Delta Steam Generator 14 Cumulative Volts No. of No. of CPDF CPDF Obs Obs 0.031 0.010 0.077 0.030 13 0.277 21 0.136 22 0.615 55 0.414 0.1 19 0.908 86 0.848 0.2 0.969 22 0.960 0.3 0.985 0.985 0.4 Total 65 198

Table 3 - 7 D. C. Cook Unit 1 Signal Growth Statistics For Cycle 13 ('92 to '94) on EFPY Basis Steam Generator 11 Steam Generator 12 Steam Generator 13 Volts No. of No. of No. of CPDF CPDF CPDF Obs Obs Obs 0.006 3 0.029 0.012 18 0.122 0.078 0.071 58 0.494 35 0.417 33 0.464 0.1 59 0.872 48 0.883 35 0.881 0.2 18 0.987 0.961 0.988 0.3 0.990 0.4 Total 156 103 84 Delta Steam Generator 14 Cumulative Volts No. of No. of CPDF CPDF Obs Obs 0.035 0.021

-0.1 10 0.094 38 0.095 71 0.509 197 0.479 0.1 70 0.918 212 0.891 0.2 14 49 0.986 0.3 0.998 0.4 Total 171 514

Table 3- 8 D. C. Cook Unit 11995 Signal Growth Statistics For Cycle 14 ('94 to '95) on an EFPY Basis Delta Steam Generator 11 Steam Generator 12 Steam Generator 13 Volts No. of No. of No. of CPDF CPDF CPDF Obs Obs Obs 0.017 0.035 0.066 0.022 57 0.322 0.455 32 0.378 0.1 81 0.729 45 0.826 41 0.833 0.2 36 0.910 12 0.926 13 0.978 0.3 13 0.975 0.975 0.4 0.985 0.983 0.5 0.995 0.992 0.6 0.992 0.7 Total 199 121 90 Delta Steam Generator 14 Cumulative Hybrid "

Volts No. of No. of No. of CPDF CPDF CPDF Obs Obs Obs 0.011 0.003 0.016 0.008 0.059 23 0.047 0.035 64 0.401 200 0.382 57 0.320 O.l 90 0.882 257 0.812 81 0.725 0.2 19 0.984 80 0.946 36 0.905 0.3 2 0.995 23 0.985 13 0.970 0.4 0.995 0.990 0.980 0.5 0.997 0.990 0.6 0.998 0.995 0.7 Total 187 597 200

" Growth distribution for SG-11 plus the largest growth observed, which is in SG-12.

Figure 3-1 D. C. Cook Unit -1 1995 Outage Bobbin Voltage Distributions for Tubes in Service During Cycle 14 45 40 35 HSG- 11 30 OSG- 12

~

O Pt

~ 25 HSG-13 O

c 20 SSG- 14 15 10 nl ca W m uo c oo m ~ ~ W m W m m t ao CD CD CD CD CD CD CD CD Bobbin Voltage

Figure 3-2 D. C. Cook Unit-1 1995 Outage Bobbin Voltage Distribution for Tubes Plugged After Cycle 14 Service HSG-11 CISG- 12 HSG- 13

~ SG- 14 0.4 0.6 0.7 0.8 0.9 Bobbin Voltage

Figure 3-3 D. C. Cook Unit -1 1995 Outage Bobbin Voltage Distributions for Tubes in Service During Cycle 14 and RTS for Cycle 15 45 40 35 BSG- 11 30 O

OSG- 12

" 25 IH HSG- 13 O

cp 20

~ SG- 14 15 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Bobbin Voltage

Figure 3-4 D. C. Cook Unit -1 1995 Outage Bobbin Voltage Distributions for Deplugged Tubes Returned to Service for Cycle 15 Operation HSG-11 OSG-12 BSG-13

~ SG- 14 0.4 0.5 0.6 0.7 0.8 0.9 1.1 1.2 1.3 1.4 1.5 1.7 Bobbin Voltage

Figure 3-5 D. C. Cook Unit -I 1995 Outage Bobbin Voltage Distributions for All Tubes Returned to Service at BOC-15 45 40 35 HSG- 11 30 O

OSG- 12

~ Pt

~ 25 HSG- 13 O

cj 20

~ SG- 14 15 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Bobbin Voltage

Figure 3- 6 D. C. Cook Unit 1 1995 Outage ODSCC Axial Distributions for Tubes in Service During Cycle 14 140 120 100-Ch O

