ML20205M254

Summary of 870305 Meeting W/Util in Bethesda,Md Re Steam Generator Leakage problems.Primary-to-secondary Leakage Increased to 0.1 Gpm on 870124 & Then to 0.15 Gpm.Unit Shut Down on 870129.List of Attendees & Util Presentation Encl

ML20205M254
Person / Time
Site:	Millstone
Issue date:	03/18/1987
From:	Jaffe D Office of Nuclear Reactor Regulation
To:	Thadani A Office of Nuclear Reactor Regulation
References
NUDOCS 8704020317
Download: ML20205M254 (50)

Text

,

March 18,1987 4, -

s l

Docket No. 50-336 i

l l

MEMORANDUM FOR:

Ashok C. Thadani, Director l

PWR Project Directorate #8 l

Division of PWR Licensing-B FROM:

D. h. Jaffe, Project Manager i

PWR Project Directorate #8 j

Division of PWR Licensing-B

SUMMARY

OF MEETING HELD WITH NORTNEAST NUCLEAR ENERGYCOMPANY(NNECo)CONCERNINGMILLSTONE UNIT 2 STEAM GENERATOR LEAKAGE On March 5, 1987, representatives of NNECo and the NRC staff met in roem P-422 of the Phillips Building in Bethesda, Maryalnd. A list of attendees is contained in Enclosure 1.

The purpose of the meeting was to describe recent steam generator leakage problems, the subsequent outage, and return to power operation. The presentation made by NNECo is sunnarized in Enclosure 2.

As indicated by NNEco, following the recent refueling outage startup on December 19, 1987, primary-to-secondary leakage increased suddenly to.1 gpm on January 24, 1987 and then to.15 gpm. The plant was shut down on January 29, 1987, prior to reaching a primary-to-secondary leakage rate of.2 gpm.

The licensee identified twc unrelated steam generator problems:

o Misinterpretation of Data - ECT data from the recent refueling outage was re-reviewed and an indication was identified which should have resulted in the tube being plugged. The indication contained a 94% through-wall flaw. The cause of the misinterpretation was associated with incorrect identification of prnbe extent.

o Leaking Tube - A leaking tube was identified which had the equivalent of a 130' through-wall crack.

0704020317 070310 PDR ADOCK 05000336 6

PDH

r 3

i 4

2-As a result of the leaking tube and re-review of the 1986.ECT data, a total of 81 tubes were plugged.

The licensee stated that they would propose to lower the primary-to-secondary leakage rate limit in the Technical Specifica-tion to.15 gpm and also give special attention to those tubes which were characterized as similar to the leaking tube.

NNEco also presented their views on the continued structural acceptability of the steam generator tubes.

N D. H. Jaffe, Project Manager Project Directorate #8 Division of PWR '.icensing-B

Enclosures:

As stated P00#.8 PDD#f )/

PDD#8 P routzer DJaf f tilj/

Acihadant 3

/87 3/j 87 '

3/g/87 j

4 j

e m..

i MEETING

SUMMARY

DISTRIBUTION PWR PROJECT DIRECTORATE #8 Dociet.F11e NRC POR L POR P80#8 Rdg PKreutzer OGC EJordan 8 Grimes ACRS-10 i

NRC Participants 0Jaffe C.Y. Cheng LMarsh EMurphy J.R. Rajan AThadani I

l l

l l

1

t G

l LIST OF ATTENDEES NNECo NRC M.F. Ahern C.Y. Cheng J.M. Benson D.H. Jaffe.

J.A. Blaisdell L. Marsh R.T. Blanchard, Jr.

