ML17312B335

Summary of 970220 Meeting W/Aps to Discuss Results of SG Tube Current Insp Particularly as They Relate to Issue of Appropriate Cycle Length for Plant,Unit 2

ML17312B335
Person / Time
Site:	Palo Verde
Issue date:	03/25/1997
From:	Thomas C NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
TAC-M91818, NUDOCS 9703260277
Download: ML17312B335 (92)

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&0001 March 25, 1997 LICENSEE:

Arizona Public Servic>>

Company FACILITY:

Palo Verde Nuclear Generating Station

SUMMARY

OF MEETING HELD ON FEBRUARY 20,

1997, TO DISCUSS STEAM GENERATOR ISSUES On February 20, 1997, the NRC staff met with representatives of Arizona Public Service Company (APS) to discuss results of the steam generator tube eddy current inspection, particularly as they relate to the issue of an appropriate cycle length for Palo Verde Unit 2.

Matters discussed included structural and leakage integrity analyses supporting the operating length of Cycle 7 of Unit 2 and the Palo Verde steam generator tube degradation management program.

Persons attending the meeting are listed in Attachment l.

Viewgraphs presented at the meeting are listed in Attachment 2.

The licensee gave a brief introduction describing the root cause of the dominant degradation mechanism affecting the steam generator tubes at Unit 2 (i.e., free-span, axially oriented, outside-diameter stress-corrosion cracking),

along with a summary of major changes and improvements in their tube integrity program since the steam generator tube rupture in March 1993.

The licensee also discussed its inspection program and the results of its structural and leakage integrity analyses for the steam generator tubes.

These analyses included a condition monitoring assessment (from the as-found condition of the steam generator tubes) and an operational assessment (from the projected end-of-Cycle 7 inspection results).

Much of the material presented at the meeting had previously been submitted to the staff in the Unit 2 report dated January 3,

1997.

The licensee concluded that Unit 2 could be operated until the next scheduled refueling outage at the end of Cycle 7 (approximately 16.5 months of operation) on. the bases of analyses presented in the January 3,

1997, report.

This report stated that the structural and leakage integrity of the Unit 2 steam generators would be maintained until the scheduled refueling at the end of Cycle 7.

These analyses are similar to those used by the licensee to assess a full cycle of operation for Unit 3.

This full cycle of operation for Unit 3 (approximately 15 to 16 months) ended in February 1997.

Similar analyses had been used to assess the previous operating interval of 12 months (a full cycle of operation) for Unit 2.

The staff did not identify any significant concerns with the licensee's conclusion about the Unit 2 operating cycle length during the meeting;

however, since the staff has not reviewed the probabilistic methodology used by the licensee in detail, the staff requested that the licensee submit the inspection results from the Unit 3 outage (which commenced in February 1997) to provide further assurance that the probabilistic methodology conservatively predicted the end-of-cycle conditions for Unit 3.

Since the methodology used for Unit 2 is similp~@~t used for Unit 3, conservative results for Unit 3

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would provide added confidence that 'the predictions for'nit 2 would also be conservative.

The results to, be submitted from the Unit 3 steam generator tube inspection outage are a comparison of the projected end-of-cycle conditions to the as-found condition.

In addition to the above, the staff obser'ved at the end of the meeting that the licensee appeared to be relying heavily on eddy current examination results with no independent evaluation of these results (e.g.,

through the periodic removal of tubes, complemented by the performance of in situ pressure testing).

ORIGINAL SIGNED BY Charles

Thomas, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos.

STN 50-528, STN 50-529, and STN 50-530 Attachments:

1.

List of Attendees 2.