OH QSG- 11 80 O

HSG-12 60 8 HSG- 13 K

SSG-14 40 20 Tube Support Plate

Figure 3-7 D. C. Cook Unit-1 Cumulative Probability Distributions for Voltage Growth History on an EFPY Basis Composite of All Four Steam Generators 1.0 0.9 P r d,'

~

O.S

~

'"O 0.7

~ 0

~ ~

--+--Cycle 14 g 0.6 I;

i

~ 0.5

~

~

I -->- Cycle 12 Ie

~

~ ~

.g 0.4 Cycle 13 N03 U

0.2

~

.d: ~

0.1

~

t y o

0.0

-0.5 -0.4 -0.3 -0.2 -0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Voltage Growth

Figure 3-8 D. C. Cook Unit -1 Cycle 14 ( 1994 to 1995 )

Cumulative Probability Distributions for Voltage Growth on EFPY Basis 1.0 0.9 0.8

- 0.7 ~SG11 0

O P\

0.6 ~SG 12 1= 0.5 ~SG 13 04 ~SG14

~- Cumulative m 0.3 0.2 0.1 0.0 Vl CO CO I I Voltage Growth

4.0 DATA BASE APPLIED FOR IPC CORRELATIONS The database used for the IPC correlations that are applied in the analyses of this report are consistent with the NRC SER applicable to the D.C. Cook Unit 1 EOC-14 inspection (documented in Reference 8.3). The SER recommended data for the burst pressure correlation is the same as the EPRI recommended database described in Reference 8.4 and is applied in the analyses of this report.

For the SLB leak rate correlation, the NRC recommends that Model Boiler specimen 542-4 and Plant J-1 pulled tube R8C74, TSPl be included in the database. This database is referred to as the NRC database in Reference 8.5 (WCAP-14123) and is applied for the leak rate analyses of this report. The probability of leakage correlation of Reference 8.5 (WCAP-14123) is also accepted by the NRC SER and applied in this report. The SLB leak rate data do not satisfy the NRC guidelines for a voltage dependent correlation and, consistent with GL-95-05, the leak rate correlation is developed. independent of voltage, as discussed in Section 5.

Correlations have been developed for the evaluation of ODSCC indications at TSP locations in steam generators of nuclear power plants which relate bobbin voltage amplitudes, free span burst pressure, probability of leakage'and associated leak rates.

The Westinghouse methodology used in the calculation of these parameters, documented in References 8.2 and 8.5, is consistent with NRC criteria and guidelines of References 8.1 and 8.3.

The analysis process starts with the receipt of bobbin voltage from the site ECT inspection team. The site data consists of electronic files which include Row, Column, TSP identification number, and bobbin voltage. This data, sorted by bobbin voltage into "voltage bins" consisting of number of indications in discrete voltage ranges in increments of 0.1 volt, constitutes one major component of input for the subsequent voltage distribution, leak and burst probability calculations. It is noted that reference to "volts" in this report invariably applies to "voltage bins", when cited to one significant figure after the decimal (e.g., 1.8 volts). The true value of an indication would be cited to two significant figures after the decimal (e.g., 1.71 volts).

The calculation consists of determining the initial conditions (i.e., the bobbin indication population distribution), projecting the indication growth over the operating period, and then evaluating the tube leak and burst probabilities at the end of the operating period. Since indication growth is considered proportional to operating time, the limiting tube conditions occur at the end of any given time period or cycle.

4-1

5.0 SLB ANALYSIS METHODS Monte Carlo analyses are used. to predict the EOC-15 voltage distributions and to calculate the SLB leak rates and tube burst probabilities for both the actual EOC-14 voltage distribution and the predicted EOC-15 voltage distribution. These methods are consistent with the requirements of the D.C. Cook Unit 1 NRC SER and are described in the generic methods report of WCAP-14277 (Reference 8.2) and the IPC report of WCAP-14123 (Reference 8.5).

Based on the NRC SER recommended leak rate database, the leak rate data do not satisfy the requirement for applying the SLB leak rate versus bobbin voltage correlation. The NRC requirement is that the p value obtained from the regression for the slope parameter be less than or equal to 5%. For the NRC recommended data, the p value is about 6.5% and the leak rate versus voltage correlation is not applied.

The SLB leak rate correlation applied is based on an average of all leak rate data independent of voltage. The analysis methods for applying this leak rate model are given in Section 4.6 of WCAP-14277. A Monte Carlo analysis is applied to account for parameter uncertainties even though the leak rate is independent of voltage. This method of leak rate analysis is similar to that of draft NUREG-1477 except for the uncertainty treatment.