E. Murphy F.R. Dacimo J.R. Rajan J.F. Ely A. Thadani J.M. Fackelmann W.E. Hutchins E.P Perkins

L o

NORTEAST NUCLEAR ENERGY COMPANY 4

i MILLSTONE UNIT NO 2

DOCKET #50-336 4

4 i

l l

1 l

1 MARCH 5, 1987 MEETING i

j WITH NRC STAFF 4

i i

i FEBRUARY, 1987 STEAM GENERATOR OUTAGE r

I 1

l

O MEETING AGENDA i

l MILLSTONE UNIT N0. 2 - FEBRUARY, 1987 SG OUTAGE o

INTRODUCTION E. P. (CHIP) PERKINS -

LICENSING l

0 REVIEW 0F ECT DATA JAMES M. BENSON - NUCLEAR FROM 1986 REFUELING MATERIALS & CHEMISTRY OUTAGE o

REVIEW 0F ECT DATA JAMES M. BENSON - NUCLEAR FROM FEBRUARY, 1987 MATERIALS & CHEMISTRY OUTAGE o

SG TUBE STRUCTURAL MICHAEL F. AHERN -

CONSIDERATIONS GENERATION MECHANICAL ENGINEERING o

NATURE AND SIGNIFICANCE JOSEPH M. FACKELMANN -

0F THE LEAKING DEFECT NUCLEAR MATERIALS & CHEMISTRY o

SUMMARY

AND CONCLUSIONS E. P. (CHIP) PERKINS -

LICENSING l

4 0

.h a PURPOSE OF MFETING o

DESCRIBE THE EVENTS LEADING TO FEBRUARY, 1987 SHUTDOWN o

REPORT THE RESULTS OF:

- REVIEW 0F 1986 ECT DATA

- FEBRUARY, 1987 OUTAGE ECT DATA o

DETAll CORRECTIVE ACTIONS TAKEN o

DEMONSTRATE THE NNECO CONCLUSION THAT MILLSTON UNIT NO. 2 SG TUBE INTEGRITY IS ASSURED FOR OPERATION THROUGH THE END OF CYCLE 8, l

l i

t

0 1

1-EVENTS LEADING TO SHUTDOWN o-RETURN TO OPERATION FROM REFUELING o-PRIMARY TO SECONDARY RCS LEAKAGE IDENTIFIED o

RCS LEAKAGE INCREASED l

.o REVIEW 0F ECT DATA FROM 1986 REFUELING 4

o MANAGEMENT DECISION TO SHUTDOWN i

a

/

{

'l

4 0 ~

REVIEW 0F ECT DATA 1986 REFUELING OUTAGE JAMES M. BENSON w

4

SUMMARY

OF 1986 MILLSTONE 2 ECT INSPECTION PROGRAM 0

WORK SCOPE 32,000 TUBE ENDS TESTED TO FIRST SUPPORT 2,400 TUBES TESTS FULL LENGTH WORK COMPLETED IN APPR0XIMATELY 14 DAYS 0

DATA ANALYSTS 30 ANALYSTS WERE USED 8 HOURS PER SHIFT CERTIFIED LEVEL llA OR LEVEL 111 O

DATA ANALYSIS TRAINING DURATION:

TWO DAYS DESCRIPTION OF STEAM GENERATOR DESIGN DISCUSSION OF PLANT HISTORY APPLICATION OF SUPPRESSION TECHNIQUES I

4 SEQUENCE OF EVENTS FOLLOWING A TUBE INSPECTION 1

DATA TAPE WAS REVIEWED INDEPENDENTLY BY TWO DATA ANALYSTS.

1 ONE ANALYST WAS DESIGNATED THE " PRIMARY" ANALYST.

THE OTHER ANALYST WAS DESIGNATED THE " SECONDARY" ANALYST.

2 THE RESULTS OF THE PRIMARY AND SECONDARY ANALYST WERE 1

COMPARED.

3 IF NO ADDITIONAL ANALYSIS WAS REQUIRED, THE PRIMARY ANALYSIS RESULT WAS CONSIDERED THE " FINAL" RESULT.

4 A LEVEL 111 WAS REQUIRED T0 REVIEW THE DATA TAPE nND MAKE THE

" FINAL" CALL IF:

EITHER THE PRIMARY OR SECONDARY ANALYST IDENTIFIED A REPAIRABLE INDICATION (140 PERCENT THROUGHWALL).

4 6

SUMMARY

OF ECT DATA REANALYSIS RESULTS FOR TUBES ADJACENT TO TIE RODS 0

- AFTER IDENTIFYING A PRIMARY-TO-SECONDARY LEAK IN THE STEAM GENERATORS, A DATA REVIEW 0F THE 38 UNPLUGGED TUBES ADJACENT TO TIE RODS WAS BEGUN TO ATTEMPT TO IDENTIFY THE LEAKING TUBE.

LARGE TTS DENTS MAKE THESE TUBES SUSCEPTIBLE TO SCC.

A PRIOR TUBE LEAK (1983) WAS LOCATED IN THIS REGION.

