ML16342D607

Summary of 970410 Meeting W/Pg&E to Discuss Alternate SG Tube Repair Method Involving Locked Tube Support Plates. List of Attendees & Handout Encl

ML16342D607
Person / Time
Site:	Diablo Canyon
Issue date:	05/01/1997
From:	Steven Bloom NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
NUDOCS 9705050045
Download: ML16342D607 (56)

Text

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1997 I

LICENSEE:

Pacific Gas and Electric Company FACILITY:

Diablo Canyon Nuclear Power Plant

SUMMARY

OF MEETING HELD ON APRIL 10,

1997, WITH PACIFIC GAS 8L ELECTRIC (PG8LE)

TO DISCUSS MODEL 51 STEAN GENERATOR LOCKED,TUBE SUPPORT PLATES The NRC staff met with representatives of PG8E on April 10, 1997, to discuss an alternate steam generator tube repair method that involves locked tube support plates that the licensee is interested in proposing.,

Enclosure 1

contains the list of attendees at the meeting.

Enclosure 2 contains the handouts used by the licensee in their presentation.

The staff informed the licensee that we would take this proposal under review.

The staff indicated that its technical review would be detailed and in addition to the materials engineering issues would include risk issues associated with severe accident considerations.

The staff indicated that the licensee should expect the review, process to be lengthy because of the unique and generic nature of the proposal.

The conclusions of the staff review will also be reviewed by the CRGR, which is the normal staff process for generic approvals.

The staff also indicated that there are a number of uncertainties that will have to,be addressed during this review and the outcome of this review is not certain.

Docket Nos.

50-275 and 50-323 Attachments:

1.

List of Attendees 2.

Handout cc w/atts:

See next page 0;:0041 ORIGINAL SIGNED BY Steven D. Bloom, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation I

DISTRIBUTION: (Hard Copy)

Docket File PDIV-2 Reading PUBLIC OGC ACRS

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON> D.C. 20555-0001 May 1, 1997 LICENSEE:

Pacific Gas and Electric Company FACILITY:

Diablo Canyon Nuclear Power Plant

SUMMARY

OF MEETING HELD ON APRIL 10,

1997, WITH PACIFIC GAS EE ELECTRIC (PGLE)

TO DISCUSS MODEL 51 STEAM GENERATOR LOCKED TUBE SUPPORT PLATES The NRC staff met with representatives of PG8E on April 10, 1997, to discuss an alternate steam generator tube repair method that involves locked tube support plates that the licensee is interested in proposing.

Enclosure 1

contains the list of attendees at the meeting.

Enclosure 2 contains the handouts used by the licensee in their presentation.

~The staff informed the licensee that we would take this proposal under review.

The staff indicated that its technical review would be detailed and in addition to the materials engineering issues would include risk issues associated with severe accident considerations.

The staff indicated that the licensee should expect the review process to be lengthy because of the unique and generic nature of the proposal.

The conclusions of the staff review will also be reviewed by the CRGR, which is the normal staff process for generic approvals.

The staff also indicated that there are a number of uncertainties that will have to be addressed during this review and the outcome of this review is not certain.

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

50-275 and 50-323 Attachments:

1.

List of Attendees 2.

Handout cc w/atts See next page

CC:

NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission.

P. 0.

Box 369 Avila Beach, California 93424 Dr. Richard Ferguson, Energy Chair Sierra Club California 1100 11th Street, Suite 311 Sacramento, California 95814 Ms. Nancy Culver San Luis Obispo Mothers for Peace P. 0.

Box 164 Pismo Beach, California 93448 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo, California 93408 Mr. Truman Burns Mr. Robert Kinosian California Public Utilities Commission 505 Van Ness, Room 4102 San Francisco, California 94102 Mr. Steve Hsu Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento, California 94232 Diablo Canyon Independent Safety Committee ATTN:

Robert R. Wellington, Esq.

Legal Counsel 857 Cass Street, Suite D

Monterey, California '3940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower

& Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Christopher J.

Warner, Esq.

Pacific Gas

& Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. Robert P.

Powers Vice President and Plant Manager Diablo Canyon Nuclear Power Plant P. 0.

Box 56 Avila Beach, California 93424 Telegram-Tribune ATTN:

Managing Editor 1321 Johnson Avenue P.O.

Box 112 San Luis Obispo, California 93406 Mr. Gregory M. Rueger Pacific Gas and Electric Company NPG Mail Code AlOD P.O.

