summary (css) f ramatome · designed model 51 sgs with 7/8-inch od mill annealed alloy 600 tubing...

20697-3 (12/95)

F RAMATOMETCCHHDLOGIES

CALCULATIONSUMMARYSHEET (CSS)

Document Identifier 86 - 5003756 - 00

Title Diablo Canyon Unit 1 - 1R9 Voltage-Based Repair Criteria 90 Day

PREPARED BY: REVIEWED BY:

C. G. THURSTON A. M. BROWN

SIGNATURE SIGNATURE

TITLE ENG, iV DATE + ~ TITLE SR. SER. ENG. DATE

COSTCENTER 12742

REF.PAGE(S) 64

TM STATEMENT:REVIEWER INDEPENDENCE

PURPOSE AND SUMMARYOF RESULTS: i

This report provides the results of the Diablo Canyon Unit 1 February 1999 Outage (1R9) with respect to (1) theeddy current inspection of the steam generator tubes at TSP intersections and (2) the implementation of theAlternate Repair Criteria as specified in Generic Letter 95-05 for ODSCC at TSP intersections in Westinghouse-designed steam generators with drilled supports and alloy 600 tubing. This summary also provides the projectedEOC-10 probability of burst and leak rate tube integrity calculations as required for ARC implementation. The

allurgical examinations for the pulled intersections from SG 1-2 were performed by others and consequently areessed in a separate report.

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Table ofContents

ection Page

1.0Glossary .

Introduction .

...... 4

...... 5

2.0 Execution Summary

3.0 Background.

4.0 DCPP-1R9 1999 Pulled Tube Locations .10

5.0 DCPP-1 EOC-9 Inspection Results and Voltage Growth Rates..5.1 Inspections for Inservice Tubes5.2 Inspection Results (Inservice Tubes for Cycle 9).5.3 Plus Point Confirmation Results (Inservice Tubes for Cycle 9) ......5.4 Inspection Results (Deplugged Tubes).5.5 Inspection Results Summary.5.6 Voltage Data Review and Voltage Growth..5.7 Upper Voltage Repair Limit5.8 Bobbin Coil Probe Wear ~

12

12

13

....1415

15

17

... 18

....19

Bobbin Voltage Distributions....6.1 EOC-9 (As-found) Voltage Distributions.6.2 Repaired Indications6.3 DOS Indications Left in Service .

6.4 BOC-10 Voltage Distribution ....................,..

2929

....292930

6.5 Cycle Operating Period..............................~........... ~ ~.... ~ . ~ .~.... ~ ~.......... 306.6 Voltage Growth Distributions....6.7 NDE Uncertainty Distributions.6.8 Projected EOC-10 Voltage Distributions..

303233

7.0 Database Applied for Leak and Burst Correlations.7.1 Conditional Probability ofBurst7.2 Conditional Leak Rate ..

...58....58

.59

8.0 Tube Integrity Methods and Evaluations .

8.1 Leak Rate and Tube Burst Probability for EOC-10.8.2 Summary and Conclusions.

... .... 6 1

........ 62

9.0 References ........ ~ ~ . ~ ~ ~ ~ ~ ~ ~ ~ ~ 64


Term DefinitionGlossary ofAcronyms

ARCBOCCPDFCFRCLTDCPPDISDOSDNFEFPDEFPYECTEOCFSFTIGLGPMISIMSLBNDENDDNRCODSCCPG&EPOBPODPOLPWSCCRPCRTSSGSERTSTSPWEXTEX+Point

Alternate Repair CriteriaBeginning of CycleCumulative Probability Distribution FunctionCode of Federal RegulationsCold-Leg ThinningDiablo Canyon Power PlantDistorted ID Support Signal with possible IndicationDistorted OD Support Signal with possible IndicationDefect Not FoundEffective Full Power DayEffective Full Power YearEddy Current TestEnd of CycleFree SpanFramatome Technologies, Inc.NRC Generic Letter 95-05Gallons per MinuteIn-service InspectionMain Steam Line BreakNon Destructive ExaminationNo Detected DefectNuclear Regulatory CommissionOutside Diameter Stress Corrosion CrackingPacific Gas and Electric CompanyProbability of BurstProbability of DetectionProbability of LeakPrimary Water Stress Corrosion CrackingRotating Pancake CoilReturn to ServiceSteam GeneratorSafety Evaluation ReportTechnical SpecificationTube Support PlateWestinghouse Explosive Tubesheet ExpansionPlus Point Coil


Introduction

The Diablo Canyon Power Plant (DCPP) Unit 1 completed the ninth cycle of operation andsubsequent steam generator ISI in February of 1999. The unit employs four Westinghouse-designed Model 51 SGs with 7/8-inch OD mill annealed alloy 600 tubing and '/4-inch carbonsteel drilled-hole tube support plates.

Axial ODSCC has been confirmed within the TSP regions of the steam generators and is a

current degradation mechanism at both DCPP units. The NRC Generic Letter 95-05, Ref. 1,

outlines an alternate repair criteria (ARC) for allowing tubes containing ODSCC indications toremain in service if the indications are totally contained within the TSP and the measuredbobbin voltage is <2.0 volts. The complete list of exclusion criteria is provided in section 1.b ofRef. 1. The NRC has approved implementation of the voltage-based repair criteria at bothDCPP units per Ref. 2. It should be noted that this ninth refueling outage (1R9) is the firstimplementation of the voltage-based repair criteria at Unit 1 and the second overall at DCPP.The eighth refueling outage at Unit 2 (2RS) was the first implementation of the ARC at DCPP.

In accordance with the Generic Letter 95-05, ARC implementation requires a pre-startupassessment (Ref. 3) and a 90 day post-startup tube integrity assessment. The reports are specificto support-plate ODSCC and are similar to probabilistic condition monitoring and operationalassessments, respectively. Each assessment must include calculated conditional probability ofburst and calculated leak rate during a postulated MSLB with the 90 day report providing amore detailed account of the inspection relative to the ARC and addressing the projected growthofdegradation over the next operating cycle.

Framatome Technologies, Inc. (FTI) uses Monte Carlo codes, as described in Refs. 4 and 5, toprovide the burst and leak rate analysis simulations. These codes are based on the methods inRef. 6. The inputs for this analysis include the BOC (as-found) bobbin voltage distributionsadjusted with the NRC-approved probability of detection, repaired tubes, tubes returned toservice, measurement uncertainties, and industry-bounding voltage growth rate distributions.The analysis outputs project EOC bobbin voltage distributions and the resulting probability ofburst and leak rate. The correlation parameters used in the simulation are taken from the EPRIODSCC ARC Updated Database (Ref. 7) as reviewed in Section 7 of this report. This referencecontains the latest updated correlations of bobbin voltage to burst pressure, leak rate, andprobability of leakage.

This ARC 90-Day Report provides a detailed summary of the bobbin and RPC (+Point) probeinspection results as well as the probabilistic burst and leak results for the projected EOC-10voltage distributions. As prescribed in Section 6.b of Generic Letter 95-05, this 90-Day Reportprovides, at a minimum, the following information:

~ Review of 4 pulled tube intersections removed from SG 1-2 during 1R9 (Section 4.0) insupport of the ARC, and the associated field NDE results. The destructive examinationresults are addressed in a separate report.

~ EOC-9 voltage distributions ofall indications found during 1R9 (Tables 6-1 through 6-4 andFigures 6-1 through 6-4).


~ Cycle 9 voltage growth rate distributions .with comparisons to the industry average rate(Tables 6-5 and 6-6 and Figures 6-13 through 6-16).

~ Cycle 10 voltage combined active and deplugged tube growth rate distributions (Tables 6-9

through 6-12 and Figures 6-17 and 6-18).~ EOC-9 voltage distribution of repaired indications (Tables 6-1 through 6-4 and Figures 6-5

and 6-6).~ Voltage distribution for indications left in service at BOC-10 confirmed or not inspected by

Plus Point (Tables 6-1 through 6-4 and Figures 6-9 and 6-10).~ Voltage distribution for all DOS indications left in service at BOC-10 (Tables 6-1 through

6-4 and Figures 6-11 and 6-12).~ NDE examination uncertainty distribution used in predicting the EOC-10 voltage

distribution (Table 6-7 and Figure 6-19).~ Projected EOC-10 voltage distributions (Table 6-8 and Figures 6-20 through 6-23).~ Results of tube integrity calculations for probability of burst and leak rate at MLSB

conditions at the EOC-10 including the correlations that were used (Sections 7 and 8).

The 1R9 scope of eddy current inspections at DCPP Unit 1 included a 100% full-length bobbincoil inspection of all four steam generators. A detailed description of the inspection scope andresults is provided in Section 5 of this report. The NDE results for pulled tube intersections arereviewed in Section 4, and Section 6 reviews the bobbin voltage distributions and associatedgrowth distributions. Sections 7 and 8 include a discussion of the correlations used (Ref. 7) andthe tube integrity assessments and calculations to confirm that steam generator tubing willretainadequate margin to structural and leakage integrity through to the next scheduled outage.

As noted earlier, ARC implementation also requires completion of preliminary burst and leakrate analyses as a basis to justify plant restart. For DCPP Unit 1, this analysis (Ref. 3) wassimilar to a condition monitoring assessment and used actual "as-found" EOC-9 bobbinvoltages, adjusted for NDE uncertainty. This "alternative" tube integrity calculation is allowedper section 2.c of Generic Letter 95-05. The analyses concluded that the as-found probability ofburst and conditional leak rates for EOC-9 were well within allowable limits.


Executive Summary

A total of 216 bobbin coil distorted outside diameter (OD) support signal (DOS) indicationswere detected at TSP intersections during the Unit 1R9 ISI that were candidates for the ARC.131 DOS indications were inspected with Plus Point and 113 of those confirmed as axiallyoriented ODSCC. About 39 percent (85 DOS indications) were not required to be inspectedwith Plus Point. Of the 216 indications, 18 were greater than 1.0 volt by bobbin coil, and onlyone indication (at 2.26 volts) was detected that was greater than the 2.0 volt lower repair limit.There were no indications detected that exceeded the upper repair limitof 4.9 volts (Ref. 9). 12

of the confirmed ODSCC indications required repair and one was pulled in support of the ARCresulting in 13 tubes being removed from service.

Of the 216 bobbin DOS indications, 52 were returned to service by the deplugging of 35 tubesoriginally plugged during 1R8 due to ODSCC at TSPs. All ofprevious flawed intersections re-confirmed as ODSCC, and several new ODSCC indications were found as discussed in Section5.4.

The overall 1R9 average bobbin voltage including deplugged tubes was found to be 0.56 volts,and the voltage range extended from a low of 0.06 to a high of 2.26 volts. The 1R9 averagevoltage for inservice tubes was found to be 0.51 volts, slightly higher than that found during the1R8 and 2R8 outages, which was about 0.45 volts. The voltage range for deplugged tubesextended from a low of0.21 to a high of 1.77 volts.