O THE REVIEW 0F THE NOVEMBER 1986 ECT DATA TAPES IDENTIFIED DISCREPANCIES FOR TWO 0F THE 76 TUBE ENDS:

SG 1 (CL) L136 - R42 SG 2 (HL) L48 - R94 THE LEAKING TUBE WAS NOT IDENTIFIED IN THIS REVIEW.

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. DESCRIPTION OF DISCREPANCY SG 2 (HL) L48-R94 0

-1987 ANALYSIS OF 1986 DATA FIRST TEST:

PROBE RESTRICTED AT TTS.

SECOND TEST:

94 PERCENT THROUGHWALL FLAW AT HTS +0 2".

0 1986 ANALYSIS OF 1986 DATA FIRST TEST:

PRIMARY:

EXTENT = HTS (TESTED THROUGH HTS TO H1).

SECONDARY:

EXTENT = HTE'(TESTED THROUGH HTE TO HTS).

SECOND TEST:

ANALYSIS AT H1 ONLY:

NO FLAW IDENTIFIED.

O REASON FOR NOT IDENTIFYING FLAW DATA ANALYSIS FOR SECTION OF TUBE BETWEEN HTS AND H1 WAS NOT PERFORMED.

t PRIMARY ANALYST (CONTROLLING ANALYST) INCORRECTLY IDENTIFIED EXTENT OF TEST AS " HTS", INSTEAD OF "HTE'.

DATA ANALYSIS OF RETEST WAS PERFORMED ONLY AT Hl.

4 CRITERIA FOR IDENTIFYING EXTENT OF TEST (1986 REFUELING OUTAGE) 0 EXTENT:

LAST SUPPORT WHICH PROBE PASSES THROUGH O

IF PROBE BECOMES RESTRICTED:

RETEST TO DESIRED EXTENT WITH A SMALLER DIAMETER PROBE.

ANALYZE DATA FROM THAT PORTION OF THE TUBE WHICH WAS NOT TESTED IN THE PREVIOUS TEST.

ns

- /

ll l-2 C2 H2 m.

B B1 i l

l, -2 Cl HTS' CTS HTE

\\

CTE EXTENT = H1 l

EXTENT = HTS

'"" EXTENT = HTE A

~.-

> SUBSEQUENT ACTIONS 0

IDENTIFY ALL TUBES WITH " HTS" EXTENT DESIGNATION:

1800 TUBES IDENTIFIED.

O VERIFY THAT ALL 1800 TUBES WERE TESTED TO H1:

1796/1800 WERE TESTED (AND THEREFORE ANALYZED) T0 "H1".

FOUR TUBES RESTRICTED AT " HTS":

o DATA REVIEW OF RETESTS SHOWED NO FLAWS.

SUMMARY

0 ANALYST ERROR IN DESIGNATING REGION OF TUBE TESTED LED TO MISS OF ONE DEFECT CALL.

O REVIEW 0F ALL POTENTIAL SIMILAR MISSES SHOWED NO ADDITIONAL DEFECTS.

. DESCRIPTION OF DISCREPANCY SG 1 (CL) L136 - R42 o

1987 ANALYSIS OF 1986 DATA 83 PERCENT THROUGHWALL FLAW AT CTS +2 9".

PIT CHARACTERISTICS.

DENT EXTENDS FROM CTS TO CTS +3 0".

0 1986 ANALYSIS OF 1986 DATA 4

PRIMARY:

90 PERCENT THROUGHWALL FLAW.

SECONDARY:

90 PERCENT THROUGHWALL FLAW.

FINAL (LEVEL 111):

NO FLAW IN TUBE.

0 POSSIBLE REASON FOR INCORRECT CALL COMBINATION SIGNAL OF DENT AND FLAW WAS MISINTERPRETED AS COPPER.

o DENTS ARE NOT EXPECTED 3" AB0VE TUBESHEET.

o A COPPER MIX WAS AVAILABLE BUT NOT USED.

. SUBSEQUENT ACTIONS 0

REVIEW 1986 ECT DATA TAPES FOR TUBES MOST LIKELY TO HAVE LARGE DENTS EXTENDING AB0VE TUBESHEET.

DATA REVIEWED FOR 12 TUBES WHICH RESTRICTED SLEEVES.

o NO DENTS EXTENDED MORE THAN 2".

o NO COMBINATION OF DENT / FLAW SIGNALS.