5-1

6.0 BOBBIN VOLTAGE DISTRIBUTIONS 6.1 PROBABILITY OF DETECTION (POD)

The number of bobbin voltage indications used to predict tube leak rate and burst probability is obtained by adjusting the number of reported indications to account for measurement uncertainty and confidence level in voltage correlations. This is accomplished by using a Probability of Detection (POD) factor. Adjustments are also made for indications either removed from or returned to service. The calculation of projected bobbin voltage frequency distribution is based on a net total number of indications returned to service, defined as:

N,.

NTot RTS Repaired deplugged r where:

NTot RTS Number of bobbin indications being returned to service for the next cycle.

N; Number of bobbin indications (in tubes in service during the previous cycle) reported in the current inspection.

POD Probability of Detection.

repaired Number of N; which are repaired (plugged) after the last cycle.

deplugged Number of previously-plugged indications which are deplugged after the last cycle and are returned to service.

The NRC generic letter (Reference 8.1 is the draft of GL-95-05) requires the application of a POD = 0.6 to define the BOC distribution for the EOC voltage projections, unless an alternate POD is approved by the NRC.

6.2 CYCLE OPERATING TIME The operating periods used in the voltage projection calculations are:

Cycle 12 = 455. EFPD. Cycle 13 = 444.2 EFPD. Cycle 14 = 390.54 EFPD.

Cycle 15 = 425. EFPD (Normal Burnup) or 465. EFPD (With Power Coastdown).

6.3 CALCULATIONOF VOLTAGE DISTRIBUTIONS Bobbin voltage projections start with a cycle initial voltage distribution which is projected to the corresponding cycle final voltage distribution, based on the growth rate adjusted for the anticipated cycle operating time period. The overall growth rates for each of the D.C. Cook Unit 1 steam generators during the previous two operating periods, as represented by their cumulative probability distribution 6-1

functions, are shown on Figure 3-7. The 1994 - 1995 operation (Cycle 14) growth rates exceed those of the 1993 - 1994 (Cycle 13) operation and. are used to predict the EOC-15 bobbin voltage distributions. Further conservatism for the EOC-15 bobbin voltage prediction is provided by the use of a limiting voltage growth hybrid envelope described in Section 3.2, for the voltage projections of each SG. The methodology used in the calculations of EOC bobbin voltage distributions is described in References 8.2 and 8.4.

For each SG, the initial bobbin voltage distribution of indications being returned to service for the next cycle (BOC-15) is derived from the actual EOC-14 inspection results adjusted for tubes that are either (a) taken out of service by plugging, or (b) have been recovered for Cycle 15 service by deplugging of tubes plugged in previous outages on the basis of prior repair criteria. The Cycle 15 bobbin voltage population, summarized on Table 6-1, shows EOC-14 bobbin voltage indications; the subsequent plugged indications (which were in service for Cycle 14 and then taken out of service, albeit not for reasons of ODSCC at TSP); those indications recovered for service from previously plugged tubes, which were deplugged during this outage and were inspected and returned to service in accordance with IPC criteria (otherwise they were replugged); and also shows the BOC-15 indications corresponding to PODs of 0.6, 1.0, and the EPRI lower 95% confidence limit.

6.4 PREDICTED EOC-15 VOLTAGE DISTRIBUTIONS Calculation of the predicted EOC-15 bobbin voltage distributions is performed for all SGs with three different detection factors represented by:

POD = 0.6, in accordance with NRC direction.

POD = EPRI, a voltage based probability developed by EPRI.

POD = 1.0, a nominal value with no uncertainty considered.

Using the methodology previously described, analyses were performed to predict the performance of the D.C. Cook Unit 1 steam generators at EOC-15, based on the BOC-15 summarized in Table 6-1 and the Cycle 14 hybrid growth distribution summarized in Table 3-8 (in accordance with NRC guidelines, Cycle 14 growth is used since it is the higher of the last two cycles). The EPRI developed voltage dependent POD is based on expert opinion and multiple analysts'valuations for plants with 3/4" diameter tubes. It is of interest to apply the EPRI POD for sensitivity analysis and for comparison with POD = 0.6 and POD = 1.0. The BOC-15 IPC voltage distributions are summarized on Table 6-1 for POD = 0.6, for the EPRI POD and for POD = 1.0, which is the order of decreasing detection uncertainty. The corresponding EOC-15 predicted IPC voltage distributions are summarized on Table 6-2

6-2. The POD = 0.6 is sufficiently small to conservatively account for both undetected and new indications formed during the next operating cycle. Since the net adjustment from the POD is applied to obtain the BOC distribution, the number of indications does not further increase over the operating cycle. As anticipated, the limiting steam generator is SG 11 with 344 indications predicted for POD = 0.6. For each steam generator, the BOC-15 actual and the EOC-15 predicted bobbin voltage frequency distributions are shown on Figure 6-1, 6-2, 6-3, and 6-4, respectively, for all three PODs. The maximum bobbin voltage predicted for EOC-15 is 2.4 V for POD = 0.6, in SG ll and SG 12.