The average growth rate for Unit 1 Cycle 9 was 0.102 volts or 29.6% per EFPY for tubesinservice during the cycle. This growth rate is very near the 30% per EFPY criteria specified inthe Generic Letter 95-05. In addition, the measured growth rates calculated for Cycle 9 wereabout twice that of Cycle 8 of Unit 2 (which was 13.3% per EFPY, Ref. 14). No comparisonsfor growth can be made to previous Unit 1 cycles at this time because 1R9 is the firstimplementation of the voltage-based criteria at Unit 1. The reasons for the substantially largergrowth rate for Unit 1 in comparison to Unit 2 are not understood at this time. No significantdifferences in design, operation, or material construction exist between the units.

The BOC-10 voltage distributions for input into the Monte Carlo simulations were determinedby applying the NRC-mandated probability of detection (POD) of 0.6 to the as found DOSpopulation, subtracting the repaired tube indications, and then adding the deplugged tubeindications for each steam generator. Since tubes were deplugged in U1R9, the growthdistributions to be used for Cycle 10 growth consist of two components, i.e., active anddeplugged tube growth, which are combined per Ref. 7.

Since less than 200 indications were. found in active tubes for Cycle 9, a conservative industry-bounding growth was required to be used for the growth contribution of the active tubes to theprojected EOC10 distribution. For deplugged tubes, an EPRI-recommended limiting growth ratedistribution per Table 8-5 of Ref. 7 was used for second component contribution to theprojected EOC10 distribution. Per Ref. 7, this very conservative growth distribution issuggested for the first cycle of operation for deplugged tubes. Also no growth rate has been


established for deplugged tubes at DCPP since Unit 1 Cycle 10 will be the first cycle ofoperation with deplugged tubes containing support plate ODSCG.

These two growth rates were combined per the Ref. 7 formulations to calculate the projectedCycle 10 growth rate distribution for'nput into the Monte Carlo simulation. The mostconservative of a generator-specific or averaged overall composite growth was used along withthe respective BOC voltage distribution for each generator for each analysis.

The probability of burst and leak rate input parameters were based on the updated 1998 ARCdatabase. Conditional MSLB leak rate and tube burst probabilities were calculated for theprojected population of indications at the end of Cycle 10 using 1 million simulations. Allofthe calculated results meet the NRC probability of burst limitof lx10-2, and the DCPP Unit 1-

specific primary-to-secondary leak rate limit of 12.8 gpm (Ref. 9). SG 1-2 had the limitingresults for EOC-10, i.e,, a probability ofburst of3.09 x 10 4. SG 1-3 had the limiting EOC-10projected leak rate of 0.28 gpm (at room temperature). Both results are well within theallowable limits.

3.0 Background

ODSCC at tube-to-TSP intersections is a current damage mechanism at DCPP Units 1 and 2based on Ref. 8. Axial and circumferential PWSCC due to tube denting at tube-to-TSPintersections is also a current damage mechanism. Tube denting causes stresses on the OD andID of the tube wall where cracking can develop. Since IR6, 100% of SG tubes have beeninspected with bobbin probes each refueling cycle and a continuously augmented inspectionprogram has been implemented to inspect dented intersections with RPC. The basic RPC dentinspection methodology requires, on a SG basis, 100% of dents up to the highest supportintersection where PWSCC had previously been detected, plus 20% at the next highest TSPelevation.. In some instances, PWSCC has occurred in conjunction with ODSCC at anintersection. The associated OD indication is applicable for inclusion in the ARC calculations.

In 1R7 and 1R8, all OD distorted support plate indications were also inspected with Plus Pointsince the ARC had not been approved for implementation at DCPP. Consequently, during thoseoutages, each indication that confirmed by Plus Point was plugged. Only the DOS indications,previously referred to as OD-DSSs, that did not confirm were left in service. During 1R8, theeddy current data was acquired and analyzed in accordance with the requirements of Ref. 1.

With the approval of the voltage-based repair criteria for 1R9, DOS indications less than 2 voltsat non-dented intersections were generally not required to be inspected with Plus Point unless aninspection was performed as associated with another degradation mechanism (Ref. 8).

Based on Ref. 8, approximately 35 tubes previously plugged for axial ODSCC at TSPs wereidentified as candidates for plug removal and return to service during 189. This was the firsteffort by DCPP to return previously plugged ODSCC tubes to service.

The majority of the Plus Point confirmed ODSCC are located at the 01H and 02H intersections,and most are located at dented TSPs. 45 tubes with confirmed ODSCC at TSPs were pluggedduring 1R8. Since the 1R8 outage inspections were carried out in accordance with Generic


Letter 95-05 requirements in regard to bobbin probe wear monitoring and voltage normalizationofcalibration standards, assessments ofprobe wear can be accomplished for the effectiveness ofthe 15% tolerance criteria for wear and the adequacy of the 75% voltage criteria for re-inspection. That review is conducted in Section 5.S.

i


4.0 DCPP-1R9 1999 Tube Pull Locations~

~

During 1R9, four intersections from tubes R16C57 and R37C32 were removed from the hot-legside of SG 1-2. R16C57 was cut just below 2H removing one intersection, and R37C32 was cutjust below 4H removing three intersections. R37C32 at 3H had a DOS call that confirmed as

axial ODSCC by Plus Point. R37C32 at 1H and 2H were both NDD by bobbin and Plus Point.R37C32 at 3H had a DOS call that confirmed as axial ODSCC by Plus Point. R16C57 at 1Hhad a DNT and a DIS indication by bobbin and contained axial PWSCC as confirmed by PlusPoint.

The NRC Generic Letter 95-05 requires that four intersections be removed with two of theintersections having Plus Point-confirmed ODSCC. The three intersections pulled in R37C32meet the selection criteria listed in section 4.b of Generic Letter 95-05. The 1H intersectionpulled from R16C57 was pulled to perform a special axial load test on dented TSPs in supportof a future ARC effort for dispositioning support plate PWSCC. In a phone call with PG&E,the NRC agreed to credit this tube pull for the Generic Letter 95-05 ARC in lieu of pullinganother intersection containing axial ODSCC.

The in-generator production and post-production NDE results for the four intersections aresummarized in Table 4-1. The required destructive examinations in support of alternate repaircriteria per section 4.c of the Generic Letter 95-05 are addressed in a separate report.

FTI Non-Proprietary 10 86-5003756-00

Table 4-1Review ofNDE Indications From

Inspections on SG 1-2 Pulled Tube Intersections from R16C57 and R37C32

Tube/LocationR37C32/01H TSP

Field In-SG ECTBobbin: NDD+Point'DD

R37C32/02H TSP

R37C32/03H TSP

Bobbin: NDD+Point NDD

Bobbin: 0.74V, 101, DOS+Point: 0.76 V, 106', SAI

R16C57/01H TSP Bobbin: 5.14 V, 178', DNTBobbin: 1.38 V,31', DIS+Point: 0.53 V,6', SAI

Le end ofAbbreviations:NDD = no detectable degradation SAI ~ single axial indicationDIS = distorted ID support plate signal DNT ~ dent signal

DOS ~ distorted OD support plate signal


.0 DCPP-1 EOC-9 Inspection Results and Voltage Growth Rates

Since tubes were deplugged during 1R9, this section addresses deplugged and active tubesseparately and then gives an overall summary of the inspection in Section 5.5.

5.1 Inspections for Inserv ice Tubes

The 1R9 bobbin coil inspection consisted of a 100% full-length bobbin coil examinationof tubes in all four steam generators except for the U-bends of rows 1 and 2, which wereinspected with a single coil +Point probe. A 0.720 inch diameter bobbin probe was usedfor the full-length examinations including all TSP intersections in the hot and cold legs.Probe designs used included those with changeable centering feet, which requiredsignal-to-noise tracking per Refs. 8 and 11.

During 1R9, RPC (+Point) examination of TSP intersections was conducted as followsin the support of the voltage-based ARC.

~ 100% ofDOSs greater than 2 volts.

~ 100% ofDOSs at dented intersections.

~ 100% ofDOSs in the defined CLT region.

~ 100% of ID distorted support signals (DIS).

~ 100% of TSP intersections containing mix residual signals exceeding a voltagethreshold that could mask a 1.0 volt bobbin DOS signal, intersections with suspectedTSP ligament cracking, intersections with DOSs in the wedge regions, or indicationsthat may extend outside the TSP crevice.

~ 100% of dented intersections up to the highest TSP elevation where PWSCC hasbeen previously detected in that specific steam generator, plus 20% of dents at thenext highest TSP elevation. For 1R9, this translated into the following inspections:

1. SG 1-1 and SG 1-4: 100% from 1H to 3H, and 20% at4H.2. SG 1-2: 100% from 1H to 6H, plus 20% at 7H.3. SG 1-3: 20% at 1H.4. In addition, where 100% inspections are not required, inspect at least 20% of the

greater than or equal to 5 volt dents up to 7H in any steam generator (and atleast 50 > 5 volt dents or 100% ifthere are less than 50).

(Note: The above DCPP Unit 1 greater than 5 volt dent inspection strategy has beenapproved by the NRC (Ref. 2) in lieu of having to inspect 100% of greater than 5 voltdents as required by Ref. 1.)


5.2 Inspection Results (Inservice tubes for Cycle 9)

The results of the inspections with respect to the ARC were as follows:

(1) A total of 179 intersections with distorted OD-type support plate signals (DOSs)were identified in all four steam generators for the tubes that were inservice duringCycle 9. 158 of the DOSs were located in the hot leg and 21 were located in thecold leg.

(2) Three DOS indications that were confirmed by Plus Point as ODSCC also had axialID (PWSCC) flaws at the same intersection. These tubes, one in SG 1-1 and two inSG 1-2, were removed from service but the OD component of the OD/ID flaws wasconsidered applicable for inclusion in the ARC calculations.

(3) Of the 21 cold-leg DOS indications, 19 were located in the cold-leg thinning (CLT)regions (i.e., at the periphery and at 1C or 2C). These 19 indications are consideredattributable to different degradation mechanism and were not included in the DOSanalysis pool for the 1R9 ARC calculation. Four of the 19 cold-leg DOS indicationswere confirmed as OD-initiated volumetric indications. These tubes, two in SG 1-1,one in SG 1-3, and one in SG 1-4, were removed from service by plugging. Theoverall breakdown for CLT DOS indications was: 9 in SG 1-1, 4 in SG 1-2, 5 in SG1-3, and one in SG 1-4. The remaining two, both located in SG 1-3 at 5C, wereincluded in the ARC DOS population.

(4) The term AONDB (axial ODSCC not detected by bobbin) was assigned to 5 hot-legRPC indications. These indications were determined to be axial ODSCC at dentedintersections by Plus Point but had no associated DOS call by bobbin. Each of thefive intersections had DNT calls made with associated OD phase angles. Dentingmasks the signal voltages for these indications such that the DOS bobbin voltagesare unobtainable. There were actually no DOS calls made for these indications. Thebobbin voltages used were calculated (see discussion below) and then included inthe pool ofDOSs used in the Monte Carlo simulation.

(Note: A bobbin voltage was calculated and assigned to each AONDB flaw basedon the associated Plus Point voltage using a correction factor as shown in Figure 5-1. The total 1R9 population of axial ODSCC calls (with DOS voltages) was used todevelop a simple linear regression (straight-line approximation). The meanapproximation, i.e., averaged linear fit to data (solid line in figure), was consideredto be reasonably accurate for this correlation. The slope and intercept for the meanfit was 0.705 and 0.403, respectively, and the R squared value for the mean was0.16.)