Box 770000 San Francisco, California 94177

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Attachment 1

n MEETING WITH PACIFIC GAS AND ELECTRIC STEAM GENERATOR LOCKED TUBE SUPPORT PLATES ATTENDEES A ril 10 1997 PACIFIC GAS

& ELECTRIC COMPANY T. Grebel C. Groff B. Exnor R. Johnson NRC A. Thadani J.

Roe S.

Bloom J. Strosnider E. Sullivan

NRCIPG&E MEETING ON DCPP S TEAM GENERA TORS DCPP MODEL 51 STEAM GENERATORS LOCKED TUBE SUPPORT PLATES STATUS AND PLANS FOR THE FUTURE APRIL 10, $997

OBJECTIVES OF MEETING The objectives of this meeting are:

~ to review the current status of DCPP steam enerators related to denting and locked u e support plates

~ to review the options being considered by PGK for the future

~ to obtain an understanding of the NRC's posi ion concerning tube support plate locking since locked TSPs are a reality of in-service corrosion, is it reasonable to rely on this corrosion for TSP restraint'?

ij-

OUTLINE

~ Background DCpP SG History and Status Degradation predictions

~ Tube Support Plate Efforts To Date WCAP-14707 and Meetings With Staff TSP Degradation Assessment and Inspections

~ Future Plans PWSCC ARC Development

~ Summary and Discussion

BACKGROUND

~ Model 51 Steam Generators Designed in 1960's Operated since mid 1980's

~ MillAnnealed Inconel 600 Tubes

. Carbon Steel 3l4" Tube Support Plates

~ TSP Corrosion Caused Packed CrevicesiDents

~ Denting During First/Second Cycles Staked Condenser Tubes Boric Acid Addition

~ Denting Now Causing ID Cracking - PWSCC

0

'4

Outlet to Steam Line Upper Steam Drum Feedwatertntet ~

U-Tubes (~75'ong)

Anti-Vibration Bars 7H 7C 6H 6C 5H 5C 4H 4C 3H 3C Tube Support Plate (3/4 " drilled plates) 2H 1H 2C, 1C Tube Sheet (21" thick)

WexTex Expansion

~ Manway RCS Outlet (not shown)

RCS Inlet l:,'::WESnnTlNGHOUSE~:MODEtt L'-::.5.l:iSTEnAM:::GENERA'TOR::;::::

t 3:tt>': k" ad

> 'ttnn.,>,n I

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DENTING

~ Denting Has Been Arrested Since Cycle 182 Overall Number Stable Random Samples Have Shown no Change in Dented or Non-Dented Signals

~ Have Seen Cracking in < 1 Volt Dents

~ Cracking is Temperature Driven 60%@1H, 25/o@2H, 9/o@3H, etc.

~ Current Inspection Scope and Technology-Finding Very Small Cracks

~ Population at Risk is Large

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UNIT 1 DENTS Unit1 Dent Distribution (> 5 voltdents)

TSP 1H 2H 3H 4H 5H 6H 7H Total 1-1 1-2 1-3 1-4 2

113 20 391 28 66 4

58 5

67 10 72 2

80 6

96 4

24 39 40 1

2 15 260 168 35 113 364 210 387 207 1281 Total 526 156 107 278 680 2085 Unit 1 Dent Distribution (< 5 volt dents) 1-4 Total TSP 1-1 1-3 1-2 1H 269 908 2087 563 626 1701 770 1529 2H 300 3H 184 239 536 240 335 4H 189 5H 216 378 552 1371 561 1387 252 333 6H 183 241 802 1507 281 653 503 7H 558 Total 1899 663 2377 4882 11959 2289 2889 Note: Vast majority of dents are less than 2 volts.

UNIT2 DENTS Unit 2 Dent Distribution (> 5 volt dents)

TS P 2-1 2-2 2-3 2-4 Total 1H 2H

.3H 4H 0

399 0

10 5

2 1

105 0

0 0

2 3

30 3

7 399 12 40 116 5H 2

1 0

1 6H 0

0 1

1 7H 0

0 Total 8

517 8

43 576 Unit 2 Dent Distribution

< 5 volt dents TSP 1H 2H 3H 4H 5H 6H 225 180 160 186 325 2-2 504 309 216 404 214 2-3 226 132 121 110 157 2-4 Total 381 1336 224 845 277 774 207

. 907 235 931 8

30 7H 26 25 18 41 110 Total 1108 1677 775 1373 4933 Note 1: Vast majority of dents at 1H through 5H are less than 2 volts.

