ML20012E821

Summary of 900222 Meeting W/Util in Rockville,Md Re Oct 1989 mid-cycle Steam Generator Tube Insp at Facility.Licensee Indicated That Plans in Place to Replace Steam Generators in 1992.List of Attendees & Viewgraphs Encl

ML20012E821
Person / Time
Site:	Millstone
Issue date:	03/22/1990
From:	Vissing G Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 9004060362
Download: ML20012E821 (80)

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March 22, 1990 p

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Docket flo. 50-336 LICENSEE: Northeast Utilities FACILITY: Millstone, Unit No. 2

SUMMARY

OF itEETING WITH REPRESENTATIVES OF NORTHEAST UTILITIES CONCERNING THE OCTOBER 1989 MID CYCLE STEAM GENERATOR TUBE IliSPECTION AT 111LLSTONE 2, FEBRUARY 22, 1990 INTRODUCTION On February 22, 1990, re?resentatives o" the NRC and Northeast Utilities met in the NRC office in Roc kville, Marylanc to review and discuss the results and the analysis of the results of the October 1990 mid-cycle steam generator tube inspection at Millstone Unit No. 2.

The attendance list is provided in.

A copy of the slide presentation is provided in Enclosure 2.

DISCUSSION The ager.da and presentation was as inJicated in Enclosure 2.

The October 1989 rid-cycle sttem generator tube inspection was performed in response to a concern for the steam ger.erator tube integrity as a result of the number of tet(s that showed circur.ferential cracking at the end of cycle 9 steam eenerator tube inspection. This was not a technical specification inspection but a plarred inspection to determine if the cracking phenomena has been arrested. The scope of the inspection included 7385 tubes inspected to the first support plate by tobbin type coil, 7899 tubes inspected by the rotating pancake coil and 170 tubes inspected by ultrasonic tests. A total of 216 tubes rhewed defects and were plugged. However, with one exception which is still under evaluation (i.e., tubt Ic L45/R13), the defective tubes still satisfied Regulatory Guide 1.121 margins to burst at the time they were plugged.

The eviderce indiceted that caustic is the cause of corrosion and that boric acid cddition to the secondary side appears to have been effective in stopping the corrosion process.

Steam Generator No. I has exhibited more degradation than Steam Generator No.

2.

Two different vendors provided the tubes for steam generators. Tubes of SG1 had higher material properties on the average than tubes of SG2. This accounts for the differences in corrosion susceptibility.

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L 9004060362 900322 PDR ADOCK 05000336 Q

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• 2-March 22, 1990 The licensee predicts a best estimate of the number of cracks which will be identified at the end of cycle 10 refueling outage to be 45. This includes 20 incipient cracks which formed during caustic conditions prior to cycle 9 and propagated during cycle 10 and 25 cracks existing below detectability levels which will become detectable.

The licensee indicated that Millstone 2 stil'i has a margin of 1000 tubes, 200 in SGI and 750 in SG2, before derating will be necessary.

The licensee indicated that plans are in progress to replace the steam generators in 1992.

However, no firm decision has yet been made. The estimated cost of such a project is $160,000,000. They have ordered two replacements from B&W of Canada. Modification such a crane upgrades are in

. progress for preparation of the replacements.

CONCLUSION The staff is reviewing the information presented during the' meeting and will continue to monitor the effectiveness of the licensee's actions to ensure continued safe operation of the Millstone Unit 2 steam generators.

The licensee has indicated that it will submit its evaluation of tube Ic L45/R13 (seeabovediscussion)byJune1,1990, signed by D. Jaffe for Guy S. Vissing, Project Manager Project Directorate I-4 Division of Reactor Projects - I/II

Enclosures:

As stated cc w/ enclosures:

See next page Vv

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.The licensee predicts a best estimate of the number of cracks which will be

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identified at the end of cycle 10 refueling outage to be 45. This includes 20 t

incipient cracks which formed during caustic conditions prior to cycle g and l

propagated during cycle 10 and 25 cracks existing below detectability levels which will become detectable, j

The licensee indicated that Millstone 2 still has a margin of 1000 tubes, 200 in SGI and 750 in SG2, before derating will be necessary.

The licensee indicated that plans are in progress to replace the steam generators in 1992. However, no firm decision has yet been made. The estimated cost of such a project is $180,000,000.. They have ordered two replacements from B&W of Canada. Modification such a crane upgrades are in progress for preparation of the replacements.