These five tubes were removed from service per Ref. 9. One of these indicationswas located SG1-1 and four were located in SG 1-2. However, since these AONDB


r

indications are considered to be DOSs and're to be included in the ARCcalculations, the total number of DOS indications found is considered to be 183 inactive tubes.

An upper voltage repair limit (URL) must be calculated prior to the eddy currentinspection. This is the voltage value, above which, DOS indications no longer qualifyfor the ARC. No indications were found approaching the URL, which was determinedto be 4.9 Volts. This calculation is further reviewed in Section 5.7 of this report. Thelower repair limitof 2.0 volts is based on Ref. 1 and this voltage was exceeded by oneindication (at 2.26 volts in SG 1-1). The bobbin and associated Plus Point results forthis indication are shown in the table below.

Row2323

Col4646

Ind Elev Inch1

DOS 1H 0SAI 1H -0.02

Volts2.261.67

Deg4584

Probe720MU720+P

After exclusion of the CLT indications, the total number ofactive DOSs to be analyzeddropped from 183 to 164 indications. The overall breakdown of the DOS analysis poolthen became: 38 in SG 1-1,72 in SG 1-2,43 in SG 1-3, and 11 in SG 1-4. The voltagerange extended from a low of 0.06 to a high of 2.26 volts. For information, all of theDOS voltages found above 0.8 volts are shown in Table 5-4. Also, Tables 6-4 through6-7 contain the as-found voltage distribution of DOSs identified during the bobbin coilinspection for each steam generator. Note that these tables also show deplugged tubeindications.

5.3 Plus Point Confirmation Results (Inservice tubes for Cycle 9)

Of the 164 DOS indications, 79 (15 in SG 1-1, 48 in SG-12, 12 in SG-13, and 4 in SG-14) were inspected with Plus Point. The vast majority of these inspections were requiredbecause of denting in the same intersection. 68 of these indications were confirmed as

axial ODSCC, resulting in a confirmation rate of 86% for those inspected. 56 of theconfirmed calls were located at dented intersections. The breakdown for ODSCCindications at dented intersections included: 13 in SG 1-1, 46 in SG 1-2, 5 in SG 1-3,and 4 in SG 1-4.

Of the 68 confirmed axial ODSCC indications, 13 were removed from service forreasons'explained in Section 5.5. The DCPP acceptance criteria for confirmed axial


ODSCC, based on Ref. 9, includes: (a) DOS voltage less than or equal to 2 volts, (b)dent voltage less than 5 volts, (c) no associated PWSCC, (d) location within bounds ofthe TSP, (e) no circumferential extents, (f) no TSP ligament gaps, (g) no AONDB, and

(h) the defect should not be located in a currently-defined wedge intersection. Plus Pointconfirmed ODSCC indications not meeting the acceptance criteria were plugged.

A total of 55 confirmed axial ODSCC indications, in 53 tubes, were saved fromplugging by use of the ARC. The distribution was 9 tubes in SG 1-1, 37 tubes in SG 1-2,3 tubes in SG 1-3, and 4 tubes in SG 1-4. Ifthe tubes not inspected by Plus Point areconsidered and the confirmation rates are applied at 50% conservatively, approximately12 tubes in SG l-l, 12 tubes in SG 1-2, 16 tubes in SG 1-3, and 4 tubes in SG 1-4 wereadditionally saved by ARC implementation, a total of 44 more tubes. The projectedgrand total would then be about 97 tubes saved by ARC implementation.

5.4 Inspection Results (Deplugged tubes during 1R9 for Cycle 10)

During 1R9, 35 previously plugged tubes in 1R8 were deplugged, re-inspected, andreturned to service. From this group of recovered tubes, 52 DOS calls were made, 21 inSG l-l, 13 in SG 1-2, 16 in SG 1-3, and 2 in SG 1-4. The deplugged tubes wereinspected with bobbin and Plus Point per Ref. 8. All of the DOS indications wereinspected with Plus Point. 45 of the 52 DOSs confirmed as axial ODSCC but none ofthe deplugged tubes required replugging based on the Ref. 9 acceptance criteria.

All of the previous ODSCC intersections re-confirmed as ODSCC by Plus Point. Inaddition, new DOS indications were found in several tubes that were not observed in1R8, and several of the new DOSs confirmed as ODSCC. There were 15 new DOSs ofwhich 8 confirmed as axial ODSCC indications. Each had relatively low bobbin signals,and none were dented. In SG 1-1, there were 4 new DOSs and each one confirmed asODSCC. In SG 1-2, there were 2 new DOSs and both confirmed as ODSCC. In SG 1-

3, there were 9 new DOSs with 2 confirming as ODSCC, and in SG 1-4, there were nonew DOS calls made.

The average voltage of DOSs in the deplugged tubes was found to be 0.71 volts,compared to an average of 0.51 volts for the tubes previously inservice for Cycle 9. Thevoltage range extended from a low of 0.21 to a high of 1.77 volts (again in SG 1-1).

5.5 Inspection Results Summary

The following provides an overall summary of the 1R9 inspection results for thecombined set of active plus deplugged tubes:

~ 230 DOSs were identified. 19 were removed from the ARC population because theywere located in CLT regions and 5 AONDB indications were added as DOSs. This


resulted in a total of216 DOS indications for inclusion in the ARC calculations. Theoverall breakdown was as follows: 59 in SG 1-1, 85 in SG 1-2, 59 in SG 1-3, and 13

in SG 1-4.

~ O'e DOS indication exceeded the 2.0 volt repair limit, only 18 of the indicationsexceeded 1 volt, and 10 of those 18 indications were located in deplugged tubes (seeTable 5-3). The average DOS voltage was found to be 0.51 for inservice tubes and0.71 for deplugged tubes.

~ Of the 216 DOS indications, 113 were confirmed by +Point as axial ODSCC, 18

were DNF, and 85 were not inspected.

~ 13 confirmed axial ODSCC indications were removed from service during 1R9: 3

were repaired due to PWSCC being detected at the same intersection (ID/OD flaw),3 were repaired because ODSCC confirmed in a wedge intersection, and 5 wererepaired because of AONDB. In addition, 1 was repaired for tube pull, and 1 wasrepaired because the bobbin voltage exceeded the lower voltage repair limit andconfirmed axial ODSCC.

~ The number of Cycle 9 DOS indications as well as the maximum and averagevoltages as a function of support plate location are summarized in Tables 5-1 and 5-

2, respectively, for the active and deplugged tubes. The data, as in previous reviews,show a strong pre-disposition of ODSCC to occur in the first and second hot-legTSPs (165 out of the 216 indications occurred at 1H or 2H intersections), althoughthe mechanism extended to higher TSPs. This distribution indicates thepredominant temperature dependence of ODSCC, similar to that observed at otherModel 51 plants. Also, based upon the low number of indications and their lowvoltage amplitude responses, ODSCC at the TSPs in DCPP Unit 1 is still notconsidered to be a very active damage mechanism.

~ There were no circumferential ODSCC indications at the TSPs. However, therewere 3 circumferential PWSCC indications (all located in SG 1-2) at dented TSPsresulting in those 3 tubes being plugged.

~ 58 hot-leg ID distorted supported signal (DIS) indications were called with bobbin.7 confirmed as axial PWSCC. DIS indications are not candidates for the ARC. Thebreakdown for these indications was: 10 in SG 1-1, 21 in SG 1-2, 6 in SG 1-3, and21 in SG 1-4.

~ Based on the number of repair indications, a total of 203 ARC-applicable DOSindications willbe inservice for Cycle 10 operation.


5.6 Voltage Data Review and Voltage Growth

The maximum and average DOS voltages per support plate location for each SG duringCycle 9 are summarized in Tables 5-1 and 5-2 for active and deplugged tubes,respectively. The average voltage found for active tubes was 0.47, 0.43, 0.66, and 0.57respectively, for SG 1-1, SG 1-2, SG 1-3, and SG 1-4 with the composite average being0.51 volts. For deplugged tubes, the average voltage was found to be 0.61, 0.70, 0.82,and 0.91 respectively, with the composite average being 0.71 volts.

Of the 159 DOS calls made at 1R9 for tubes in service during Unit 1 Cycle 9, only 15

were called in 1R8, the prior outage, and were not plugged. Therefore, voltage "lookups" were performed of the 1R8 data to assess voltage growth in support of the ARC.No adjustments to the 1R8 data were needed since the data analysis and acquisitiontechniques used were in accordance with the requirements of Generic Letter 95-05. Ofthe 1R8 look ups performed, none were found to be NDD in 1R8 (except for theAONDB indications) although 10 of them were at voltages below 0.1 volts (down to0.02 volts). As indicated previously, the requirements for probe wear were alsoimplemented during 1R8. Considering the exclusion of the five AONBD indications,211 indications were included in the growth distribution, i.e., 159 for active tubes and52 for deplugged tubes. In accordance with the requirements of Generic Letter 95-05,voltage growth rates were only evaluated for those intersections at which bobbinindications could be identified at both the 1R8 and 1R9 inspections. For this reason, thenumber of indications used in the determination of the average growth rate is five lessthan the total number of indications detected.

Due to the uncertainties in the eddy current process, some of the growth comparisonsare expected to result in decreases in voltage (i.e., negative growth). Per Generic Letter95-05, it is appropriate to consider these negative growth rates as part of the averagegrowth rate. The use of the negative growth rates applies only when determining the

upper voltage repair limit.

Active tubes only are used to develop a growth distribution for Cycle 9. For theprojected Cycle 10, the active and deplugged indications are combined using theformulation reviewed in Section 6.6.

Table 5-3 provides average Cycle 9 growth rates per steam generator for the 159 DOSindications in active tubes. Each of the four SGs showed an overall positive average-cycle growth rates ranging from about 0.12 to 0.24 volts per cycle. The compositeaverage rate for DCPP Unit .1 during Cycle 9 was 0.187 volts, which is equivalent to0.102 volts per EFPY (based on 1.62 EFPY for Cycle 9). Note that the compositeaverage EOC-9 voltage was 0.34, resulting in an average Cycle 9 growth rate of 29.6%per EFPY.

Table 5-3 also provides the average Cycle 9 growth rates per SG for indications indeplugged tubes. The growth rate for deplugged tubes was found to be about 55% per


EFPY. These overall and generator-specific growth rates are for information only sincethe tubes were plugged.

In both cases (active and deplugged tubes), these Cycle 9 growth rates are not applied tothe Cycle 10 projections. Rather, bounding industry growth rates are used for the MonteCarlo simulation as explained in Section 6.6.

Recently, some plants with '/4" tube SGs experienced growth rates that seem to increasewith the beginning of cycle (BOC) voltage. To determine ifDCPP Unit-1 exhibited a

similar trend, growth rate data for Cycle 9 was plotted against BOC voltage, and theresulting plot is shown in Figure 5-2. It is evident from this figure that Cycle 9 growthdata do not show any trend to increase with BOC voltage. The trend, if any, is forgrowth to decrease with increasing BOC voltage.

Tables 5-4 and 5-5 provide a review of the largest voltages and the largest voltagegrowth intersections, respectively, identified during 1R9.