DATA ~ REVIEWED FOR 18 TUBES WHICH RESTRICTED ECT PROBE AT TOP 0F TUBESHEET.

o NO FLAW IDENTIFIED.

O REVIEW 1986 ECT DATA TAPES FOR A SAMPLE OF APPROXIMATELY 50

" DEFECT RESOLUTIONS" MADE BY THE LEVEL 111 ANALYST (ANALYST X) WHO MADE THE INCORRECT CALL ON L136-R42 ADDITIONAL TUBES IDENTIFIED WHICH REQUIRED REPAIR.

O REVIEW ALL DEFECT RESOLUTIONS BY ANALYST X.

O REVIEW A SAMPLE OF DEFECT RESOLUTIONS BY THE OTHER LEVEL 111 REVIEWERS.

INCLUDE ALL DOUBLE REVERSALS (140 PERCENT PRIMARY AND SECONDARY, <40 PERCENT FINAL).

INCLUDE A SAMPLE OF SINGLE REVERSALS (140 PERCENT PRIMARY OR SECONDARY, <40 PERCENT FINAL).

. MILLSTONE 2 FEBRUARY 1987 ECT DATA REVIEW

SUMMARY

ANALYST X FEB.'87 REVIEW

1. REVIEWED

1. ANALYZED

1. 140 PERCENT CRITERIA NOV '86 FEB '87 FEB '87 140% PRI AND SEC 88 88 22

<40% FINAL '86 140% PRI OR'SEC 172 172 14

<40% FINAL '86 TOTAL 260 260 36 OTHER ANALYSTS FEB '87 REVIEW

1. REVIEWED

1. ANALYZED

1. 140 PERCENT CRITERIA NOV '86 FEB '87 FEB '87 140% PRI AND SEC 28 28 0

<40% FINAL '86 140% PRI OR SEC 507 196 0

<40% FINAL '86 TOTAL 536 224 0

i

s

SUMMARY

OF 140 PERCENT THROUGHWALL FLAWS IDENTIFIED BY FEBRUARY 1987 DATA REVIEW 0

ALL 36 0F THE NOVEMBER 1986 DEFECT RESOLUTIONS, DETERMINED TO BE 140 PERCENT THROUGHWALL BY THE FEBRUARY 1987 REVIEW, WERE MADE BY ONE ANALYST.

O IN 14 0F THE 36 CASES, A LEVEL 11 DATA ANALYST ALSO CONCLUDED THAT N0 140 PERCENT THROUGHWALL FLAWS WERE PRESENT.

SIGNALS NOT EASY T0 INTERPRET.

O IN 13 0F THE 36 CASES, THE FEBRUARY 1987 REVIEW CHANGED THE NOVEMBER 1986 ESTIMATED FLAW DEPTH BY 110 PERCENT.

WITHIN ECT MEASUREMENT ACCURACY.

O IN 31 0F THE 36 CASES, THE FEBRUARY 1987 REVIEW ESTIMATED FLAW DEPTHS OF BETWEEN 40 PERCENT AND 48 PERCENT.

WITHIN 8 PERCENT OF THE MILLSTONE 2 REPAIR CRITERIA.

SUMMARY

0 REVIEW BOUNDED UNIQUE DENT INTERFERENCE FOR SMALL VOLUME FLAWS.

O REVIEW BOUNDED ALL OF ANALYST X REVERSALS.

IN 86 PERCENT OF THE CASES, ANALYST X WAS CORRECT IN DISPOSIT10NING DEFECTS INCORRECTLY CALLED BY THE LEVEL II ANALYSTS.

FOR 34 0F THE 36 FEBRUARY 1987 >40 PERCENT CALLS, ANALYST X l

EITHER:

o WAS WITHIN ECT MEASUREMENT ACCURACY (110 PERCENT) 0F THE 1987 CALL.

o DISPOSITIONED FLAWS WITHIN 8 PERCENT OF THE REPAIR LIMIT.

o WAS IN AGREEMENT WITH ONE OF THE LEVEL II ANALYSTS.

O REVIEW 0F 40 PERCENT OF THE OTHER ANALYSTS' REVERSALS SHOWED N0 INCORRECT CALLS.

l

. CORRECTIVE ACTIONS UNDER CONSIDERATION 0

EVALUATE THE METHOD USED TO REPORT THE EXTENT OF TEST.