6.5 COMPARISON OF PREDICTED AND ACTUALEOC-14 VOLTAGE DISTRIBUTIONS The actual EOC-14 bobbin voltage distributions and the corresponding predictions, summarized on Table 6-3 and shown on Figures 6-5 and 6-6, provide a comparison of detection probability factors represented by the two PODs used in the EOC-14 predictions. As reported in Reference 8.6, SG 14 was predicted to be limiting for EOC-14. As shown on Figure 6-5, the POD = 0.6 calculation overpredicted the actual SG 14 EOC-14 bobbin voltage population distribution, except for the 0.3 and 0.4 volt bins where the population was underpredicted. As shown on Figure 6-6, the POD = 1.0 calculation underpredicted the actual bobbin voltage population distribution in five out of six bins below 0.8 V and over-predicted in eight out of ten above 0.8 V. The overprediction in the higher volt range demonstrates the conservatism in the growth rate distribution used for the prediction. The predicted bobbin voltages of 2.0 V and 1.9 V for POD = 0.6 and 1.0, respectively, are conservative relative to the actual measured bobbin voltage indication of 1.5 V in SG 14. The actual EOC-14 bobbin voltage for SG ll, which turned out to be the limiting SG at EOC-14 by a small margin, is also shown on Table 6-3 and on Figure 6-5 and Figure 6-6.

6-3

TABLE 6-1 D. C. Cook Unit 1 1995 Outage Summary of Inspection and Repair of Tubes STEAM GENERATOR 11 STEAM GENERATOR 12 EOC-14 BOC.15 EOC-1 4 BOC-16 Voltage Field Plug Deplug POD POD= POD Field Plug Deplug POD POD= POD Bin In* Ind. RTS W.6 EPRI =I.O Ind. Ind. RTS EPRI =I.O 0.10 0.0 0.0 0.0 0.0 0.20 3.3 6.3 5.0 9.4 0.30 8.3 11.6 13.3 18.6 0.40 20 33.3 37.0 20 14 23.3 25.9 14 0.50 69.3 70.9 42 12 20.0 20 ' 12 0.60 28 46.7 44.2 28 17 25.3 23.8 14 0.70 28 45.7 40.2 27 16 26.7 23.5 0.80 24 42 ' 34.9 26 16 25.7 20.9 0.90 15 27.0 21.2 11.7 9.0 1.00 16 28.7 21.7 18 12 23.0 17.8 15 1.10 16.0 11.7 10 11.0 8.1 1.20 9.7 7.6 3.7 3.1 1.30 5.0 3.3 3.3 2.2 1.40 3.3 2.2 6.7 4.3 1.50 2.7 2.1 7.7 7.1 1.60 0.0 0.0 1.7 1.70 1.0 1.0 1.7 1.0 1.80 1.7 1.0 0.0 0.0 TOTAL 14 344 317 211 121 13 210 196 129

>1V 20 39 29 26 16 10 19 27 25 STEAM GENERATOR 16 STEAM GENERATOR 14 EOC 14 BOG.15 EOC.14 BOC 15 Voltage Field Plug Deplug POD POD= POD Field Plug Deplug POD POD= POD Bin Ind. Ind. RTS W,6 EPRI =1.0 Ind. Ind. RTS W.6 EPRI =1.0 0.10 0.0 0.0 0.0 0.0 0.20 1.7 3.1 1.7 3.1 0.30 6.7 9.3 13 21.7 30.2 13 0.40 10 16.7 18.5 10 38.3 42.6 23 0.50 16 26.7 27.3 16 23 38.3 39.2 23 0.60 16 26.7 25.3 16 31 50.7 47.9 30 0.70 14 23.3 20.6 14 31 51 ' 45.6 0.80 18.3 15.1 22 35.7 29.1 21 0.90 5.0 3.8 17.3 13 ~ 1 10 1.00 12.7 9.6 15 26.0 19.5 1.10 1.7 1.2 12.0 9.1 1.20 10.3 7.7 8.3 5.7 1.30 1.7 4.3 3.2 1.40 2.7 2.1 5.0 3.2 1.50 0.0 0.0 2.7 2.1 1.60 0.0 0.0 0.0 0.0 1.70 0.0 0.0 0.0 0.0 1.80 0.0 0.0 0.0 0.0 TOTAL 90 154.2 144.7 94.0 187 3'l3.7 293.6 189.0