5.7 Upper Voltage Repair Limit

Per Generic Letter 95-05, the upper repair limitmust be calculated prior to each outage,and the more conservative of the plant-specific average growth rate per EFPY or 30percent per EFPY should be used in the determination as the anticipated growth rateinput for this calculation. The upper voltage repair limitwas calculated prior to the 1R9inspection and was determined to be 4.9 volts (Ref. 9). This calculation is based on thefollowing formula:

Vvm,—Vsr,

% VKDB % VCG1+ +

100 100

where: VUR1. = upper voltage repair limit,VNDE = NDE voltage measurement uncertainty 20%,VCG = voltage growth anticipated between inspections = 30%,VSL = voltage structural limitfrom the burst pressure —bobbin voltage correlation, where the

limitof 8.3 volts was used based on Ref. 12.

Although the upper repair limitwillnot be calculated again until shortly before the nextinspection, the average growth rates from Cycle 9 are documented in this report toverify that the 30% per EFPY remains bounding for DCPP Unit 1. As shown in Table 5-

3, the average percent growth for active tubes for Cycle 9 at 29.6% per EFPY is verynear the NRC minimum. Regardless, the 30% per EFPY growth rate should still beused to calculate the upper repair limitfor the next DCPP Unit 1 inspection.


5S

5.8.1

Bobbin Coil Probe Wear

Implementation of the Wear Criteria

The p'robe wear criteria approved by the NRC (Ref. 12) was applied during the EOC-9inspection. This reference provides the guidelines to be used for bobbin probe wearassociated with voltage-based repair implementation. When a probe does not pass the15% wear limit, this criteria requires that only tubes with indications above 75% of therepair limit inspected since the last successful probe wear check be re-inspected with a

good probe. Since the repair limit for DCPP Unit 1 is 2.0 volts, all tubes containingindications above 1.5 volts that were originally inspected with a worn probe wererequired to be re-inspected with a new probe. A summary of probe wear monitoring atDCPP Unit 1 during 1R9 was reviewed in Ref. 10.

During the 1R9 inspections, 2 DOS indications in excess of 1.5 volts were inspectedwith a probe that failed the wear check. Both of these "RSS" indications were located inSG 1-1. The 2 tubes that contained these indications were re-inspected per therequirements, and the results are shown in Table 5-6. The re-inspection resulted involtage values very similar to the original voltages (within 6%). No other indicationswere detected during the re-inspection. This provides confirmation that otherindications of lesser voltages that were inspected with the worn probes do not need to bere-inspected and that the 75% criterion is adequate.

The Ref. 12 probe wear criteria also require an assessment of tubes that were inspectedwith probes that failed the wear check in 1R8 but were not re-inspected because theyeither contained no indication, or the indication was below the 1.5 volt threshold for re-inspection. Specifically, an evaluation is required if "large" indications and/or a non-proportionate number of new indications are detected in tubes which were inspectedwith a probe that failed the probe check in the prior outage. This evaluation should alsoaddress whether or not a more restrictive probe wear criteria is needed. Per Ref. 12,"Large" is defined to be greater than approximately 0.5 volts. This specific requirementis not applicable to 1R9 since it was the first implementation of the ARC. However,because probe wear monitoring was voluntarily performed in 1R8, an evaluation of thisrequirement is conservatively developed for information and possible future trending.

The results of this evaluation are summarized in Table 5-7. As indicated, 144 of the159 DOS indications found during 1R9 were new, and 75 of the 144 new indicationswere inspected with a worn probe in 1R8. 59 of the new indications were > 0.5 voltsand of those 32 were inspected with a worn probe in 1R8. These results show that'theoverall number of new indications inspected with a probe that failed the wear check(i.e., 144 total compared to 75 with worn probes for all indications and 59 totalcompared to 32 with worn probes for indications above 0.5 volts) are reasonablyproportionate (about 50% ratio in both cases). The ratio would be reduced if oneaccounts for the 36 DOS indications plugged in 1R8 that would otherwise have been leftin service ifthe ARC was licensed at that time. Probe wear is not considered to be thereason for the large number ofnew DOS indications detected during IR9.


SG 1-2 had relatively high percentage (65%) of new indications that were inspectedwith a worn probe in 1R8, but it is not considered to be non-proportionate since nearly70% of them were less than or equal to 0.5 volts. Probe wear also is not considered tobe the reason for the relative higher percentage of new DOS detected in this generatorfrom probes that failed the wear check in 1R8.

The largest new DOS indication in tube inspected with a worn probe in 1R8 was the2.26 volt indication in SG 1-1 that exceeded the lower voltage repair limit. However, itshould be noted that this tube was extremely pilgered and the flaw was evident in thelook-up of this indication for growth. Therefore, probe wear is not considered to be thereason for this DOS indication not being called in 1R8. This tube was not selected fortube pull because ofnoisiness of the data.

In conclusion, the NRC requirements regarding probe wear monitoring during an ARCbobbin coil inspection listed in Ref. 9 were complied with during the 1R9 eddy currentexamination at DCPP Unit 1. The current 75% probe wear criteria is consideredadequate, and a more restrictive probe wear criteria is not needed.

5.8.2 Use of'Bobbin Probes with Changeable Feet Centering

The centering feet on a bobbin probe are the parts that wear most during use, and thiswear is the bases for implementing the 215% wear tolerance criteria to ensure consistentquality of the bobbin voltage signals. The Ref. 11 safety evaluation determined that theuse of the changeable foot bobbin probe meets the NRC requirements whenimplementing the voltage-based repair criteria. Consequently, this new probe was usedfor data acquisition during 1R9 in accordance with the following requirements.

When the probe failed the probe wear check, this new design allows the probe'scentering feet to be replaced in lieu of replacing the entire the probe. Replacing the feetand subsequently acquiring an acceptable new wear calibration permitted the probe tobe treated as "new" again. In addition to wear measurements, Ref. 11 required a checkof the signal-to-noise (S/N) ratio using the 40% TW ASME standard hole at eachsubsequent feet replacement. Ifthe S/N ratio is determined to change by more than 30%with respect to the original S/N ratio for that probe with the original centering feet, it isconsidered to be indicative of a potential probe electrical deficiency. At this point, theentire probe assembly was replaced. Probes with feet changeout results in the optimumnumber of probe heads being used and less radiation exposure for platform personnelsince the feet changeout takes less time than a probe changeout.


Table 5-1DCPP Unit 1 February 1999 Outage (1R9)

TSP Voltage Distribution for Active Tubes in Service during Cycle 9

Steam Generator 1-1 Steam Generator 1-2

Tube Support Number ofPlate Indications

MaximumVoltage

AverageVoltage

Tube SupportPlate

Number ofIndications

MaximumVoltage

AverageVoltage

1H

2H

3H

4H

5H

6H

7H

CL

All Inds

30

38

2.26

0.59

0.40

0.00

0.45

0.47

0.00

0.00

2.26

0.480

0.400

0.310

0.000

0.450

0.470

0.000

0.000

0.46

1H

2H

3H

4H

5H

6H

7H

CL

All Inds

37

21

10

72

0.91

0.84

0.74

0.65

0.00

0.51

0.00

0.00

0.91

0.440

0.400

0.460

0.510

0.000

0.440

0.000

0.000

0.43


Tube Supporl Number ofPlate Indications

MaximumVoltage

AverageVoltage

Tube SupportPlate


MaximumVoltage

AverageVoltage

1H

2H

3H

4H

5H

6H

CL

All Inds

18

10

43

1.27

1.15

0.90

0.79

0.86

0.00

0.00

0.32

1.27

0.700

0.750

0.630

0.490

0.670

0.000

0.000

0.300

0.66

1H

2H

4H

5H

6H

7H

CL

All Inds

1.17

0.80

0.52

0.57

0.00

0.00

0.00

0.00

1.17

0.630

0.540

0.510

0.530

0.000

0.000

0.000

0.000

0.57

Compo site of Ail Four SGs

Tube Supporl Number ofPlate Indications

MaximumVoltage

AverageVoltage

1H

2H

3H

4H

5H

6H

7H

CL

All Inds

90

37

21

2.26

1.15

0.90

0.79

0.86

0.51

0.00

0.32

2.26

0.520

0.510

0.510

0.500

0.620

0.450

0.000

0.300

0.51

Note: CL indicates a cold-leg indication at any elevation.



TSP Voltage Distribution for Deplugged Tubes Not in Service during Cycle 9



MaximumVoltage

AverageVoltage

Tube SupportPlate


MaximumVoltage

AverageVoltage

1H

2H

3H

4H

5H

6H

7H

CL

All Inds

16

21 ~

1.77

0.71

0.29

0.28

0.00

0.00

0.00

0.00

1.77

0.67

0.51

0.29

0.28

0.00

0.00

0.00

0.00

0.61

2H

3H

4H

5H

6H

7H

CL

All lnds 13

1.25

O.M

0.34

0.00

0.47

0.00

0.00

0.00

1.25

0.76

0.00

0.34

0.00

0.47

0.00

0.00

0.00

0.71

Steam Generato I'-3 Steam Generato r 1-4


1H

2H

4H

5H

6H

7H

CL

MaximumVoltage

1.52

0.86

0.60

0.45

0.94

1.76

0.39

0.80

AverageVoltage

1.23

0.69

0.60

0.38

0.94

1.05

0.39

0.66

Tube SupporlPlate

1H

2H

3H

4H

5H

6H

7H

CL

Number ofindications

MaximumVoltage

0.38

0.00

1.43

0.00

0.00

0.00

0.00

0.00

AverageVoltage

0.38

0.00

1.43

O.M

0.00

0.00

0.00

0.00

All Inds 16 1.76 0.82 All Inds 1.43 0.91

Compo site of All Fo ur SGs


MaximumVoltage

AverageVoltage

1H

2H

3H

4H

5H

6H

7H

CL

All Inds

32

52

1.77

0.86

1.43

0.45

0.94

1.76

0.39

0.80

1.77

0.76

0.60

0.67

0.34

0.71

1.05

0.39

0.66

0.71

Note: CL indicates a cold-leg indication at any elevation.


Table 5-3DCPP Unit 1 February 1999 Outage (1R9) Voltage Growth Rates

(a) Average for Active Tubes during Cycle 9

SteamGenerator

No. of IndsIncluded In

h D tBOC-9 Volts

Growth Data

Average Average PercentVoltage Growth ForGrowth Cycle 9 t1)

Average PercentGrowth Per

EFPYg)

1-21-3

Combined

376843

159

0.2810.3070.4570.3270.343

0.1830.1160.2060.2440.165

65.1%37.7%45 1%74 4%48 0%

40 2%23.3%27.8%46.0%29.6%

(b) Average for Deplugged Tubes during Cycle 9

SteamGenerator

No. of IndsIncluded In

Average

D tBOC 9 Volts

Growth Data

Average Average PercentVoltage Growth ForGrowth Cycle 9 <»

Average PercentGrowth Per

EFPY tz)

1-21-3

Combined

211316

52

0.3360.3520.4670.2150.375

0.2770.3510.3510.6900.334

82.4%99.8%75 1%

320 9%88.9%

60 9%61.6%46 4%198.1%64 9%

Notes: (1) Average percent growth for Cycle 9 is the average bobbinvoltage growth divided by the average BOC-9 voltage.