CONCLUSION The staff is reviewing the information presented during the meeting and will continue to monitor the effectiveness of the licensee's actions to ensure continued safe operation of the Hillstone Unit 2 steam generators. The licensee has indicated that it will submit its evaluation of tube Ic L45/R13 (see above discussion) by June 1,1990.

4 Guy sing, reject Manager Pro,iect Directorate I-4 Division of Reactor Projects - I/II

Enclosures:

As stattd cc w/ enclosures:

i See next page 1

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DISTRIBUTION FOR MEETING

SUMMARY

DATED:' March 22, 1990

- %&, - _ - __axywxr-4 NRC & Local PDRs-Plant File

'J. Stolz S. Norris-

'G. Vissing L

'0GC E. Jordan-(MNBB 3302)

NRC Participants F. Witt C.Y. Cheng Jack Strosnider (Region 10+)

'c A.Lohmeier(ghorst(RegionI)

Peter J. Jabi i*

RegionI) s L

Lynn Connor Emmett Murphy

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ACRS(10) t pq J. Dyer.(Region I,17G21) k k l

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Mr. Edward J. Mroczka Millstone Nuclear Power Station

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Northeast Nuclear Energy Company Unit No. 2 l

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Gerald Garfield, Esquire R. M. Kacich, Manager Day, Berry and Howard Generation Facilities Licensing rounselors at Law Northeast Utilities Service Company i

City Place Post Office Box 270 Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. O. Nordquist i

Nuclear Operations rinetor of Quality Services i

Northeast Utilities Service Company ttortheast Utilities Service Company j

Post Office Box 270 Post Office Box 270 j

Hartford, Connecticut 06141-0270 Hartford, Connecticut 06141-0270 KeVin liCCarthy, Director Regional Administrator Radiation Control Unit Region I Department of Environmental Protection U. S. Nuclear Regulatory Comission State Office Building 475 Allendale Road Hartford, Connecticut 06106 King of Prussia, Pennsylvania 19406 Bradford S. Chase, Under Secretary First Selectmen Energy Division Town of Waterford Office of Policy and Management Hall of Records i

80 Washington Street 200 Boston Post Road Hartford, Connecticut 06106 Waterford, Connecticut 06385 S. E. Scace, Nuclear Station Director W. J.-Raymond, Resident Inspector i

tillister.e !!uclear Power Station Millstone Nuclear Power Station Ncrtheast Nuclear Energy Company c/o U. S. Nuclear Regulatory Comission Post Office Box 128 Post Office Box 811 Waterford, Connecticut 06385 Hiantic, Connecticut 06357 J. S. Veenan, Nuclear Unit Director Charles Brinkman, Manager lii11 stone Unit flo. 2 Washington Nuclear Operations liortheast Nuclear Energy Company C-E Power Systems Post Office Box 128 Combustion Engineering, Inc.

l Uaterford. Connecticut 06385 12300 Twinbrook Pkwy Suite 330 Rockville, Maryland 20852 i

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ENCLSOURE 1 ATTENDANCE LIST FOR MEETING WITH NORTHEAST UTILITIES i1 CONCERNING L

STEAM GENERATOR TUBE INSTECTION FOR MILLSTONE UNIT NO. 2 February 22, 1990 Guy S. Vissing NRR Project Manager Joe Fackelmayer NU Price. Eng.

Janes Benson NU Engineer Jay Ely NU Supv. Gen. Eng.

W.E. Hutchins NU Senior Licensing Engineer J.S. Keenan NU Director tiillstone Unit 2 Mike Schoppman FP&L Washington Licensing Re).

F.C. Anderson NU Nuclear Materials and Caemistry C.F. Sears NU Vice President K.A. Colgan NU Engineer, Nuc. Mater. & Chem.

H.F. Conrad NRR t'aterials Engineer P.J. Parulis NU Unit 2 Engeneering-Millstone Frart J. Witt NRR Chemical Engineer C.Y. Ct.eng NRR/EMCB Branch Chief i

Jeck Strosnider NRC/ Region I Chief Materials & Processes Sec.