Viewgraphs cc w/atts:

See next page R

TRIRTINTTA<<

I AIT Docket File

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PUBLIC" JClifford CThomas OGC'CRS

'-MAIL (w/Att 1)

SCol 1 ins/FMiragl i a TSul 1 ivan RZimmerman KKarwoski JRoe CBeardslee EAdensam WBateman EPeyton DRoss (e-mail to SAM)

MBiamonte AHowell, Region IV DOCUMENT NAME:

PV0220.MTS PDIV-2 Reading

KPerkins, WCFO OFC PDIV-2 LA PDIV-2/PM EMCB NAME EPeyto CThomas JStr nider DATE 3/~ 96, 3/ =@96 OFFICIAL RECORD COPY 3

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t would provide added confidence that the predictions for Unit 2 would also be conservative.

The results to be submitted fr'om the Unit 3 steam generator tube inspection outage are a comparison of the projected end-of-cycle conditions to the as-found condition.

In addition to the above, the staff observed at the end of the meeting that the licensee appeared to be relying heavily on eddy current examination results with no indeperident evaluation of these results (e.g.,

through the periodic removal of tubes, complemented by the performance of in situ pressure testing).

Docket Nos.

STN 50-528, STN 50-529,

.and STN 50-530 Charles

Thomas, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Attachments:

I-.

List of Attendees 2.

Viewgraphs cc w/atts:

See next page

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Mr. Steve Olea Arizona Corporation Commission 1200 W. Washington Street Phoenix, Arizona 85007 Douglas Kent Porter Senior Counsel Southern California Edison Company Law Department, Generation Resources P.O.

Box 800

Rosemead, California 91770 Senior Resident Inspector USNRC P. 0.

Box 40

Buckeye, Arizona 85326 Regional Administrator, Region IV U. S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064

Chairman, Board of Supervisors ATTN:

Chairman 301 W. Jefferson, 10th Floor

Phoenix, Arizona 85003 Mr. Aubrey V. Godwin, Director Arizona Radiation Regulatory Agency 4814 South 40 Street

Phoenix, Arizona 85040 Ms. Angela K. Krainik, Manager Nuclear Licensing Arizona Public Service Company P.O.

Box 52034

Phoenix, Arizona 85072-2034 Mr. John C. Horne, Vice President Power Supply Palo Verde Services 2025 N. Third Street, Suite 220

Phoenix, Arizona 85004 Mr. Robert Burt Los Angeles Department of Water

& Power Southern California Public Power Authority 111 North Hope Street, Room 1255-B Los Angeles, California 90051 Mr. David Summers Publ ic Servi ce Company of New Mexico 414 Silver SW, ¹0604 Albuquerque, New Mexico 87102 Mr. Bob Bledsoe Southern California Edison Company 14300 Mesa

Road, Drop D41-SONGS San

Clemente, California 92672 Mr. Robert Henry Salt River Project 6504 East Thomas Road Scottsdale, Arizona 85251 Terry Bassham, Esq.

General Counsel El Paso Electric Company 123 W. Mills El Paso, Texas 79901 Mr. James M. Levine Executive Vice President, Nuclear Arizona Public Service Company Post Office Box 53999

Pgoenix, Arizona 95072-3999

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List of Attendees Arizona Public Service Com an Bill Ide Phil Gray Ooug Hansen Jo Provasoli Rodney Wilfred Scott Bauer Rich Schaller Kevin Sweeney A tech En ineerin Jim Begley Brian Woodman NRC Ted Sullivan

-Ken Karwoski Cheryl Beardslee Charles Thomas

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Attachment 2

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1 V GS Steam Ge erator Iss es Meet iew ra hs

Palo Verde Nuclear Generating Station Unit 2 Cycle 7 Steam Generator Assessment February 20, 1997

Agenda k

> Introduction - R. Schaller

> Inspection Program - D. Hansen

> Condition Monitoring - K. Sweeney

> Operational Assessment

- J. Begley

> Degradation Management - K. Sweeney

> Summary - R. Schaller

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0 Introduction Richard Schaller Manager APS Steam Generator Projects