(2) Average percent growth per EFPY is based on the actualCycle 9 operating interval of 1.62 EFPY.



Summary of the Largest Voltages for Cycle 9

SUMMARYOF LARGEST VOLTAGES FOR VOLTAGE.BASED ARC REVIEWSG Count

13131314

1313

Row

2328

23

Col

4635565561

61

67

Elev

1H1H6H1H1H3H1H1H

1H

EOC

2.261.771.761.521.451.43

1.271.26

1999 Bobbin Volta esBOC

1.140.520.811.010.880.10.460.570.65

GROWTH

1.121.250.950.510.571.330.880.7

0.61

RPCConflnned7

YesYesYesYesYes

Yes

Yes

Deplugged1R9'7

YesYes

YesYesYes

Yes

RepairedTubeYes

121213

1413

1312

12131213

1213

13131313121212

13131314

10

12131415161718192021

2223242526272829

3132

37

3940

2025'l8

12

28

22204130

28

10

182925162718

875751

62

4159224363357059483471

5769717525

47

7012

1H1H1H1H1H2H1H1H2H1H1H2H1HSH

1H1H1H3H1H2HSH3H2H1H1H2H1H1H2HSC2H

1.251.241.241.181.171.151.14

0.990.980.980.970.940.930.920.910.90.880.860.860.850.850.840.84

0.830.820.820.80.8

0.470.570.750.2

0.360.520.350.580.610.280.70.36OA40.70.670.270.320.550.460.610.180.580.75OA60.640.970.250.28

0.780.670.490.980.080.150.80.680.520.640.40.370.690.240.570.480.210.230.61

0.310.390.240.660.260.090.370.18%.150.550.52

YesYes

Yes

Yes

YesYes

Yes

YesYesYes

YesYesYes

YesYes

Yes

Yes

Yes

YesYes

Yes

Yes



Summary of the Largest Voltage Growths for Cycle 9 (1997-1999)

SUMMARYOF LARGEST GROWTH RATES FOR VOLTAGE.BASED ARC REVIEW

SG

14

Count Row Col Elev

3H

1998 Bobbin Volta esGROWTH

0.1

RPCConflnned?

Yes

Deplugged1R9'?

RepairedTube

13

121312

121212

13

121313131314131313131213

12

12

13

1313

13

10

121314

15161718192021

2223242526272829

32

3738

40

2823

302023

28252922

37

1828

25

25

2032

412527

354662

61

876735415775

5932

70

5912

514840

5925

43

6963874763

1H1H1H6H1H1H1H1H1H1H1H1H1H1H1H1H3H1H

2H2H2H1H1H1H1H1H3H2H5H1H1H1H3H

2H1H1H4H

2.261.181.78

1.141.251.270.97

1.240.840.990.881.260.930.741.450.8

0.81.52

0.920.5

0.650.670.710.470.660.980.710.710.850.98

0.830.79

0.521.140.2

0.810.460.340.470.570.280.380.570.180.350.27

0.380.17

0.250.320.520.281.010.750.44

0.210.23

0.060.260.580.310.31

0.610.260.46

1.251.120.980.950.880.8

0.780.70.69

0.670.660.640.610.610.570.570.57

0.540.520.520.510.49OA80.470.440.440.420.410.40.40.40.4

0.390.370.370.370.36

Yes

YesYesYes

Yes

YesYesYesYes

YesYesYes

Yes

YesYesYes

Yes

YesYes

Yes

Yes

Yes

Yes

YesYes

Yes

Yes

Yes

IIFTI Non-Proprietary 25 86-5003756-00

Table 5-6DOS Indications that Failed the Probe Wear Check in 1R9

SG Row Col Ind Elev Inch1 Volts Deg Ext1 Probe Cal ARC Out77

28 35 RSS28 35 DOS23 46 RSS23 46 DOS

1H 0.08 1.88 851H 0.06 1.77 851H 0.09 2.23 341H 0 2.26 45

TEHTEC 720MUTEHTEC 720MUTEHTEC 720MUTECTEH 720MU

SG11CCAL00092SG11CCAL00094SG11CCAL00031SG11HCAL00084

Yes

Yes

Table 5-7Summary of Quantities ofNew ARC Qualifying Indications from

Active Tubes in Shown Categories

SG

12

13

14

Tot.

1R9DOSs(Total)

37

68

43

159

New 1R9DOSs

NDD in1RS

3765

34

144

New 1R9Ind. in

Tubes Insp'.w/ WornProbe in

1RS

19

41

15

75

New 1R9Ind. in

Tubes Insp.w/ GoodProbe in

1RS

18

2419

69

New 1R9Ind. > 0.5

Volts

2225

59

New IR9Ind.

> 0.5 Voltsin

Tubes Insp.w/ WornProbe in

1RS

13

12

32


igure 5-1: Plus Point-to-Bobbin Voltage Correlation.

DCPP-U1R9 -1999 RPC vs Bobbin Voltages

3.00

2.50

2.00

4<r

rr

rr

1.00

0.50

0.00

0t

+

04

4

4e 0 Bobbin Voltages

Linear Rt

Lower 95% Line

Upper 95% Line

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

RPC Voltage


Figure 5-2: BOC-9 Voltage Versus Cycle 9 Active Tube Growth.

1.5

1

C

0.5

OUL 0

0

4 kAyo og ~iP~~~ 0

o SG1-1

y SG1-2

g SG1-3

o SG1-4

-0.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

BOG-9 Bobbin Voltage


.0 Bobbin Voltage Distributions~

~

This section provides the voltage distributions used in the calculation of leak rate and

probability ofburst as well as calculation of the projected end-of-cycle (EOC-10) distributions.

6.1 EOC-9 (As-Found) Voltage Distributions

The voltages for the DOS indications detected during the 1R9 inspection were binned in0.1 volt increments separately for the active and deplugged tubes. The "as-found"voltage distributions used in the determination of the EOC-9 and the BOC-10distributions are shown in Tables 6-1 through 6-4 and in Figures 6-1 through 6-4.

6.2 Repaired Indications

The voltage distributions for the repaired indications are provided in Tables 6-1 through6-4 and Figures 6-5 and 6-6. A total of 13 DOS indications were removed from servicefor active tubes (3 in SG 1-1, 9 in SG 1-2, one in SG 1-3, and zero in SG 1-4). None ofthe deplugged tube indications required repair. A description of the reasons for repairwas reviewed in Section 5.5. No indications were repaired because of exceeding the

upper repair limitof4.9 volts and only one was repaired due to Plus Point confirmationofan indication greater than the lower repair limitof2.0 volts.

6.3 DOS Indications Left In Service

As required by the Generic Letter 95-05, the voltage distributions for DOS indicationswhich were returned to service for Cycle 10, regardless of Plus Point confirmation, are

shown in Tables 6-1 through 6-4 and Figures 6-11 and 6-12.

The Generic Letter 95-05 also requires that the voltage distribution of the DOSindications which were left in service that were confirmed by Plus Point to be crack-likeor were not inspected with Plus Point be provided in the 90-day report. Thesedistributions are provided in Tables 6-1 through 6-4 and Figures 6-9 and 6-10. Asdiscussed, 85 DOS indications were not inspected with" Plus Point and returned toservice, and 100 DOS indications were confirmed by Plus Point as OD-SCC andreturned to service. Therefore, this distribution excludes only the DOS indications notconfirmed by Plus Point (i.e., DNF calls).

The ODSCC confirmed DOS indications remaining in service for Cycle 10 are shown inFigures 6-7 and 6-8.


6.4 BOC-10 Voltage Distribution

To determine the BOC-10 voltage distributions, the EOC-9 as-found distributions were

adjusted to account for the probability of detection (POD), the indications that were

removed from service, and indications from deplugged tubes. In accordance with the

requirements ofGeneric Letter 95-05, a POD of 0.6 was used in the determination of the

BOC-10 voltage distributions. The number of indications in each of the EOC-9 voltagebins was divided by the POD of 0.6 to give the total number of indications assumed to

be present. This number was then reduced by the number of indications that wereremoved from service and summed with number of indications from deplugged tubes.

This relationship is shown below:

NEoceNaocto = —Nrrpalrcd + Pkcpluggcd

POD

The resulting BOC-10 distributions are shown in Tables 6-1 through 6-4 and Figures 6-1

through 6-4.

6.5 Cycle Operating Period

The operating periods used in the growth rate/EFPY calculations and voltage projectionsare as follows (Ref. 13):

Cycle 9 - BOC-9 to EOC-9 - 1.62 EFPY (actual)Cycle 10 - BOC-10 to EOC-10 - 1.5S EFPY (projected).

6.6 Voltage Growth Distributions

An analysis was performed to determine the growth rate of the DOS indications in-service for Cycle 9 (active tubes). In accordance with the requirements of GenericLetter 95-05, voltage growth rates were only evaluated for those intersections at whichbobbin indications could be identified at both the 1RS and 1R9 inspections. The actual

growth values were divided by the Cycle 9 operating interval of 1.62 EFPY to obtaingrowth values in terms of delta volts per EFPY. These normalized growth values werethen binned in 0.1 volt increments. The DCPP Unit 1 growth distributions for Cycle 9

are shown in Table 6-5 and Figures 6-13 through 6-17. For the tube integritycalculations discussed in Section 7, the negative growth values were included as zerogrowth rates as required by Generic Letter 95-05.


Per Generic Letter 95-05, a bounding probability distribution function of-growth rates

based on data from similarly designed and operated units should be used ifthe plant-specific growth rate consists of fewer than 200 indications. Since DCPP Unit 1 only has

159 indications in its Cycle 9 active tube growth rate distribution, an industry boundinggrowth rate distribution must be used. Therefore, a bounding industry growthdistribution was developed for use in the tube integrity calculations. The cumulativeprobability growth distributions for several similarly designed plants are shown inFigure 6-15. This figure also shows the DCPP Unit 1 Cycle 9 and the industry boundinggrowth distributions. Note that the DCPP Unit 1 distribution is bounded in all voltagebins by the industry bounding growth distribution. Figure 6-17 shows the DCPP Unit 1

Cycle 9 and the industry bounding growth distributions expressed as normaldistributions for comparison.

The growth distributions shown in Tables 6-5 and 6-6 and Figures 6-13 through 6-17

only address active tubes. Note that per the 1998 EPRI Database Update (Ref. 7), iftubes have been deplugged, the growth rate to be used for calculation of the projectedEOC-10 distribution should be a composite of the active and deplugged tube growths.Ref. 7 also requires that a conservative limiting growth distribution be used if thesubject cycle is the first cycle of operation for deplugged tubes to maintain the marginsin the projected burst and leak rate analyses. This is because several similarly designedplants have experienced significantly larger in-service growth rates for deplugged tubesreturned to service than tubes that were active during the prior cycle. Therefore, theactive and deplugged growth rates were calculated and combined based on Ref. 7(Equation S-1) shown below:

ni,comb = (ni,ag xNQ —: nr,ag + (ni,dg xNdp —: nt,dg

where,

riicomb = number of indications in the ith bin ofcomPosite growth distribution,n; ag

—= number of indications in the ith bin ofactive tube growth distribution,

n;d< =- number of indications in the ith bin of deplugged tube growthdistribution,

Na =- total number of indications in active tubes returned to service,

Ny> = total number of indications in deplugged tubes returned to service,

nt ag = total number of indications in the active tube growth distribution,ni dg = total number of indications in the deplugged tube growth distribution.