O CONSIDER COMPARING EXTENT OF TESTS REPORTED BY PRIMARY AND SECONDARY ANALYST, AND RESOLVING ANY DISCREPANCIES.

0 EVALUATE THE PRACTICE OF LEVEL 111 ANALYST CHANGING PRIMARY AND/0R SECONDARY DEFECT CALLS.

O CONSlrcR DGuuMENTING REASON FOR DEFECT' REVERSALS.

O REVIEW AL. ' ",/ OF PLANT SPECIFIC ANALYSIS TRAINING AND QUALIFICATION N

4 ~

REVIEW 0F ECT DATA FEBRUARY, 1987 OUTAGE JAMES M. BENSON

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O e FEBRUARY 1987 REVIEW 0F PREVIOUS ECT DATA TAPES SG 1 (HL) L25 - R19 0

1985 ECT INSPECTION APPROXIMATELY 30 PERCENT THROUGHWALL FLAW OD INITIATED SIGNAL AMPLITUDE 1 7 VOLTS NEAR TOP OF TUBESHEET 1

0 1986 ECT INSPECTION APPROXIMATELY 30 PERCENT THROUGHWALL FLAW OD INITIATED SIGNAL AMPLITUDE 1.6 VOLTS NEAR TOP OF TUBESHEET DENT AT TOP OF TUBESHEET EXTENDS INTO FLAW ESSENTIALLY NO CHANGE IN SIGNAL FROM 1985 REFUELING OUTAGE TO 1986 REFUELING OUTAGE.

,22-1987 ECT INSPECTION

SUMMARY

0 B0BBIN PROBE LEAKER o

FLAW IDENTIFIED AT HTS +0 0."

o SIGNAL AMPLITUDE 7.8 VOLTS.

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o AXIAL EXTENT OF FLAW LESS THAN 0 2".

o ECT SIGNAL CHANGED SIGNIFICANTLY FROM NOVEMBER 1986 TO FEBRUARY 1987 21 TUBES SURROUNDING LEAKE.R 4

o SIGNALS UNCHANGED DECEMBER 1986 TO FEBRUARY 1987 o

NO SIGNALS SIMILAR TO 1987-TEST OF LEAKING TUBE.

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. MILLSTONE 2 STEAM GENERATOR TUBE PLUGGING

SUMMARY

(FEBRUARY 1987 OUTAGE)

REASON SG 1 SG 2 LEAKING TUBE 1

TUBES SURROUNDING LEAKER 6

TUBES ADJACENT TO TIE RODS 25 13

>40 PERCENT FLAWS, BASED ON REVIEW 29 7

0F 1986 ECT DATA TAPES TOTAL 61 20 1

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4 6.

STEAM GENERATOR TUBE STRUCTURAL CONSIDERATIONS MICHAEL F. AHERN

. MILLSTONE UNIT NO. 2 STEAM GENERATOR TUBE INTEGRITY l

OVERVIEW l

o ALL OF THE TUBES WHICH HAD DEFECTS IN EXCESS OF THE TECHNICAL SPECIFICATION ALLOWABLE WERE PLUGGED.

o SOME ADDITIONAL TUBES WERE PLUGGED TO IMPROVE THE UNIT'S RELIABILITY.

o THE LEAKING TUBE WAS FOUND TO HAVE A CIRCUMFERENTI AL INDICA-TION.

o SINCE THIS WAS THE FIRST SUCH INDICATION DISCOVERED AT MILLSTONE UNIT 2, TUBE STRUCTURAL INTEGRITY MEASURES WERE REVIEWED.

o BASED ON THIS REVIEW, THE TUBES SURROUNDING THE LEAKER WERE STABILIZED AND PLUGGED.

1 o

IN ADDITION, THE PRIMARY TO SECONDARY LEAKAGE LIMIT WAS REDUCED FROM 0 5 GPM TO 0 15 GPM PER STEAM GENERATOR.

l o

THE CORRECTIVE ACTIONS TAKEN ENSURE TUBE INTEGRITY FOR OPERA-TION THROUGHOUT THE CURRENT FUEL CYCLE.

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. MILLSTONE UNIT NO. 2 STEAM GENERATOR TUBE INTEGRITY TUBE PLUGGING d

o FOLLOWING THE EDDY CURRENT TEST DATA REVIEW, TUBES WITH DEFECTS IN EXCESS OF 40% THROUGH WALL WERE PLUGGED.

o THE PLUGS USED WERE OF THE SAME MECHANICAL DESIGN WHICH HAS PREVIOUSLY BEEN INSTALLED AT MILLSTONE UNIT 2 j

o A TOTAL OF 81 TUBES WERE PLUGGED.