Introduction k Participant Introductions k Background Upper Bundle ODSCC

~ Small defects difficultto detect with

, standard bobbin coil

~ Distinct defect pattern (ARC)

First observed in U2R3 - Fall 1991

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Led to tube rupture at end of Cycle 4-March 14, 1993 APS actions

~ Root Cause Analysis

~ Inspection technology and scope improvements

~ Predictive modeling

~ Remedial actions

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Introduction

> Major Changes / Improvements Large scale tube pull programs Extensive RPC inspection programs In-situ pressure testing Thermal-hydraulic modeling Boric Acid Treatment Thot Reduction Secondary Chemistry Improvements Chemical Cleaning SG Modification ns Conservative Leak Monitoring and

Response

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Introduction

> Predictive Models ATHOS Bounding Model

~ Theoretical Link to Corrosion

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• Empirical Validation Multiple Cycle Crack Simulation Model

~ Simulates corrosion process and defect management program Crack initiation Crack growth Crack morphology Inspection and Repair

~ Model provides for Condition Monitoring Assessment

~ Projections consistent and conservative

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Introduction

> PVNGS Steam Generator Status Last Meeting 9/20/95 No forced shutdowns since 1993 Unit 1 Full Cycle Operation

~ No cycle restrictions Unit 2 - Full (12 month) Cycle 6 Unit 3 - Full (16.5 month) Cycle 6' Unit 2 commenced Cycle 7 operation on 5/3/96

0 Inspection Program Doug Hansen APS Level III

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~4 PVNGS SG Inspection Program.

> Purpose Detect and remove from service critical

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tube defects

~ Conservative plugging criteria

~ All detected SCC defects plugged Implementation State-of-the-art equipment and techniques Data analyst training Strong utilityoversight Performance demonstration and trending Conservative inspection scope and expansion criteria

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ECT Techniques

> APS employs "best available" techniques for PVNGS SG damage mechanisms First production application of Plus Point Probe - December 1994 Plant specific tube pull data integrated into ECT program

> Techniques are EPRI Appendix H qualified (or equivalent) for detection

> Quantitative and qualitative data quality requirements implemented

> No sizing or threshold criteria for SCC Plug on detection

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~4 ECT Analysis

> All analysts EPRI QDA qualified includes two (2) QDA's on staff

> Site Specific Performance Demonstration PVNGS ECT Guidelines and Training Bobbin Coil and Plus Point Practice Data

~ Supported by tube pull data Examination required

> Primary/Secondary analysis teams from separate companies

> Analyst trending by APS Level III

> Resolution Analyst requirements "Super Resolution"

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U2R6 ECT SCOPe

> ECT Scope and Purpose 100% Full Length Bobbin Coil

~ Tube condition screening 100% + Point of HL TTS expansions

~ Detection of circumferential and axial SCC

~ Generic Letter 95-03 5% + Point of CL TTS expansions

~ Detection of SCC defects

~ Industry experience 100% + Point of Row 1 and 2 U-bends

~ PVNGS and Industry experience Examine historical >20% bobbin wear

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VVith +Point - determine ifSCC is present 100% + Point of ARC Region Outside ARC Region sample

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+ Point, region verification

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~ 5 ECT Expansion Criteria

> Axial SCC Indications

+ Point Five tube buffer zone in all directions

+ Point inspection of all bobbin indications which exceed PVNGS plugging criteria

~ Additional confirmation

+ Point inspection of all Bobbin I-codes

> Circumferential SCC Indications 100'/0 of CL TTS expansions ifone circumferential defect is identified

ECT Results - SG 2-1 Eddy Current Call 20-29%

30-39%

>40%

I-Code" NBI TBP Remarks Wear and Small Imperfections 553 177 10 9

8 >40%

1 - BW Stay 2 > 40% also SVI Axial Indications (SAI/MAI)

Circumferential Indications (SCI/MCI)

Volumetric Indications (SVI/MVI)