This correlation normalizes the active and deplugged tube growth distributions to thenumber of corresponding indications being returned to service. For the SG averagedgrowth rate, the numbers were normalized to the total number of active and depluggedindications being returned to service. For the generator-specific distributions, the valueswere normalized to the number returned to service for that generator.


' The composite values provide a cumulative probability growth distribution for the

combined active and deplugged indications. For this analysis, the active tube growthcontribution was based on the industry-bounding distribution, and the deplugged tube

growth contribution was based on the Ref. 7 limiting growth distribution. The industrybounding data curve was needed since less than 200 plant-specific growth data pointswere available for U1R9.

There is a difference between the Table 6-6 industry bounding active growth) and

Table 6-9 (deplugged growth) voltage bin setup at the next to last voltage bin (i.e., at 3.9

volts). This was resolved by placing the Table 6-6 3.S voltage data into the 3.9 voltagefor the analysis, which provides the more conservative result.

Tables 6-10, 6-11, and 6-12 summarize the generator-specific and averaged SG

composite growth rates. Because of the heavily weighting towards the deplugged tube

growth rate, (i.e., there are a large number ofdeplugged tubes in SG 1-1 and 1-3 relativeto the small number ofactive indications), the composite growths for SG 1-1 and SG 1-3

were not bounded by the averaged SG distribution. Therefore, generator-specificcomposite growth rates were used for SG 1-1 and 1-3 and the averaged compositegrowth rate was used for SG 1-2 and SG 1-4. Figure 6-18 shows a comparison of the

composite growths, the limiting deplugged growth, and the industry-bounding growthrates in a normalized distribution.

6.7 NDE Uncertainty Distributions

NDE uncertainties must be taken into account when projecting the end-of-cycle voltagesfor the next operating cycle. The NDE uncertainties used in the calculations of theEOC-10 voltages are described in Ref. 6. The acquisition uncertainty was sampled froma normal distribution with a mean ofzero, a standard deviation of7%, and a cutoff limitof 15% based on the use of the probe wear standard. The analyst uncertainty was

sampled from a normal distribution with a mean of zero, a standard deviation of 10.3%,and no cutoff limit. These uncertainty distributions are shown in Table 6-7 and Figure6-19.


6.8 Projected EOC-10 Voltage Distributions

The EOC-10 voltage distributions were obtained by applying a Monte Carlo samplingprocess to the BOC-10 voltages. This process randomly assigns uncertainty values and

a growth value to each of the BOC-10 indications. Since the industry bounding growthdistribution discussed in Section 6.6 is in terms of delta volts per EFPY, the growthvalues from this distribution must be corrected for the expected length of Cycle 10.

Therefore, the growth values are multiplied by the expected cycle length of 1.58 EFPY.This random sampling process was performed for each BOC-10 indication in the steam

generators resulting in an EOC-10 voltage for each projected BOC-10 indication. Each

sampling ofall of the BOC-10 indications in a steam generator is called a 'trial'. Manytrials were performed and the resulting EOC-10 voltages were binned in 0.1 voltincrements. The resulting bin values were then divided by the number of trials to obtainthe average number of EOC-10 indications per trial in each voltage bin. The projectedEOC-10 voltage distributions shown in Table 6-8 and Figures 6-20 through 6-23 are

based on 1 x 106 trials.

The EOC-10 projected distributions will be compared to the actual number ofindications detected at 1R10 in the next 90 day report per Ref. 12.


Table 6-1: EOC-9 And BOC-10 Voltage Distributions For SG 1-1.

DOSs Returned to ServiceVoltage

Bin0

0.1

0.20.30.40.50.60.70.80.9

1

1.1

1.21.31.41.51.61.71.81.92

>2Total

As-foundEOC-9

00491243021

002000000001

38

POD(0.6)

0.000.006.6715.0020.006.675.000.003.331.670.000.003.330.000.000.000.000.000.000.000.001.67

63.33

RepairedTubes

DepluggedTubes

21

BOC-10

0.000.006.6722.0021.007.675.004.004.332.671.001.003.330.001.000.000.000.001.000.000.000.6781.33

Conf. ODNCC orNot Insp. w/+Pt

41612434321

1

2

Total

41613534321

1

2

56


DOSs Returned to Service

III

VoltageBin

00.1

0.20.30.40.50.60.70.80.9

1

1.1

1.21.31.41.51.61.71.81.92

>2Total

As-foundEOC-9

025

11

1810129221

0000000000 ~

072

POD(0.6)

0.003.338.3318.3330.0016.6720.0015.003.333.331.670.000.000.000.000.000.000.000.000.000.000.00

120.00

RepairedTubes

Deplug gedTubes

13

BOC-10

0.003.337.3320.3330.0018.6717.0015.002.333.334.670.000.002.000.000.000.000.000.000.000.000.00

124.00


24131711

991

24

74

Total

24131812991

24

76


able 6-3: EOC-9 And BOC-10 Voltage Distributions For SG 1-3.


BinAs-found

EOC-9POD(0.6)

RepairedTubes

Depiug gadTubes BOC-10

Conf. ODNCC orNot Insp. w/+Pt Total

00.10.20.30.40.50.60.?0.80.9

1

1.1

1.21.31.41.51.61.71.81.92

>2

0.000.000.003.3310.008.3310.006.6713.3310.003.331.671.673.330.000.000.000.000.000.000.000.00

0.000.000.004.3312.009.3313.00

1 2 7.671 14.331 11.001 4.33

1.671.67

1 4.330.00

1 1.001 1.00

0.001 1.00

0.000.000.00

Total 43 71.67 16 86.67 44 58



Bin0

0.10.20.30.40.50.60.70.80.9

1

1.1

1.21.31.41.51.61.71.81.92

>2Total

As-foundEOC-9

POD(0.6)0.000.000.003.331.673.333.333.331.670.000.000.001.670.000.000.000.000.000.000.000.000.0018.33

RepairedTubes

DepluggedTubes BOC-10

0.000.000.003.332.673.333.333.331.670.000.000.001.670.000.001.000.000.000.000.000.000.00

20.33


13

Total

13


Table 6-5: DCPP Unit 1 February 1999 Outage (1R9) Bobbin Voltage Growth Statistics for Cycle9 Active Tubes (1997 to 1999) Per EFPY.

DeltaVolts No. of Obs CPDF

Steam Generator 1-1

CPDFNo. of ObsSteam Generator 1-2 Steam Generator 1-3

No. of Obs CPDF

-0.4-0.3-0.2-0.1

0.00.1

0.20.30.40.50.60.70.80.91.0

1.2

Total

0.00.00.00.05.0

21.06.02.00.01.00.02.00.00.00.00.00.0

37.0

0.0000.0000.0000.0000.1350.7030.8650.9190.9190.9460.9461.0001.0001.0001.0001.0001.000

0.00.00.02.011.032.018.03.01.01.00.00.00.00.00.00.00.0

68.0

0.0000.0000.0000.0290.1910.6620.9260.9710.9851.0001.0001.0001.0001.0001.0001.0001.000

0.01.00.00.05.011.012.011.02.01.00.00.00.00.00.00.00.0

43.0

0.0000.0230.0230.0230.1400.3950.6740.9300.9771.0001.0001.0001.0001.0001.0001.0001.000

DeltaVolts CPDFNo. of Obs

Steam Generator 1-4CPDFNo. of Obs

Cumulative

-0.4-0.3-0.2-0.1

0.00.1

0.20.30.40.50.60.70.80.91.0

1.2

0.00.00.00.00.03.05.02.01.00.00.00.00.00.00.00.00.0

0.0000.0000.0000.0000.0000.2730.7270.9091.0001.0001.0001.0001.0001.0001.0001.0001.000

0.01.00.02.0

21.067.041.018.04.03.00.02.00.00.00.00.00.0

0.0000.0060.0060.0190.1510.5720.8300.9430.9690.9870.9871.0001.0001.0001.0001.0001.000

Total 11.0 159.0


Table 6-6: Industry Bounding and DCPP Unit I Cycle 9 Active Tube CPDF GrowthDistributions.

Voltage GrowthPer EFPY

<0.00.1

0.20.30.40.50.60.70.80.9

1.21.31.41.51.61.71.81.9

2.1

2.22.32.42.52.62.72.82.9

3.13.23.99.4

DCPP-1Cycle 9

0.15090.57230.83020.94340.96860.98740.98741.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.00001.0000

IndustryBounding

0.09540.34120.60680.81400.91570.95110.97710.98220.98220.98220.98220.98820.99410.99410.99410.99810.99840.99840.99840.99840.99880.99880.99880.99920.99920.99920.99920.99920.99920.99920.99920.99920.99960.99971.0000


Table 6-7: NDE Uncertainty Distributions.

Analyst Uncertainty Acquisition Uncertainty

ercenVariation

0

0

0

0

0

0

0

0

0

0

0

~ 0

0

0

~ 0

~ 0

0

~ 0

umu a weProbability

ercenVariation

o

0

0

0

0

0

0

0

0

~ 0

0

0

~ 0

0

~ 0

0

umu a tveProbability

~ 0

o

Std Deviation = 7.0%Mean = 00%

Cutoff =+I- 15.0%

Std Deviation = 10.3%Mean = 0.0%

No Cutoff


Table 6-8: Projected EOC-10 Voltage Distributions.

VoltageBin SG 1-1

Projected No. of Indications at EOC10SG 1-2 SG 1-4SG 1-3

0.1

0.20.30.40.50.60.70.80.9

1.21.31.41.51.61.71.81.9

2.1

2.22.32.42.52.62.72.82.9

3.13.23.33.43.53.63.73.83.9

4.14.24.34.44.5>4.5

0.02150.52081.96824.16326.81788.63178.76668.35967.18445.78734.79593.88213.17362.65432.19431.86881.60641.27250.94480.73260.66370.66700.57420.43840.33250.27910.25220.20810.23950.33300.31320.27200.28170.22900.14690.09810.07350.06030.04990.03930.02970.02190.01620.01160.0083

0.3487

0.26630.95522.69315.66729.077212.364914.126314.331413.356711.18638.95426.91845.16003.85962.88722.17371.68251.29360.94560.73010.60240.54700.49240.38960.30440.23040.19480.18030.17950.24410.28130.26170.27900.25270.18010.13170.09030.05400.03680.02880.01970.01290.00870.00520.0027

0.3614

0.00000.03090.37271.19782.56934.26716.01617.20818.30538.49458.14757.33096.22215.09084.05683.20582.56942.06541.62781.28301.01440.82930.68550.53280.42310.34030.28950.23360.17830.16890.18290.18070.18950.19880.18840.16690.13380.10880.08350.05910.04080.03010.02350.01800.0132

0.2906

0.00000.02440.22030.54560.96001.60121.87392.23102.18631.93931.63071.27820.99700.80650.66780.57690.50250.41400.33130.26160.20100.16530.12510.10200.08190.06520.05020.03440.03100.04350.04300.04330.05150.04520.03660.02800.02060.01390.00960.00760.00690.00650.00530.00390.0026

0.0627

Total 81.334281 124.001144 86.665442 20.335011


Table 6-9: First-Cycle Deplugged Tube LimitingGrowth Distribution.