39 HAD DEFECTS IN EXCESS OF 40% THROUGH WALL 36 WERE PLUGGED TO IMPROVE RELIABILITY t

6 WERE STABILIZED AND PLUGGED o

THE SAFETY ANALYSIS BASED PLUGGING LIMITS WERE REVIEWED AND REMAIN VALID.

. MILLSTONE UNIT NO. 2 STEAM GENERATOR TUBE INTEGRITY TUBE PLUGGING o

A TOTAL OF 36 TUBES WERE PLUGGED TO IMPROVE THE UNIT'S RELIABILITY.

o ALL OF THE TUBES SURROUNDING EGG-CRATE TIE RODS HAVE NOW BEEN REMOVED FROM SERVICE.

o THESE TUBES HAVE BEEN CONSIDERED TO BE MORE SUSCEPTIBLE TO STRESS CORROSION THAN.THE AVERAGE TUBE.

IT MAY BE CAUSED BY A THERMAL EXPANSION MISMATCH WITH THE TIE R0D ONCE THE' TWO STRUCTURES BECOME COUPLED BY EGG-CRATE DENTING.

THE RESULT-ING TUBE KINKING COULD GIVE RISE TO PLASTIC STRAINS AND ALLOW STRESS CORROSION CRACKING.

o BECAUSE ONLY 36 REMAINED, ALL 0F THEM WERE PLUGGED.

o THIS ACTION WILL REDUCE THE PROBABILITY OF FUTURE FORCED OUTAGES.

1 1

1

. MILLSTONE UNIT NO. 2 STEAM GENERATOR TUBE INTEGRITY LEAKING TUBE o

THE TUBE LEAK WAS FOUND IN LINE 25,. R0W 19 0F THE STEAM GENERATOR #1, HOT LEG.

o THE DEFECT INDICATION IS CIRCUMFERENTIALLY ORIENTED OVER A 225 DEGREE ARC. IT HAS A MAXIMUM VOLUME OF METAL LOSS OVER A 40 DEGREE ARC.

IT IS LOCATED AT THE TOP 0F THE TUBESHEET.

o THE LEAK RATE AT NORMAL OPERATING CONDITIONS WAS 0 15 GPM.

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, - - MILLSTONE UNIT N0. 2 STEAM GENERATOR TUBE INTEGRITY STRUCTURAL IMPLICATIONS OF THE LEAKING TUBE i

o SINCE THROUGH WALL CIRCUMFERENTIAL DEFECTS ARE NEW TO MILLSTONE 2,

TUBE STRUCTURAL INTEGRITY MEASURES WERE REVIEWED.

o BECAUSE SUCH DEFECTS COULD SEVER A TUBE AND POTENTIALLY RESULT IN TUBE TO TUBE CONTACT, SURROUNDING TUBES WERE STABILIZED AND PLUGGED.

o THE STABILIZERS PREVENT FURTHER TUBE TO TUBE CONTACT IF A SURROUNDING TUBE SHOULD BECOME SEVERED.

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MILLSTONE UNIT N0.-2 STEAM GENERAT'R TUBE INTEGRITY O

s STRUCTURAL IMPLICATIONS OF THE LEAKING' TUBE ALTHOUGHTHELEAKINGTUBEHASBEENPLUGGEDAND[P'OTENTIALWEAR o

CONCERNS MITIGATED, ADDITIONAL DEFECTS OF THIS NATURE WERE' POSTULATED.

STRUCTURAL IMPLICATIONS OF SUCH DEFECTS WERE THEN CONSIDERED.

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FRACTURE AND PLASTICITY CALCULATIONS WERE PERFORMED.