PLI 98 100

1TSH, 1Row 1

98 ARC NA 8

AllTSH 2

01C Total 123 Note 7 additional preventatively

, plugged at patch "plate - Total plugging - 130 14

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Eddy Current Call 20-29%

30-39%

>40%

"I-Code" NBI TBP Remarks Wear and Small Imperfections 724 266 24 23 21 >40%

2-BW Stay 2>40% also SAI 1 > 40% - PLI Axial Indications (SAI/MAI)

Circumferential Indications (SCI/MCI) 154 158

7TSH, 101H 150 - ARC NA 3

AllTSH Volumetric Indications (SVI/MVl)

PLI 1

01C Total 188 1 additional tube plugged due to OBS Total plugged 189

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Condition Monitoring Assessment Kevin Sweeney APS Steam Generator Projects

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Condition Monitoring Assessment

> Draft Reg Guide, Section C.3.0 states that licensees should monitor the as-found condition of SG tubing to verify compliance with performance criteria Structural Integrity Operational Leakage Accident induced leakage

> APS approach Compare measurable ECT information with EOC 6 predictions

~ Number of defects

~ Structurally significant crack length

~ MRPC voltage/depth

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Condition Monitoring

> Model Description

. APS developed means to assess steam generator tube integrity in presence of a unique stress corrosion cracking phenomena

~ Assessment required a quantitative result regarding number and size of cracks at end of operating period

~ IVlethodology must be benchmarked to relevant field experience Basic mechanistic model preferred

~ Crack process simulated

~ Each component verifiable Multiple cycle model

~ Responds to evolving conditions Process has produced consistent and conservative results for PVNGS

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Condition Monitoring

> Number of ARC Region cracks Structural integrity analysis dependent on predicting the number of undetected and uninitiated cracks at BOC 6 that become detectable at the EOC 6 0.15 0.12 0.09 0.06 0.03 500 530'60 590 620 650 680 710 740 770 800 NUMBEROF CRACKS - U2R6 (PLUS POINT)

Cracks detected U2R6 = 286 19

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Assessment

> Projection clearly conservative

> APS/APTECH assessed over-estimate POD effects

~ Simulated vs Actual Multi-population effects "Shutdown" of initiation process Growth rate reduction

> Assessment indicated strong correlation with growth rate reduction Attributed to remedial measures employed at PVNGS

~ Chemical cleaning

~ Thot reduction

~ Secondary Chemistry improvements 20

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Plus Point POD 1.0 0.8 I

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O0 0.6 0.4 0.2 0.0 0

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20 40 DEPTH 60 80 PLANT C 100

> PV-2 Comparison of Simulated Plus Point POD with Recent Tube Pull Data for Upper Bundle Freespan ODSCC 21

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~r Crack Benchmark Cycle 6 Growth Rates 160 140 120 0

100 80 60 0

40 20 P.

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286 Cracks detected 0

5 225 235 245 255 265 275 285 295 305 315 325 335 345 355 230 240 250 260 270 280 290 '00 310 320 330 340 350 360 NUMBER OF DEFECTS - U2R6 22

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~ i Crack Length

> Crack Length Distribution Not a projection Little change from cycle to cycle, unit to unit Input distribution to structural limit simulation

> Probe Characteristics From tube pull data, APS found that Q.115 coil detected length was a reasonable estimate of structurally significant crack length Plus Point Impact

~ Plus Point lengths overly conservative

> Assessment Compare crack length distributions 23

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RPC Crack Length 2.50 2.00 UJzOz zI-(3 1.50 UJ O

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CL 0.50 0.00 0.00 0.50 1.00 1.50 2.00 2.50 STRUCTURALLYSIGNIFICANTCRACK LENGTH, INCHES 24

RPC Crack Length Comparison Distribution of Unit 2 Crack Lengths 1.00 0.90..

0.80 0.70..

Q L

0.60..

U 0.50 0.40..

0.30..

6$

0.20..