DeltaVolts NormalCPDFNo. of Obs

Ref.7 - Llmltln9

-0.4 0.0 0.000 0.000-0.3 0.0 0.000 0.000-0.2 0.0 0.000 0.000-0.1 0.0 0.000 0.0000.0 2.0 0.018 0.0180.1

0.220.0 0.19824.0 0.414

0.1800.216

0.30.4

17.09.0

0.5680.649

0.1530.081

0.50.60.70.8

9.0 0.7304.0 0.7665.0 0.8115.0 0.856

0.0810.0360.0450.045

0.91.0

5.01.0

0.9010.910

0.0450.009

0.0 0.910 0.0001.2 2.0 0.928 0.0181.3 1.0 0.937 0.0091.4 0.0 0.937 0.0001.5 0.0 0.937 0.0001.6 0.0 0.937 0.0001.71.81.9

3.0 0.9641.0 0.9732.0 0.991

0.0270.0090.018

2.0 0.0 0.991 0.0002.1 0.0 0.991 0.0002.22.3

0.00.0

0.9910.991

0.0000.000

2.4 0.0 0.991 0.0002.52.6

0.00.0

0.9910.991

0.0000.000

2.72.82.93.0

0.0 0.9910.0 0.9910.0 0.9910.0 0.991

0.0000.0000.0000.000

3.1 0.0 0.991 0.0003.2 0.0 0.991 0.0003.8

9.4Total

1.0

0.0111.0

1.000

1.000

0.009

0.000


Table 6-10: SG Composite Average Growth Distribution(used for SGs 1-2 and 1-4).

Combined Average SG Growth RateDelta

VoltsDeplugged

(per Table 6-9)

Active Combined

(per Table 6-6)

Combined - CPDF

0.00.1

0.20.30.40.50.60.70.80.91.0

1.21.31.41.5

1.6

1.71.8

1.92.02.1

2.22.32.4

2.62.72.82.93.03.13.23.99.4

Total

0.99.411.28.04.24.21.92.32.32.30.50.00.90.50.00.0

0.0

1.40.5

0.90.00.00.00.00.00.00.00.00.00.00.00.00.00.50.0

52.0

15.239.142.233.016.25.64.10.80.00.00.00.90.90.00.00.6

0.1

0.00.0

0.00.1

0.00.00.10.00.00.00.00.00.00.00.00.1

0.00.1

159.0

15.346.551.339.319.69.65.83.1

2.32.30.50.91.80.50.00.6

0.1

1.40.5

0.90.10.00.00.10.00.00.00.00.00.00.00.00.10.50.0

203.0

0.0760.3050.5580.7510.8470.8940.9230.9380.9500.9610.9640.9680.9770.9790.9790.982

0.983

0.9900.992

0.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9971.0001.000


Table 6-11: Composite Growth Rate Distribution used for SG 1-1.

Combined Growth Rate for SG 1-1

Delta

VoltsDeplugged Active

(per Table 6-9) (per Table 6W)

Combined Combined - CPDF

0.00.1

0.20.30.40.50.60.70.80.91.0

1.21.31.41.5

1.6

1.71.8

1.92.02.1

2.22.32.42.52.62.72.82.93.03.1

3.23.99.4

Total

0.43.84.53.21.71.70.80.90.90.90.20.00.40.20.00.0

0.0

0.60.2

0.40.00.00.00.00.00.00.00.00.00.00.00.00.00.20.0

21.0

3.59.1

9.87.73.81.31.00.20.00.00.00.20.20.00.00.1

0.0

0.00.0

0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

37.0

3.712.413.810.55.32.91.7

0.90.90.20.20.60.20.00.1

0.0

0.60.2

0.40.00.00.00.00.00.00.00.00.00.00.00.00.00.20.0

56.0

0.0660.2880.5350.7220.8160.8680.8980.9180.9350.9520.9550.9590.9690.9730.9730.975

0.975

0.9860.989

0.9960.9960.9960.9960.9960.9960.9960.9960.9960.9960.9960.9960.9960.9961.0001.000


Table 6-12: Composite Growth Rate Distribution used for SG 1-3.

Combined Growth Rate for SG 1-3Delta

VoltsDeplugged

(per Table 6-9)

Active

(per Table 64)Combined Combined - CPDF

0.00.1

0.20.30.40.50.60.70.80.91.0

1.21.31.41.5

1.6

1.71.8

1.92.02.1

2.22.32.42.52.62.72.82.93.0

'.13.23.99.4

Total

0.32.93.52.51.31.30.60.70.70.70.1

0.00.30.1

0.00.0

0.0

0.40.1

0.30.00.00.00.00.00.00.00.00.00.00.00.00.00.10.016.0

4.1

10.611.48.9441.5

0.20.00.00.00.30.30.00.00.2

0.0

0.00.0

0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

43.0

4.313.214.611.25.62.81.70.90.70.70.1

0.20.50.1

0.00.2

0.0

0.40.1

0.30.00.00.00.00.00.00.00.00.00.00.00.00.00.10.0

58.0

0.0740.3020.5540.7460.8420.8900.9190.9350.9470.9600.9620.9670.9760.9780.9780.981

0.981

0.9890.991

0.9960.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9970.9971.0001.000


Figure 6-1: SG 1-1 1R9 As-found and BOC-10 Voltage Distributions

40

35tsAs-Found EOC-9

OCalculated BOC-10

30

25

c: 20

o

E 15

10

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 >2

Bobbin Bln Voltage

Figure 6-2: SG 1-2 1R9 As-found and BOC-10 Voltage Distributions

40

358t As-Found EOC-9

QCalculated BOC-10

30

c 25

200L

15EZ

10

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 >2

Bobbin Bin Voltage


Figure 64 SG 1-3 1R9 As-found and BOC-10 Voltage Distributions

40

35SIAs-Found EOC-9

OCalculated BOC-10

30

5 25

c: 20

0

15

K

10

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 >2

Bobbin Bln Voltage

Figure 64: SG 14 1R9 As-found and BOC-10 Voltage Distributions

40

35teAs.Found EOC-9

OCalculated BOC-10

30

g 25O

g 20

OL

E 15

R

10

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 >2Bobbin Bln Voltage


Figure 6-5: SG 1-1 & 1-2 Repaired Tube Voltage Distributions

IISG 1-1

p SG1-2

lh

O

EJ

4

0

3E2:

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 >2

Bobbin Bin Voltage

Figure 6W: SG 14 & 1R Repaired Tube Voltage Distributions

0 SG1-3

p SG1-4

5

4~t0

3ER

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 >2

Bobbin Bin Voltage


20

Figure 6-7: SG 1-1 & 1-2 Voltage Distributions of Confirmed ODSCCRemaining in Service for Cycle 10

StSG 1-1

QSG 1-2

15

cO

c 10

oI

ClER

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 >2

Bobbin Bln Voltage

Figure 6-8: SG 1-3 & 1A Voltage Distributions of Confirmed ODSCCRemaining ln Service for Cycle 10

20

15

D

�1SG1-3

OSG 144

c0

3c 10

0

E

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 >2

Bobbin Bln Voltage


20

Figure 6-9: SG 1-1 & 1-2 Voltage Distributions of ConfirmedODSCC and Uninspected DOS Indications

Remaining in Service for Cycle 10

18

16

tttSG 1-1

0SG 1-2

14

o 12

8c 10

o

8E

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 >2

Bobbin Bln Voltage

20

18

16

Figure 6-10: SG 1-3 & 14 Voltage Distributions of Confirmed ODSCC andUninspected DOS Indications

Remaining in Service for Cycle 10

st SG 1-3

OSG 1<

14

~o 12

c 10

08

E

6

III0.1 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 >2

Bobbin Bin Voltage


20

Figure 6-11: SG 1-1 & 1-2 Voltage Distributions of AllDOS IndicationsRemaining in Service for Cycle 10

18

16

1SG 1-1

OSG 1-2

14

12

8a 10

O

8E

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 >2

Bobbin Bin Voltage

20

Figure 6-12: SG 1-3 8 14 Voltage Distributions of AllDOS IndicationsRemaining ln Service for Cycle 10

18

18

QSG1 3

OSG 1<

14

~o 12

10

OI

8E

6

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 >2

Bobbin Bln Voltage


40

Figure 6-13: SG 1-1 & 1-2 Delta Voltage Per EFPY Growth Distributions of BobbinIndications Detected During Cycle 9

35t3SG 1-1

QSG 1-2

30

25

O

c 20s0I

15

10

o Q ls 0> 'b s + 4 0> 'b

Bobbin Bin - Delta Voltages Per EFPY

Figure 6-14: SG 1-3 8 1s4 Delta Voltage Per EFPY Growth Distributions of BobbinIndications Detected During Cycle 9

40

35laSG 1s3

OSG 1s4

30

o 25

200s

15E

10

q, I rp 'b

Bobbin Bln - Delta Voltages Per EFPY

FTI NonsProprietary 50 86-5003756-00

Figure 6-15: ARC industry Growth Rate (CPDF) Curves with a Bounding Curve

1.1000

1.0000

0.9000

0.6000

0.7000

0.6000

0.6000

0.4000

0.3000

0.2000

~PnnlU1 - Cl

~PIG'S Ul ~ C2~ SSnnl Ul ~ CS

~MU1 C4

~PUnlU2 Cl~ Plnnl U2 ~ C2~ Plnnl US ~ C2

Plnnl US ~ CS—PlnnlUS ~ C4

~PlnnlU4 Cl

-SS-Plnnl U4 ~ C2

~PUnlUS C9

~Plan US ~ C10~ Plant US ~ C1 1

~DCPP U2 ~ CS

~DCPP Ul ~ CO

0.1000

0.0000

~b ~b ~n ~< ~b ~42 g ~% ~'p ~b ~42 ~A ~<5 ~< ~b

Delta Veltage Change


1.1000

Figure 6-16: DCPP Unit 1 Cycle 9 Active Tube Growth Rate (CPDF) CurveCompared with the industry-Bounding Curve and DCPP Unit 2 Cycle 8.

1.0000

0.9000

0.8000

0.7000

~ DCPP U1 ~ C9~ DCPP U2 ~ CS~ SouncAny

0.6000OQ

0.5000

0.4000

0.3000

0.2000

0.1000

p<b ~A ~<) ~'9 ~4 o'P o'9 ~b oA o% ~'P ~'b ~S ~A ~9 ~4 ~b

Delta Voltage Chango


0.50

Figure 6-17: Normalized DCPP Unit 1 Cycle 9 Growth Distribution Compared toindustry Bounding and DCPP Unit 2 Cycle 8

0.45

0.40

0,35OFo 030O

O 0.25

O

0.20

5O 0.15X

-ts-Diablo Canyon U2 - CS

~ Diablo Canyon U1 - Cg

~ Industry Bounding

0.10

0.05

0,00

~b ~4 O4 Ob Ob OA Orir ~4 ~b ~S ~A ~% ~4 ~b ~S ~A ~B

Delta Voltage Change

Kiri


0.5

Figure 6-18: Normalized SG Averaged Combined 1R9 Growth RateDistribution Compared with SG 1-1 and SG 1Q

0.45

0.4

0.35O

0.3OOX

0.25

0,2

o 0.15

~SG 1-1 (Comb.)~ SG 1D (Comb.)