Note 2: Dent population at 6H and 7H does not include dents less than 2 volts. These have not yet been identified.

0

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DENT INDICATIONS FROM ANATEC1R7 BOBBIN REANALYSIS 30 20 PG&E DCPP UNIT1 04/08/97 Steam Generator 1-4 10

!ted Com uter Resources Inc.

BACKGROUND

~ Current Inspection Program 100'ia Bobbin

+ Point: TTS, Dents, R 1 8 2 U Bends Inspecting Over 8000 Dents With + Point in IR8

~ + Point Capability - Increased. Flaw Reporting Over MRPC Easier for Analyst to Identify Cracks

~ + Point Detecting Very Small Cracks From 1R7 Pulled Tube Results - 0.125" L X 23 /0 Dp vG Actual

4 4

C el

UNIT 1 REPAIR STATUS LOCATION Unit 1 Kstodcal Tubes PI ed by Mechanism and Outa e

MECKQ6SM ORIENT 1R7 Total Cumulative EFPYs WPHEXTubesheet Hot Leg TSP (dented)

Hot Leg TSP (nondented)

Cold Leg TSP Rom 1 and 2 U-bend U-bend (Preventive)

Factly Plug PWSCC PWSCC OD

.PWSCC-

~

PWSCC ODSCC Hllmllng PWSCC PWSCC AVBWear Fatigue (88-02)

Probe restriction Circ Circ Circ 2.27 3.45 4.49 5.86 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

4 0

13 2

1 12 5

0 0

1 0

0 7.14 31 10 4

10 1

1 1

1 72 103 3

3 9

16 14 24 0

21 1

5 12 35 0

5 0

2 Total Tubes Plugged 0

0 12 1

29 0

2 117 229 Tubes Unplugged Cum Tubes Plugged Cum Tubes Plugged (%)

1 1

0.01 0.01 0.01 0.10 0.10 0.32 13 14 43 0.82 1.68 1.68

4

UNIT2 REPAIR STATUS Unit 2 Historical Tubes Plu ed b Mechanism and Outa e

LOCATION 2R5 2R6 2R7 5.74 7.08 8.41 ORIENT 2R2 2R3 2R4 2.05 3.16 4.43 1.02 0

0 0

0 0

0 0

0 0

PWSCC PWSCC 24 11 34 1

1 8

1 0

0

%KCIEXTubesheet Circ OD Vol Hot Leg TSP (dented)

PWSCC 0

0 0

0 0

0 17 3

50 0

0 16 Circ PWSCC Axial/Circ PWSCC 0

0 3

0 0

0 PWSCC/ODSCC ODSCC 0

0 0

0 0

0 0

0 4

3 8

69 Hot TSP (nondented)

Cold TSP 5

10 10 0

0 0

~m 1 and 2 U-bend PWSCC 6

0 0

0 0

0 0

0 0

10 2

32 0

0 3

1 3

2 PWSCC Circ AVBWear Fatigue (8842)

U-bend (Preventive) 0 0

0 5

0 0

U-bend (Precautionary)

Rrnv 1 U-bend-8842 0

0 0

0 0

0 0

0 0

19 0

0 Mech damage Probe restriction 0

0 1

0 1

62 38 231 31 0

1 Total Tubes Plugged Tubes Un 1

ed-Cum. Tubes Plu ed Cum. Tubes Plu ed (%)

0 0

0

-19 33 14 15 0.24 0.10 0.11 76 114 345 0.56 0.84 2.54 0.01 Total 8.41 69 10 70 16 80 50 19 365

-20 345 2.54

I

~

~

~

~

~

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I o.

E

REVIEWOF WCAP-14707

~ Joint Project With TVA, PSE8 G and EPRI

~

oncept Reviewed With Staff February 1996

~ WCAP-14707 Produced During 1996 - Submitted y

8E in October 1996 for Use in Structural Integrity Assessment

~ Reviewed With Staff in November 1996 Meetin

~ WCAP-14707 is a Topical Report Which ompares the Forces Tending to Displace TSPs uring a Steam Line Break (SLB) Event With the orces Locking the TSPs Due to Corrosion of the TSPs

4 i4 P

I'

REV/EW OF WCAP 14707

~ Actual Pull Force Tests From a Retired French Steam Generator (Non-Dented Tubes) Are Used to Establish Locking Force - Corroborated by US Plant Experience and Lab Tests Lower 90'lo Confidence Pull Force is 1635 Ibs per TSP Intersection at NOT