0.10..

~ U2R6

~ U2R5 0.00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 g CO bl CD 0 0

CQ CV CD 0 0 CO CV CD 0 0 0 0 t- <

bl N

N C9 CO 4 0 rF LO CD CD Length (in) 25

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Voltage/Depth

> No validated sizing technique Plug on detection

> PVNGS Voltage-to-depth correlation developed from tube pulls 31 tubes removed from Unit 2and 3 0.115 pancake coil voltage Correlation has been consistent for monitoring growth rather than absolute depth Supported by In-situ testing

> Sizing Checkpoints In-situ test candidate.> 2 volts Exceedance criteria > 2.25 volts

> Largest defect in U2R6 - 1.23 volts 26

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VoltagelDepth

> Model predicted no through-wall leakers Through-wall defect an indicator of severity No indication of leakage

> Predicted vs observed voltages Measurable ECT parameter for condition monitoring Observed results bounded by model predictions 27

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Voltage Distribution EOC 6 1.0 0.8---

m 0.6-0K 0.4 '

0.2-0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 EOC 6 VOLTAGE-VOLTS Predicted Observed 28

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Condition Monitoring Summary

> As-found condition of Unit 2 steam generators satisfies all structural and leakage performance criteria

> Condition monitoring performed on measurable inspection criteria

> Modeling techniques provide consistent and conservative results for all PVNGS units

Operational Assessment Dr. Jim Begley APTECH 30

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Probabilistic Methodology

> Four major elements modeled Crack initiation Crack propagation Crack detection Structural limitevaluation

> All elements have significant variational as well as deterministic components

> Solution requires advanced probabilistic methodology

> Monte Carlo simulation Analog process-deterministic simulation with variation Major components modeled with

. distributions

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Simulation Process

> Each major component describable by appropriate probability distribution function (pdf)

> Crack initiation - Weibull

> Crack propagation rate - Log-normal

> Crack detection - Sigmoidal or ramp

> Tube structural limits - Output pdf from simulation involving:

As-built material mechanical properties Crack length pdf Burst pressure correlation

~ Modified Framatome correlation 32

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I Model ImprovementslValidation

> Form Factor Crack morphology effects

>.Crack Growth Rates Direct Sampling Variational cycle to cycle

> Benchmarking - voltage Measurable ECT parameter Assessment of measurement errors 33

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Form Factor W14 5

3 9

2.0 1.0 1.4 2.5 1.6 0.66 Spectrum of Axial Crack Profiles

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V Form Factor Tube ID Tube OD Cusp-Like Crack Profile Drawn to Scale 35

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Form Factor DISTRIBUTIONOF FORM FACTOR 80 e)0 CY C4 40 20 0

1.8 FORM FACTOR - DMAX/DSTR 36

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Crack Growth Rate Q

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g~8 O

Cl 5 )

0 20 %.10 0.00 0.10 0.20 0.30 0.40

%.50.0.40 4/M 4I.

41.45 %.35 <.25 4I.15 4I.OS 0.05 0.15 0.25 0.35 0.45 Expecte VOLTAGEGROWTH ~ dV/dT 3113579 11 13 15 17 19 21 23 25 27 29 31 33 35 37

~2 0 2 4 8

8 1012141818202224282830323438 DEPTHIVOLTAGE-dD/dV 1'IO 100 GROWTH RATE DISTRIBUTIONFUNCTION 80 70 60 50 40 30 20 10 2

0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 GROWTH RATE - dD/dT 37

Results

>'rojections and Benchmarks 112 INSPECTION ~ V2RT (PRDJECTEDi 96 88 72 48 40 32 N

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0 eerr 220 225 230 235 240 245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 NUMBER OF CRACKS OBSERVED 135 126 117 10S 99 81 V) 63 45 3S 27 18 9

INSPECTION - U2R6 0

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230 235 240 245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345 350 NUMBER OF OBSERVATIONS 38