>1V 16 12 17 32

TABLE 6-2 D. C. Cook Unit 1 1995 Outage Summary of Predicted Bobbin Voltage Distributions for EOC-15 STEAM GENERATOR II STEAM GENERATOR l2 Voltage Bin POD a 0.6 POD a EPRI POD < I.O POD n 0.6 POD a EPRI POD a I,O 0.1 0.1 0.1 0.0 0.1 0.2 0.1 0.2 1.7 3.1 1.0 2.6 4.7 1.6 0.3 6.1 8.5 3.7 8.1 11.6 4.8 0.4 20.5 23.4 12.3 14.8 18.0 8.9 0.5 39.4 41.4 18.5 20.4 11.0 0.6 46.1 46.0 27.8 21.6 21.7 '12.6 0.7 45.7 43.0 27.5 23.5 21.9 13.7 0.8 42.0 37.4 25.4 22.8 20.1 13.4 0.9 36.0 30.5 22.1 20.6 17.3 12.3 1.0 29.6 24.'I 18.4 17.9 14.5 11.0 23.1 18.3 14.5 14.5 11.5 9.1 1.2 17.0 13.2 10.8 8.7 7.1 1.3 12.0 9.3 7.7 8.5 6.5 5.6 1.4 8.2 6.3 5.3 6.7 5.2 4.6 1.5 5 ~5 4.1 3.6 5 ' 4.3 3.9

'1.6 3.7 2.7 2.4 4,4 3.4 3.1 1.7 2.5 1.8 3.2 2.5 2.3 1.8 1.7 1.2 1 ~ 1 2.2 1.7 1.6 1.9 0.8 0.8 1.4 1 ~1 1.0 2.0 0.7 0.3 0.3 0.8 0.5 0.4 2.1 0.1 0.0 0.0 0.1 0.0 0.0 2.2 0.7 0.7 0.7 0.7 0.7 0.7 2.3 0.0 0.3 0.3 0.0 0.3 0.3 2.4 0.3 0.0 0.0 0.3 0.0 0.0 TOTAL 344 317 211 210 196 129

>1V 59 49 59 46 40 SIAM GENERATOR 13 SIAMGENERATOR 14 Voltage Bin POD a 0.6 POD a EPRI POD a I.O POD a 0.6 POD ~ EPRI POD a LB 0.1 0.0 0.1 0.0 0.0 0.1 0.0 0.2 0.9 1.7 0.6 1.5 2.4 0.9 0.3 4.1 5.6 2.4 11.2 15.2 6.7 0.4 10.4 12.1 6.2 23.7 28.1 14.2 0.5 17.7 18.8 10.6 32.7 35.4 19.6 0.6 21.9 21.8 13 ~ 2 40.5 40.4 24.1 0.7 22.2 20.9 13.3 43.4 40.6 25.9 0.8 19.2 17.2 11.5 39.1 34.8 23.3 0.9 14.8 12.7 9.0 31.9 27.1 19.0 1 ~ 0 11.3 9.3 6.9 25.3 20.5 15.2 1 ' 8.9 7.0 5 ' 19.3 15.2 11.8 1.2 7.0 5.5 4.5 14.3 8.8 1.3 5.4 4' 3.5 10.4 7.9 6.5 1.4 3.9 3.0 2.6 7.3 5.5 4.6 1 ~ 5 2.6 2.0 1.7 5.0 3.7 3.2 1.6 1.6 1.2 3.3 2.4 2.1 1.7 0.9 0.5 0.4 2.0 1.5 1 ~ 3 1.8 0.1 0.0 0.0 1.2 0.9 0.8 1.9 0.7 0.7 0.7 0.5 0.1 0.0 2' 0.0 0.3 0.3 0.0 0.7 0.7 2.1 0.3 0.0 0.0 0.7 0.0 0.0 2.2 0.0 0.0 0.0 0.3 0.3 0.3 TOTAL 154 145 94 314 294 189