IT WAS ESTIMATED THAT THE DEFECT IN THE LEAKING TUBE IS STRUCTURALLY EQUIVALENT TO A 130 DEGREE THROUGH WALL CRACK.

o THE MARGIN OF SAFETY AGAINST BURST FOR A 130 DEGREE THROUGH WALL DEFECT WAS FOUND T0. BE 14 FOR ACCIDENT CONDITIONS (INCLUDING DYNAMIC EFFECTS) AND OVER 3 FOR NORMAL CONDITIONS.

o THESE MARGINS MEET THE REQUIREMENTS OF REGULATORY GUIDE 1 121 o

015 GPM HAS BEEN ADOPTED AS THE MAXIMUM ALLOWABLE LEAK RATE PER STEAM GENERATOR AT MILLSTONE 2 FURTHER WORK MAY ALLOW THIS LIMIT TO BE CHANGED.

o IN ADDITION, INCREASED LEAKAGE UNDER ACCIDENT CONDITIONS WAS CONSIDERED.

IT WAS FOUND THAT THE CONSERVATIVELY ESTIMATED MAXIMUM TOTAL LEAK RATE UNDER ACCIDENT CONDITIONS IS 0.75 GPM.

SINCE THIS IS LESS THAN THE 1 0 GPM ASSUMED IN THE ACCIDENT ANALYSES, IT IS ACCEPTABLE.

l MILLSTONE UNIT NO. 2.

' STEAM GENERATOR TUBE INTEGRITY

SUMMARY

o ALL OF THE TUBES WHICH HAD DEFECTS IN EXCESS OF THE TECHNICAL SPECIFICATION ALLOWABLE WERE PLUGGED.

o SOME ADDITIONAL TUBES WERE PLUGGED TO IMPROVE THE UNIT'S RELIABILITY.

o THE LEAKING TUBE HAD A

NEW TYPE OF INDICATION.

THE STRUCTURAL IMPLICATIONS OF THROUGH WALL CIRCUMFERENTIAL DEFECTS WERE CONSIDERED.

o THE TUBES SURROUNDING THE LEAKER WERE STABILIZED AND PLUGGED TO PREVENT POSTULATED WEAR FAILURES.

o THE LEAKING TUBE RETAINED ACCEPTABLE MARGINS AGAINST BURST.

o BY LIMITING PRIMARY-TO-SECONDARY LEAKAGE TO 0 15

GPM, ACCEPTABLE STRUCTURAL MARGINS ARE ASSURED FOR FUTURE DEFECTS OF THIS TYPE.

o WITH THESE MEASURES TAKEN, THE STRUCTURAL INTEGRITY OF THE STEAM GENERATORS IS ENSURED FOR THE BALANCE OF THE CURRENT FUEL CYCLE.

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NATURE AND SIGNIFICANCE OF THE LEAKING DEFECT JOSEPH M. FACKELMANN

. t TRENDS i

1985 - STABLE, SMALL VOLUME,'30 PERCENT FLAW LOCATED ~TTS 4

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1986 - NO CHANGE i

i 1987 - THROUGHWALL LEAK, APPROXIMATELY 0 15 GPM i

LARGE VOLUME DEFECT LOCATED TTS I

DETECTED BY BOBBIN PROBE AND ROTATING PROBE 4

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DEFECT INTERPRETATION 1

0 PROBABLY CIRCUMFERENTIAL CRACK.

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PROBABLY INITIATED FROM BAND OF PITS ON SECONDARY-SIDE.

0' SCC OR FATIGUE BASED ON'HIGH GROWTH RATE.

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. CRAEK MECHANISM 0

STRESS CORROSION CRACKING.

O CORRlDANT SUSPECTS S, Cu, OR UNKNOWN IMPURITY.

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HIGH TEMPERATURE DURING OPERATION.

0 HIGH STRESS DUE T0 " DENTING EFFECTS".

O MILLSTONE 2 TUBING SUSCEPTIBILITY MARGINAL.

i 1983 P/S LEAK, ADJACENT TIE ROD.

SCC CONFIRMED IN 1985 TUBE PULL (HIGH " KINKING" STRESS, CRACK APPROXIMATELY 45 TO VERTICAL).

NO OTHER SCC LEAKS.

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9 ALTERNATE CRACK MECHANISM 0

HIGH CYCLE FATIGUE A POSSIBLE CRACK MECHANISM.

0 CYCLIC STRESS COULD BE PRESENT IF FLOW INDUCED VIBRATION OCCURS.

O FLOW INDUCED VIBRATION COULD OCCUR IF BOTH THE FIRST AND SECOND EGGCRATE SUPPORTS ARE MISSING AND THE TUBE IS IN A HIGH FLUID VELOCITY REGION.