~ Dynamic Structural Analyses Performed to Determine Forces Acting to Displace the TSPs during a SLB 60 Ibs per Intersection Maximum for SLB Upstream of SG Flow Restrictor 31 Ibs per Intersection Maximum for SLB Downstream of SG Flow Restrictor (Dose)

It t

REVIEW-OF WCAP 14707

/

~ Leakage From Cracks Within Dented or Pac e TSP Crevices is Shown as Negligible

<0.004 gpm for Through Wall Hole in Tube

~ Effect of Chemical Cleaning also Addresse Locking Force Reduced by a Factor of Approximately 2

~ A More Detailed Finite Element Analysis has Been Completed to Calculate the Tube/TSP and TSP/Wedge Interaction Forces Due to Hot (NO

)

to Cold Temperature Changes This Willbe Submitted to the NRC by Revision of WCAP 14707 Section 10

n

REVIEWOF WCAP 14707

~ Revised Section 10 Concludes:

A limited Number of Tubes Near the Wedge Locations May Exceed Breakaway Force During Cooldown High Fatigue Usage May Occur in Some TSP Wedge Region Locations After Significant Operating Time - These TSP Areas Should be Inspected High Fatigue Usage in The Wedge Welds May Cause Weld Cracking - This Will Not Impact the TSP Support or Restraint Functions

SUMMARY

OF WCAI 14707

~ SLB Forces Acting on the TSPs are Much Smaller Than the Forces Required to Displace the TSP With Packed TSP Crevices

~ 0.1 to 1.3 Tubes With Packed Crevices Within Tube Groups of 13 to 35 Tubes are Adequate to Prevent SLB TSP Displacement (Break Upstream of Flow Restrictor)

~

0.2 to 2:5 Tubes per Group are Adequate to Prevent TSP Displacement Even Following Chemical Cleaning

DCPP TSP CONDITION

~ DCPP has Evaluated TSP Ligament Eddy Current Bobbin Data and Has Concluded There is Not Widespread Degradation:

Unit 2 has 126 Suspect Ligament Calls (SLC)

Unit 1 has 241 SLCs

~ Unit 1 SLCs (Unit 1 1R8 Outage Starts 4/19/97):

About 70% Apparent in PSI Data About 30% Developed Over First Few Cycles Random Pattern - Some Near Wedges an Patch Plates

DCPP TSP CONDITION

~ During 1R8 Outage:

Inspect AllWith + Point Visual Inspection to Clarify All Conditions Resolved Prior to Startup

~ Provide Results to NEI/EPRI Industry Program

g \\!

THE FUTURE - PWSCC ARC

~ PWSCC at Dented TSP Intersections Maintains Flow Margins Limits Repair impact/Man Rem

~ InitialApproach for Axial Cracks Inside TSP Increases Mean Survival Time of Tube b about 5 EFPY - For Cracks Inside TSP

~ ARC Builds on Two Concepts:

TSP Restraint as Discussed in WCAP-14707 Crack Sizing Technique Qualification a

Based on 3 DCPP Pulled Tubes and 13 Lab Cracks

1 ky

PMfSCC ARC a

Completed Performance Demonstration Report and EPRI Appendix H Peer Review (Blind NDE Analysis) a Uncertainty: Length = 0.1",

Average Depth =- 7'/o

~ Must Develop Leak Correlations, Topical Report, etc.

~ 2R8 Implementation is Desired (February 1998)

~ WillAllowFurther Growth Rate Determination

~ Future - Could be Expanded to Address Cracks Extending Outside TSP Based on Structural Integrity and Total Leakage

'~~ v

OTHER PWSCC INITIATIVES,

~ Zinc Addition Planning in Progress for Last 9 Months of Unit 1 Cycle 9 - Start in March 1998 Unit 2 to Follow

~ Sleeving Laser Welded Sleeving Direct Laser Tube Repair Full 0.030" Electro Sleeve Thin Walled 0.008" Electro Sleeve

'I,~

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~At 1/

SUMMARY

~ PG8 E Continues to Believe That Steam Generator Degradation can be Managed Through a Pro-Active Mix of Specific Initiatives

~ Limited TSP Displacement is a Key Building Block in Some of These Initiatives

~ PG8 E Requests NRC Management Feedback on the Feasibility of WCAP-14707 and The Concept That Dented, Packed TSP Crevices will Prevent TSP Movement During a SLB Event