>1V 32 24 20 49 40

Table 6-3 D.C. Cook Unit 1 1995 Outage Comparison Of Predicted And Actual EOC-14 Bobbin Indication Population Number Of Indications Voltage SG 14 SG 11 Bin Predicted (Reference 8.6) Actual Actual POD = 0 6 POD = 1 0 0.1 0.2 0.3 13 0.4 20 12 23 20 0.5 19 23 0.6 36 21 31 28 0.7 40 24 28 0.8 '37 22 22 24 0.9 30 18 15 1.0 25 14 15 16 1.2 13 1.3 1.4 1.6 1.7 1.8 0.7 1.9 0.7 0.3 2.0 0.3 TOTAL 278 163 187 199 6-6

Figure 6-1 D. C. Cook Unit 1 Steam Generator 11 Bobbin Voltage Distributions for Cycle 15 70 POD = 0.6 0 Actual BOG.15 0 Predcted EOG-15 50 40 4

30 10 o

o ft o g o

0o 8 o

8o o do8 o

8 0 i oi 8 R'. g Bebbin Veltege i i Q $! 8' o 8 i 8 8 et o

el R

ee 8

el o

er POD = EPRI 70 OActett BOC-15 4

4 50 ~ Predcted EOC.15 4

50 e 40 4

30 E

Z 20 10 0

o 0 0 0 0 0 8o R o 8o 8 o 8 a -w g gw + ag 8' 4 lit

+ 8 N et 8

N N N Bebbln Veltege 45 POD >1.0 OActrtetBOC 15 35

~ Prectcted EOC.1S 30 25 4 20 I 1S 10 8 g0 0 g 8O R 8 8 8 0 R tPt 0' g 8' 0 8 til 8 0 R 0 0 O O ~ N rJ N re 44 Bebbln Veltege

Figure 6-2 D. C. Cook Unit 1 Steam Generator 12 Bobbin Voltage Distributions for Cycle 15 POD = 0.6 25 o 0Actuat BOC.15 C

=: 20 ~ Predcted EOC 15 15 o

10 I

R 5

0 0 0 0 0 8

0 o

0 8 o 8 d 8 -

v R

~ $

v j 0e g

~

8 R 8

~ tit

~ 8 ri N 8

N 8

re o

cd Bobbin Voltage POD = EPRI 25 0 Actual SOC.15 n ~ Predcted EOC.15 o 20 B

15 ri

~ 10

?

5 o

d g o o5t o

o 8 R 8 o

8 o 8' - g

~ g Bobbin Voltage Q g 8' R

>>'8 g lit ci ot oa or ci 16 POD -1.0 0 Actual BOC.1 5 o 14 C B Predcted EOC.15 12 B

10 6

0 0 0ft, R0 8 ~0 R 8 8, ft g Bobbin Voltage 0 Q 8 R g hatt 8

Figure L3 D. C. Cook Unit 1 Steam Generator 13 Bobbin Voltage Distributions for Cycle 15 POD = 0.6 25 D Actual BOC 15 c

= 20 B Predcted EOC-15 V

'D 15 0

'l0 I

0 0

g 0

80 00~

0 8

0 8

0 00r-0 8

0 til 0 8r - gr qr Q r

g 8 r' r-r titr foal 8 N Or Ot Bobbin Voltage POD 0farlEPRI 0 Actual BOC.15 c ~ Predctad EOC.15 20 o

15 o

~

?I 10 0

R 0 R 0

0 0 0 8

0 0

0 8

0 8

0 8r 0 r g Bobbin Voltage r

g 0r gr 8 '>>R Q 8N 0 Ot 8Ot POD = 1.0 le 0 Actual BOC.15 14

~ Predcted EOC.15 12 4 10 5

?

I 0

0 8 R 8 R 8 g g 0 g 8 R tii lit 8 - R Bobbin Voltage

Figure $ 4 D. C. Cook Unit 1 Steam Generator 14 Bobbin Voltage Distributions for Cycle 15 POD = 0.6 a Actual 8OC-15 C

o eo 8 Predcted EOC-15 o

30 o

10 0 0 80 0 g 8 R 8 8 8 -. g g 0v gs 8 8 g 8 8 ct 0 0 0 0 0 ~ ~ ~ ~

aobbln Yokemate POD n EPRI aActuet BOC 15 e0 0 Redcted EOC.15 o 55 u 30 25

~ 20 15 10 5

0 C>

o 0 8

0 o.