1 0

ISOLATED INCIDENT DUE TO THE LOW PROBABILITY OF MISSING SUPPORTS AT CONSECUTIVE LEVELS, AND THE MODERATE DEGREE OF SUPPORT CORROSION IN THIS REGION.

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MULTIPLE CIRCUMFERENTIAL CRACKING CONSIDERATIONS 0

SMALL POPULATION (161) 0F SUSCEPTIBLE TUBES.

O LONG INITIATION TIME RELATIVE TO THROUGHWALL PROPAGATION.

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0 NONHOMOGENEOUS MATERIAL, STRESS, ENVIRONMENT.

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SCC OCCURRENCE PROBABILITY VERY LOW IN EARLY STAGES.

O LEAK BEFORE BREAK CHARACTERISTIC 0F SCC.

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SIGNIFICANT POPULATION OF DEEP DEFECTS WITHOUT LEAKAGE NOT CREDIBLE.

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. MILLSTONE 2 SECONDARY CHEMISTRY (AVERAGE)

CY 7 (SEPT CY 5 CY 6 CY 7 1986)

CL (PPB) 57 29 23 3

NA (ppa) 28 15 13 3

CATION CONDUCTIVITY 16 11 06 0 16 (UMHOS/CM) i 1

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C CORRECTIVE ACTIONS 0

SECONDARY CHEMISTRY IMPROVEMENTS:

PRESENT MILLSTONE 2 CHEMISTRY IS STATE-0F-THE-ART.

S INTRODUCTION MINIMlZED.

Cu INPUTS MINIMAL AS A RESULTS OF CONDENSER AND FEEDWATER HEATER REPLACEMENT.

ANY IMPURITY CONTAMINATION EXPECTED TO BE HIGHLY LOCAllZED.

O TUBE PULL UNDER CONSIDERATION:

TO ESTABLISH DEFINITE MECHANISM AND MORPHOLOGY OF DEFECT AND OPTIMIZE NDE.

TO BE CONSIDERED DURING NEXT REFUELING OUTAGE.

O NDE OPTIMlZATION:

IMPROVED TECHNIQUES.

IMPROVED DATA ANALYSIS.

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4

.I CONCLUSIONS O

CONTINUED OPERATION OF THE STEAM GENERATOR IS SAFE WITH TIGHTENED LEAKAGE CONTROL.

0 CRACKS ARE GOVERNED BY LEAK BEFORE BREAK.

0 MULTIPLE TUBE CRACKS ARE NOT CREDIBLE.

0 EFFORTS ARE BEING MADE TO FURTHER CHARACTERIZE AND MITIGATE THE EFFECTS OF THE CRACK.

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SUMMARY

AND CONCLUSIONS be E. P. (CHIP) PERXINS i

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SUMMARY

AND CONCLUSIONS o

PROGRAMMATIC QUESTIONS RE: 1986 ECT PROGRAM ADDRESSED

- REVIEW B0UNDED REVERSALS BY LEVEL 111 REVIEWERS

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- REPORTING METHOD PROBLEM ADDRESSED o

81 TUBES WERE PLUGGED (FEBRUARY, 1987 OUTAGE) 1 - LEAklNG TUBE 6 - SURROUNDING (STABILIZED, T00) 36 - ADJACENT TO THE RODS 38 - 2 40 PERCENT ON RE-REVIEW (2 ADJACENT TO TIE RODS)

- ALL TUBES PLUGGED - DEFECTS 2 T.S. LIMITS

- SOME TUBES PLUGGED AS A PRECAUTION o

LEAKING TUBE

- MECHANISM 0F DEGRADATION IS UNCERTAIN

- SURROUNDING TUBES STABILIZED

- LEAKING TUBE RETAINED ACCEPTABLE STRUCTURAL MARGINS 15 GPM LEAK LIMIT ENSURES ACCEPTABLE STRUCTURAL MARGINS FOR OTHER TUBES o

OVERALL

- CRACKS ARE GOVERNED BY " LEAK BEFORE BREAK"

- MULTIPLE TUBE CRACKS ARE NOT LIKELY

- EFFORTS CONTINUING TO FURTHER CHARACTERIZE AND MITIGATE THE EFFECTS OF THE CRACK o

AB0VE-STATED ACTIONS AND MEASURES ENSURES THE STRUCTURAL INTEGRITY OF THE MP2 SGs FOR THE REMAINDER OF CYCLE i