Results Projection's and Benchmarks 154 INSPECTION ~ U2MS 2 143 132 co 121 O

110 P

99 5

88 77 66 O

55 33 22 11 0

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220 225 230 235 240 245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 NUMBER OF CRACKS OBSERVED INSPECTION U2RS 140 130 120 110 100 o

50 m

40 30 20 10 4r e

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0 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 NUMBEROF CRACKS OBSERVED 39

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EOC Voltage Projection EOC 7 Voltage Projection 1.0 0,8 g

0.6 0

5 0.4 0,2

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0,0 0,0 0.2 0,4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 RPC MEASUREMENT-VOLTS EOC 6 Voltage Projection 1,0 0.8 g

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0.2 0.0 0.0 0 2 0.4 0 6 0 8 1,0 1,2 1,4 1,6 1,8 2,0 EOC 6 VOLTAGE~ VOLTS 40

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Results

> Structural Integrity Performance Criteria

~ Conditional Probability of tube rupture at MSLB < 102

~ Low probability of Reg Guide 1.'i 21 exceedance Results - 16.5 month run time

~ Upper 95% confidence for MSLB - 3x10~

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Reg Guide exceedance

- 4x10~

> Leakage Integrity Chance of leaking ARC region crack at normal operation or MSLB -4x10 '

Model benchmarked against previous outage results

> Independent assessment in agreement

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Degradation Management Kevin Sweeney Steam Generator Projects 42

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PVNGS Degradation Management

> Program developed following the discovery of ARC Region ODSCC

> Program consistent with the draft SG Rule Preventative measures to reduce degradation

~ Chemical cleaning

~ Thot reduction

~ Secondary chemistry improvements

~ ~ SG modifications Comprehensive ISI program

~ Use of Plus Point since 1994

~ Supported by tube pull data Conservative plugging program

~ Plug SCC defects on detection

~ Critical wear mechanisms plugged at 20%

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Plug Results Plugging results bounded by preoutage projections Damage Mechanism Arc Region 515 248 Plug Projection Plug Actual Circumferential Cracks Axial Cracks Lower Bundle Other (Wear, PLP) 45 25 90 Preventative Plugging

. Total 675 319 Plugging totals SG 22 1379 or 12.5'lo SG 21 550 or 5.0'/o 44

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> Prescriptive measures Conservative leakage monitoring

~ More conservative than EPRI

~ Limits on RCS activity Operator training

~ Response to tube leakage and rupture events Consistent and conservative analysis techniques

~ Demonstrated via condition monitoring and benchmarking Active industry role

~ CEOG

~ EPRI/NEI Rulemaking response

~ Technology Transfer Program with EdF

~ lNPO Evaluation participants 45

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Program Application

> Program works and is evolutionary ISI program adjustments

~ Integration of PVNGS inspection results

~ Industry integration Leakage monitoring

~ Heightened awareness

~ Leakage response Analysis Improvements Self Assessment 46

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ARC Region Scope Verification k APS active in following recent CE plant observations of freespan cracking CEOG activities ECT Program best indicator of the validity of T/H models

> PVNGS ARC Region Verification Location of defects consistent through twelve (12) PVNGS inspections Outside ARC sample program employed Buffer zone program 100% Bobbin Coil exam employed

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Bobbin POD adequate for problem defects

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All I-codes are re-examined with Plus Point

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Bobbin wear calls examined k Program works Led to expanding standard extent to 07H 8 second VS 47

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S UlTllllary Richard Schaller Manager Aps Steam Generator projects 48

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Summary

> High confidence that structural and leakage integrity for Unit 2 Cycle 7 will be maintained U2R6 results bounded by EOC 6 predictions Analysis indicates reduction in corrosion rates Operational Assessment performance criteria satisfied

> PVNGS SG Degradation Management provides defense-in-depth

> Full cycle operation justified for Cycle 7 49

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