0 8 ct S

0 r

8 t:'

eobbinVokese 8 - 8 r 8

~

- 0 8 8 ru a Actuet eOC-1S c 25 8 Redctecl EOC 15 20 o 15 10 8 Q g 8 R 8 lit 8 -. g g 0 g 8 f' 8 8 Q~

Bobbin Vokege

Figure 6-5 D.C. Cook-1 EOC-14 Comparison of Actual vs. Predicted (POD=0.6) Bobbin Voltage Distributions 45 40 35

~SIG 11 EOC-14 Actual 30 lh S/G 14 EOC-14 Actual C

O

~~ 25 V

'a C

o 20 0

z 15 10 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 Volts

Figure 6-6 D.C. Cook-1 EOC-14 Comparison of Actual vs. Predicted (POD=1.0) Bobbin Voltage Distributions 45 40 35

~S/G 11 EOC-14 Actual 30 LO C

S/G 14 EOC-14 Actual S/G 14 EOC-14 Prediction (POD = 1.0) 25

'a C

o 20 0

15 10 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 Volts

7.0 TUBE LEAK RATE AND TUBE BURST PROBABILITIES 7.1 CALCULATIONOF LEAK RATE AND TUBE BURST PROBABILITIES Correlations have been developed for the evaluation of ODSCC indications at TSP locations in steam generators of nuclear power plants which relate bobbin voltage amplitudes (either measured or calculated), free span burst pressure, probability of leakage and associated leak rates. The Westinghouse methodology used in the calculation of these parameters, documented in References 8.2 and 8.4, is consistent with NRC criteria and guidelines of References 8.1 and 8.3.

7.2 PREDICTED AND ACTUAL LEAK RATE AND TUBE BURST PROBABILITYFOR EOC-14 Using the methodology previously described, analyses were performed to calculate EOC-14 SLB tube leak rate and probability of burst for the actual bobbin voltage distribution at EOC-14 (with no growth projection applied) previously presented in this report. The results of Monte Carlo calculations performed for the actual voltage distributions are compared to the prior prediction reported in Reference 8.6, as shown on Table 7-1. Comparison of the EOC-14 actuals with the corresponding predictions indicates that:

a) SG 14 was predicted to be the most limiting steam generator for Cycle 14.

b) Based on actual ECT bobbin measurements at EOC-14, SG ll has slightly more total (199 vs 187) as well higher amplitude (2.1 V vs 1.8 V) indications than SG 14.

c) Similarly, the SG ll tube leak rate (0.23 gpm) during a postulated SLB at EOC-14 is lower than predicted for the required POD=0.6 for SG 14 (0.44 gpm),

although the distinction is not significant at such low leakrates. The SLB leak rate of 0.23 gpm calculated Rom the actual EOC-14 voltage distribution is well below the D.C. Cook Unit 1 allowable limit of 12.6 gpm.')

The EOC-14 probability of burst prediction of 1.9 E-05 (1.6 E-03 for previously used different database) is conservative compared to that based on actual ECT bobbin measurements (< 4.0 E-06) and well below the NRC reporting threshold of 1.0 E-2.

Table 7-1 includes a current recalculation of the EOC-14 prediction (which was performed in the spring of 1994) using the same initial (input) conditions as in 1994 current methodology and database. The methodology of Reference 8.6 used in the

'ut original EOC-13 prediction has been enhanced by methods development represented by Reference 8.2. In addition, the database for the recalculation uses the current NRC approved data and exclusion criteria. This database and methods are consistent 7-1

with that applied for the actual EOC-14 analyses. Comparing the 1994 and 1995 EOC-14 predictions, the tube burst probability has decreased from 1.6 E-03 to 1.9 E-05 and the leakage has increased from 0.11 gpm to 0.44 gpm. The updated predictions are conservative relative to the actual EOC-14 results for SG 14.

e) Overall, the EOC-14 predictions based on POD = 1.0 are more accurate than those based on POD = 0.6, when compared to the results based on actual EOC-14 conditions. This suggests that a voltage based POD could more reliably predict tube leakage and probability of burst than a constant value of POD.

7.2 LEAK RATE AND TUBE BURST PROBABILITYFOR EOC-15 Using the methodology previously described, calculations have been conducted to predict the performance of the limitingsteam generator in D.C. Cook Unit 1, with the bobbin voltage distributions predicted for EOC-15. Results of the EOC-15 predictions, summarized on Table 7-1, indicate that there are not major differences between the four steam generators during postulated SLB conditions, due to the fact that tube leak rate and burst probability calculational results are low. As shown on Table 7-1, the maximum difference in predicted EOC-15 SLB tube leakage between the four SGs is less than 0.50 gpm, at a given POD. The corresponding range in number of single tube bursts, for all four SG and for all three PODs, varies kom one to three, in 250 k Monte Carlo simulations, as shown on Table 7-1. These differences are within the variability between Monte Carlo runs and are not meaningful for the small burst probabilities.