~SG Average (Comb.)~ Industry Bounding (Active)~ Ret. 7 Limiting (Depiugged)

0 0.1 0.20.30.4 0.5 0.60.70.80.9 1 1.1 1.21.3 1.4 1.51.61.71.81.9 2 2.1 2.22.32.42.52.6 2.72.82.9 3 3.1 3.2

Delta Voltage Change


Figure 6-19

1.0

NDE Uncertainty Distributions

0.9

0.8

Analyst Uncertainty—Acquisition Uncertainty

0.7

0.6

a 0.5

0.4

0.3

0.2

0.1 .

o.o .

Percent Variation In Voltage

-4P.P% -3Q.P% -2P.Q% -1P.P% P.P% 1P.P% 2Q.P% 3Q.P% 4P P%


Figure 6-20: SG 1-1 Projected EOC-10 Voltage Distributions

40

35

30

OCalcutated BOC-10

ttt Projected EOC-10

c 25

O

c 200

E 15

10

v v v vBobbin Bin Voltage


40

3530'Calcutated BOC-10

St Projected EOC-10

o 25j20

oI

15E

Z10

Cv 0 0 0 0 ~ ~ 4'''' 'V + + 'b 'b 6 'O'Pb''obbin

Bin Voltage



40

35

30

OCalculated BOC-10

tIProjected EOC-10

a 25O

3c 20

~\0

15

R

10

0

Ob O<P O% O% 4 'b 0 ~A 9 4 5 5 ~ ra 4 g 4p ~ cb 4 5 4)

Bobbin Bln Voltage

Figure 6-23: SG 14 Projected EOC-10 Voltage Distributions

40

35

30

0 Calculated BOC-10

@Projected EOC-10

c 25

O

c: 20.0

15E

10

Ob Ob O% ra 'P 'b ~<0 ~% ~O ~4 ~b ~9 0 ~% 4 ~b ~<o ~% ~rb ~4 PBobbin Bln Voltage


7.0 Database Applied for Leak and Burst Correlations

The leak and burst correlations utilized in the analyses presented in this report are based on theAddendum 2 1998 Database Update (Ref. 7) for the voltage-based repair criteria for 7/8 inch

tubing. The leak rate correlations used were developed for a MSLB delta P of 2560 psi. Thecorrelations have been developed specifically for the evaluation of ODSCC indications at TSPlocations in Model 51 steam generators and relate bobbin voltage amplitudes, free span burstpressure, probability of leakage and associated leak rates to assess end of next cycle structuralintegrity.

7.1 Conditional Probability ofBurst

For the burst pressure versus voltage correlation, the database contained in Ref. 7 meetsall GL 95-05 requirements and was used in these calculations. Material properties werealso considered as part of the calculations and were obtained from Ref. 6. The FTIMonte Carlo computer code was utilized to predict the POB at the end of cycle 10 based

upon the input parameters shown in Table 7-1 (from Ref. 7, Table 6-5). This simulationfollows the statistical methods presented in Ref. 6.

Table 7-1Tube Burst Pressure vs. Bobbin Amplitude Correlation

P. = ai+ ui log(Volts)

Parameter

<ErrorN (data pairs)

p Value for cdReference o'

Database

7.58911-2.40111

S2.7%0.82652

85

1.20x1068.78

Adjusted Input8.27517-2.61817

82.7%0.90124

851.20xl0"

75.0

Note:(1) The slope and intercept coefficients and the standard error value from Ref. 7 were adjusted for a

reference fiow stress of75.0 ksi by multiplying those input terms by 1.0904.


7.2 Conditional Leak Rate

Ref. 7 presents the results of the regression analysis for the voltage-dependent leak ratecorrelation using the updated leak rate database for 7/8" tubes mentioned above. It is

showh that the one-sided p-value for the slope parameter in the voltage dependent leakrate correlation is 3.5% which is below the 5% threshold for an acceptable correlationspecified in Generic Letter 95-05.

The methodology used in the calculation of these parameters is consistent with the NRCcriteria in Ref. 1. The POL and leak rate correlation parameters used in this analysis are

shown in Tables 7-2 and 7-3. The inputs are taken directly from Ref. 7, Tables 6-6 and6-7.

Table 7-27/8" Tube Probability ofLeak Correlation (2560 psi)

Pr(Leak) = {I + e-I.PI+V. log(V)]}-I

Parameter

V12V22DoFDeviancePearson SD

Database-4.262724.167460.68535-0.603650.60210

130

78.6776.6%

Notes:

(l) Parameters Vi] are elements of the covariance matrix of the coefficients, Pj, of the regression

equation.

(2) Degrees offreedom.

i


Table 7-3Leak Rate Database for 7/8" Tube ARC Applications

bj + b4 xlog(volls))q -10

Parameter Database

Intercept, b3Slope, b4Index ofDeter, rResiduals, aptYor (b5)Data Pairs, NMean ofLog(V)SS ofLog(V)p Value for b4

-0.5268820.987179

11.7%0.808109

291.154372.39739

3.5%

ieFTI Non-Proprietary 60 86-5003756-00

.0 Tube Integrity Method and Evaluations

The Monte Carlo analyses used to calculate the SLB leak rates and tube burst probabilities forthe projected EOC-10 voltage distributions are consistent with the methods used in Ref. 6. TheFTI simulation analysis methodology is described in Refs. 4 and 5. In general, the methodologyinvolves application of statistical correlations for burst pressure, probability of leakage and leakrate to a measured or calculated EOC distribution to estimate the likelihood of tube burst and

primary-to-secondary leakage during a postulated SLB event. The Monte Carlo analyses

account for correlation parameter uncertainties associated with burst pressure, leak rate

probability, and leak rate, which are explicitly included by the sampling process. NDE and

material property uncertainties are also similarly included.

This section presents the results of analyses carried out to predict leak rates and tube burstprobabilities for postulated SLB conditions for the projected EOC-10 voltage distributions. SG1-2 and SG 1-3 with the largest total number of indications and the largest number ofindications over 1 volt are expected to yield the limiting SLB leak rates and burst probabilitiesfor Cycle 10.

8.1 Leak Rate and Tube Burst Probability for EOC-10

Calculations to predict SLB leak rate and tube burst probability for each steam generatorin DCPP Unit-1 at the EOC-10 conditions were carried out using the NRC-requiredconstant POD value of 0.6 and the combination of a very conservative industry-bounding growth rate distribution for active tubes and a very conservative limitinggrowth rate distribution for deplugged tubes. The leak and burst results for each steam

generator are given in Table 8-1.

The limiting EOC-10 SLB leak rates, 0.2754 and 0.2758 gpm (room temperature), waspredicted respectively for SG 1-2 and SG 1-3. Each of these generators had a largenumber of indications as well as a large percentage of deplugged tube indications beingreturned to service for Cycle 10 operation. This limiting leak rate value remained at twoorders of magnitude below the allowable SLB leakage limit of 12.8 gpm. It should be

noted that this overall plant limit has not been adjusted for leakage contributions fromother ARCs that have been implemented during U1R9

The limiting tube burst probability, 3.09 x10, was predicted for SG 1-2. It also is two-2

orders ofmagnitude below the NRC reporting guideline of 10


8.2 Summary and Conclusions

The requirements for burst probabilities are met at EOC-10 with no steam generatorexceeding the lx10-2 criteria. For the leak rate, the plant-specific value of 12.8 gpm (atroom'emperature) for the faulted steam generator was not exceeded for any steam

generator.

i



Summary of Calculations of Tube Leak Rate and Burst Probability at fOC-10for 1 million Simulations

SteamGenerator POD

Numberof indicationsat EOC-10 (1)

Bestfstimate

95% UCL(1 or MoreFailures)

Probability of BurstSLBLeak

Rate (3 5)

(gpm)

0.6 81.33 2.120 x 10" 2.376 x 10 0.2102

1-2

1-3

1-4

0.6

0.6

0.6

124.00

86.67

20.34

2.800 x 10

2.230 x 10

5.300 x 10

3.091 x 10"

2.492 x 10

6.663 x 10

0.2754

0.2758

0.0382

Acceptance Criteria 1.0 x 10 12.8(6)

Notes: (1) Adjusted for POD.

(2) Best Estimate is the number oftrials with a failure divided by the number oftrials.

(3) Equivalent volumetric rate at room temperature.

(4) The 95% Upper Confidence Limit(UCL) is based on the number of trials with one or more failures.

(5) The calculated total leak rate reflects the upper 95% quantile value at an upper 95% confidence bound.

(6) This limithas not been adjusted for leakage contributions from other ARCs that have been

implemented during U1R9.


9.0 References

1. NRC Generic Letter 95-05, "Voltage-Based Repair Criteria for the Repair ofWestinghouse Steam Generator Tubes Affected by Outside Diameter StressCorrosion Cracking," USNRC Office of Nuclear Reactor Regulation, August 3,1995.

2. NRC SER for Diablo Canyon Units 1 and 2 for Voltage-Based Repair Criteria,letter to PG&E dated March 12, 199S.

3. FTI Document 86-5003633-00, "DCPP Unit 1 1R9 Return-to-Power Simulation,"March 1999.

4. FTI Document 51-5001160-00, POB Simulation - POB97vb.F90, March 1998. ~

5. FTI Document 51-5001151-00, POL Simulation - LKR97vb.F90, March 1998.

6. WCAP 14277, Revision 1, SLB Leak Rate and Tube Burst Probability AnalysisMethods for ODSCC at TSP Intersections, December, 1996.

7. EPRI Report NP 7480-L, Addendum 2, 1998 Database Update, "Steam GeneratorTubing Outside Diameter Stress Corrosion Cracking at Tube Support PlatesDatabase'for Alternate Repair Limits," Electric Power Research Institute, April1998.

8. Pacific Gas and Electric Company, Diablo Canyon Power Plant Unit 1, "DataAnalysis Guidelines", Revision 2, February 18, 1999.

9. Pacific Gas and Electric Company, Diablo Canyon Power Plant, Surveillance TestProcedure, STP M-SGTI, Revision 1, "Steam Generator Tube Inspection."

10., FTI Document 51-5003835-00, ARC Probe Wear Monitoring for Diablo Canyon-Unit 1R9, May 1999.

11. FTI Document 51-5003036-00, "50.59 Input for Using Changeable Feet Probes atDCPP, February 1999.

12. NRC Letter to NEI, dated February 9, 1996, Probe Wear Criteria.

13. Pacific Gas and Electric Company, Diablo Canyon Power Plant, PlantEngineering Procedure PEP R-5, "Burnup Tracking".

14. FTI Document 86-5001354-00, "DCPP Unit 2 2RS 90 Day Report," June 1998.


Enclosure 3PG8 E Letter DCL-99-076

SPECIAL REPORT 99-04

DESTRUCTIVE EXAMINATIONSUMMARYREPORTGENERIC LETTER 95-05 VOLTAGE-BASEDREPAIR CRITERIA

DIABLOCANYON POWER PLANTUNIT 1 NINTH REFUELING OUTAGE

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