Peter J. Habighorst NRC/ Region I Resident itP-2 R.V. Winters NRC/ Region I Reactor Engineer A. Lohmeier NRC/ Region I Reactor Engineer Lynn Connor The NRC Calendar Consultant Emmett iturphy NRC/EliCB Materials Engineer i

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l NORTNEAST NUCLEAR ENERGY COMPANY HILLSTONE UNIT NO. 2 DOCKET NO. 50-336-j t

FEBRUARY 22, 1990 MEETING WITN

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NRC STAFF

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STEAM GENERATOR EXAMINATION RESULTS l

AND SAFETY ASSESSMENT l

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i AGENDA i

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o INTRODUCTION C. F. SEARS i

o CRACK ASSESSMENT OVERVIEW J. M. FACKELMANN l

o NONDESTRUCTIVE EXAMINATION J. M. BENSON j

o.

TUBE REMOVAL PROGRAM K. A. COLGAN L

.o CORROSION MECHANISM / IMPLICATIONS F. C. ANDERSON l

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OPERATIONAL MONITORING P. J. PARULIS q

o CONCLUSIONS C. F. SEARS 1

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CRACK ASSESSMENT OVERVIEW l

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CRACKING DISCOVERED IN JANUARY 1987 WITH l

0.15 opM LEAK FROM TUBE IN SG1 HOT LEG o

CRACK MECHANISM NOW WELL DEFINED i

CAUSTIC CRACK INITIATION PRIOR TO CYCLE 9 INITIATION ARRESTED l

RATE DIFFERENCE BETWEEN SG1 AND SG2 DUE TO MATERIAL FACTORS o

PITTING AND DENTING UNDER CONTROL l

o 45 CRACKS PROJECTED REMAINDER CYCLE 10 l

l 4/M2SG 02/22/90

3 MILLSTONE 2 STEAM GENERATORS

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t BURST TESTS L

o ADDITIONAL REGULATORY GUIDE STRENGTH MARGIN FROM 1

i AXIAL SEPARATION OF MICR0 CRACKS LIGAMENT MORPHOLOGY TUBESHEET STRENGTHENING k

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o DEGRADATION REMAINDER CYCLE 10 ASSURED WITHIN REGULATORY GUIDE 1.121 LIMITS

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NOT MORE TRAN ONE 77 PERCENT (AVERAGE)

THROUGH-WALL CRACK AT 95 PERCENT CONFIDENCE l

0.1 GPM SHU1DOWN REQUIREMENT (EQUIVALENT OF 100 PERCENT THROUGH-WALL x 350) 1 ADVANCED LEAK HONITORING PROGRAM INCLUDING N-16 MONITOR o

OPERATION FOR THE REMAINDER OF CYCLE 10 FULLY JUSTIFIED LOW PROBABILITY LARGE CRACKS MITIGATING FACTORS ASSOCIATED WITH LARGE CRACKS HIGH PROBABILITY OF LEAK-BEFORE-BREAK 1

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l OCTOBER 1989 MILLSTONE 2 STEAM GENERATOR EXAMINATION SCOPE L

TEST DESCRIPTION NUMBER OF TESTS BOBBIN TO FIRST SUPPORT 7385 ROTATING PANCAKE COIL 7899*

ULTRASONIC TEST 170 i

• INCLUDES A 514 TUBE EXPANSION PROGRAM TO BOUND CRACK REGION.

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PROBE VARIOUS COMBINATIONS OF. MULTIPLE CRACKS WERE DETECTED l

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MIZ-18 INTERFACE PROBLEMS o

ONGOING STUDIES i

COMPARISON OF TRANSMIT-RECEIVE, ROTATING PANCAKE COIL, AND ULTRASONIC DATA DEVELOPMENT OF FREQUENCY MIXES FOR TRANSHIT-RECEIVE PROBE o

POTENTIAL FUTURE APPLICATION PAPID/ RELIABLE DETECTION OF CIRCUMFERENTIAL CRACKS SIMULTANEOUS DETECTION OF CRACK AND NONCRACK FLAWS 10/M2SG 02/22/90

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SURRY OF TUBE PLUGGING OCTOBER 1989 MILLSTONE 2 STEAM GENERATOR EY_ AMINATION REASON FOR STEAM GENERATOR PLENUM

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PLUGGING SG1--CL SG1--HL SG2--CL SG2--HL TOTAL TTS CRACK 36 58 7

3 104 TTS POSSIBLE CRACK 2

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AVERAGE PITTING PROGRESSION (N0V. '86 - OCT. '89) l

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BEST ESTIMATE PROJECTION OF HILLSTONE 2 STE.41 GENERATOR TUBE REPAIRS (PRIMARILY PITTING) l PROJECTED NUMBER OF i