The limiting steam generator for Cycle 15 at D.C. Cook Unit 1 is expected to be SG ll. With the NRC endorsed POD = 0.6, the predicted EOC-15 SLB leak rate for SG ll is calculated as 0.70 gpm, whereas SG 14 produces 0.59 gpm. The EOC-15 SLB tube burst probability for SG 13 is calculated as 2.9 E-05, whereas SG 14 produces 2.7 E-05. These results are well below the D.C. Cook Unit 1 allowable SLB limit of 12.6 gpm'nd the NRC reporting guideline for tube burst probability of 1.0 E-02.

An ongoing analysis indicates that the maximum leakage (associated with the off-site dose) may be reduced f'rom 12.6 gpm by about a third, which is still weH above the projected SLB IPC leakage and still readily satis6es NRC criteria for IPC.

7-2

Table 7-1 D.C. Cook Unit 1 1996 Outage Summary of SLB Tube Leak Rate and Burst Probability 260,000 Simulations Steam POD No. of Max.'olts Burst Probability SLB Generator Indic- Leak Rate ations 1 Tube ; Occurences > 2 Tube gpm EOC-14 PREDICTED 0.6 278. 2.0 1.6 E-03 0.11 14 1.0 163. 1.9 14 alcaic 0.6 277. 2.0 1.9 E.05; 1 <4 E-06 0.44 1.0 163. 2.0 1.9 E-05; 1 < 4 E-06 0.22 EOC-14 ACTUAL 1.0 199. 2.1 <4.0E-06; 0 < 4.0 E-06 0.23 12 1.0 121. 2.0 1.9E-05; 1 < 4.0 E.06 0.14 13 1.0 90. 1.7 <4.0E.06; 0 < 4.0 E-06 0.06 14 1.0 187. 1.8 < 4.0 E-06; 0 < 4.0 E.06 0.20 EOC-16 PREDICTED 0.6 344. 2.4 1.9 E-05; 1 < 4.0 E.06 0.70 EPRI 317. 2.3 1.9 E.05; 1 < 4.0 E-06 0.57 1.0 211. 2.3 2.5 E-05; 2 < 4.0 E-06 0.42 12 0.6 210. 2.3 E-05; 1.7 < 4.0 E-06 0.50 12 EPRI 196. 2.3 2.5 E-05; 2 < 4.0 E.06 0.39 12 1.0 129. 2.3 3.1 E-05; 3 < 4.0 E-06 0.29 13 0.6 154. 2.1 2.9 E.05; 2.7 < 4.0 E-06 0.24 13 EPRI 145. 2.0 2.5 E-05; 2 < 4.0 E-06 0.19 13 1.0 94. 2.0 2.5 E-05; 2 < 4.0 E-06 0.12 14 0.6 314. 2.2 2.7 E.05; 2.3 < 4.0 E.06 0.59 14 EPRI 294. 2.2 1.9E-05; 1 < 4.0 E-06 0.47 14 1.0 189. 2.2 2.5 E-05; 2 < 4.0 E-06 0.33

'oltages include NDE uncertainties from Monte Carlo analyses and exceed measured voltages.

7-3

8.0 REFERENCES

8.1 Draft NRC Generic Letter 95-XX, "Voltage-Based Repair Criteria for the Repair of Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking", USNRC OKce of Nuclear Reactor Regulation, August 1994.

8.2 WCAP-14277, "SLB Leak Rate and. Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections", Westinghouse Nuclear Services Division, January 1995.

8.3 U.S. N.R.C. Report, "Safety Evaluation by the OKice of Nuclear Reactor Regulation Related to Amendment No. 200 to Facility Operating License DPR-58 Indiana Michigan Power Company Donald C. Cook Nuclear Plant, Unit No. 1 Docket No. 50-315", September 13, 1995.

8.4 WCAP-13187 (SG-92-03-005), "D.C. Cook Unit 1 Steam Generator Tube Plugging Criteria for ODSCC at Tube Support Plates", Westinghouse Electric Corporation, Proprietary Class 2, March 1992.

8.5 WCAP-14123 (SG-94-07-009), "Beaver Valley Unit 1 Steam Generator Tube Plugging Criteria for Indications at Tube Support Plates July 1994".

8.6 SG-94-05-023, "Cook-1 Cycle 13 IPC Assessment", Westinghouse Nuclear Services Division, June 9, 1994.

8-1

THE END Discard this sheet.

That's all there is.

8-2

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