CYCLE TUBE REPAIRS

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l EOC 14 34 EOC 15 E

TOTAL 292 l

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CIRCUMFERENTIAL CRACK EXTENTS MILISTONE 2 STEAM GENERATOR TUBES FREQUENCY 30 1

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COMPARISON OF FEBRUARY 1989.AND OCTOBER 1989 NACK DETECTION CRITERIA l

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HINIMUM RPC SIGRAL LOWER THRESHOLD DUE TO AMPL CONFIRMED CRACK ANALYST CONSERVATISH BY FEB. UT EXAM OCTOBER CRITERIA:

RESULTS IN HORE FALSE CRACK CALLS THAN FEBRUARY o

CRITERIA 29 0F 104 RPC CRACKS CALLED NONCRACKS BY UT

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19/H2SG 02/22/90

9 HISTORY 0F CIRCUMFERENTIAL CkACKS AT MILLSTONE 2 INSPECTION

1. CRACKS

1. NEW CRACKS DATE IDENTIFIED DURING CYCLE E0C 7 1*

23 (NOV '86)

E00 8 26 227 (JAN '88)

EOC 9 309 99 (FEB '89)

IN-CYCLE 10 104 35

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TOTAL 440 384**

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1 N

t IMPROVENENTS IN CRACK DETECTION CAPABILITIES DCT0BER 1989 INSPECTION i

l o

EQUIPMENT:

4 LARGER RPC HOTOR/ CLEARER SIGNAL i

UT PERFORMED ON ALL "POSSIBLE" CRACKS BY t

RPC l

t o

ANALYSIS METHODS:

i TAPE REVIEW BY W O INDEPENDENT ANALYSTS i

1 ANALYST TRAINING / AWARENESS UPGRADE 1

I e

l 22/M2SG 02/22/90 i

l I

l i

i i

EXISTING CRACKS (IN-CYCLE 10)

.BECOMING DETECTABLE E0C 10 i

\\

o 25 EXPECTED BASED ON EXPECTED IN-CYCLE 10 DETECTION EFFICIENCY i

o NORMAL ECT REPEATABILITY VARIATIONS (IMPROVED i

i S/N) i l

l I

o DEPTH INCREASE TO DETECTABLE THRESHOLD i

l o

NOT STRUCTURALLY SIGNIFICANT IN-CYCLE 10 r

I s

)

23/M2SG 02/22/90

l StHRRY

}

i o

BOBBIN COIL, RPC AND UT WERE USED TO ASSESS THE CONDITION OF THE MP2 SG TUBES o

CRACK REGION B0UNDED BY OCTOBER RPC EXAH i

l o

THE CRACK DETECTION CRITERIA IMPLEMENTED IN i

OCTOBER IDENTIFIED SIGNIFICANT CRACKS i

i o

UT IDENTIFIED LIGAMENTS OF " GOOD" HETAL WITNIN THE MACR 0 CRACKS i

o AVERAGE PITTING GROWTN CONTINUED TO REMAIN AT VERY LOW LEVELS l

o NO LARGE VOLUME, LARGE DEPTN PITS IDENTIFIED i

l o

FUTURE REPAIRS DUE TO PITTING EXPECTED TO l

STEADILY DECREASE FROM 70 (E0C 10) TO 27 i

(EOC 15)

I 1

24/M2SG 02/22/90

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TUBE REMOVAL PROGRAM

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25/M2SG 02/22/90 I

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l BACKGROUND o

THREE TUBES WERE REMOVED FOR EXAMINATION DURING I

THE OCTOBER 1989 SHUTDOWN i

l I

o OBJECTIVES WERE TO DETERMINE CRACK HORPHOLOGY, EFFECTIVENESS OF CORRECTIVE ACTIONS, CAUSE OF l

CRACKING, AND BURST STRENGTH OF WORST CASE TUBE l

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l l

l L

1 26/H2SG 02/22/90

. - l 9

1 l

HELD EXAMINATIDMS o

BOBBIN C0IL o

ROTATING PANCAKE COIL o

ULTRASONIC l

l 4

1 o

EXPERIMENTAL PROBES (AW1, CECC0) l i

I i

[

e I

I 27/H2SG 02/22/90

4

+

4 k

LABORATORY EXAMINATIONS o

BURST TESTS o

SCANNING ELECTRON HICROSCOPY (SEM) o ENERGY DISPERSIVE SPECTROSCOPY (EDS) o VISUAL o

RADIOGRAPHY o

OPTICAL HETALLOGRAPHY '

o AUGER ELECTRON SPECTROSCOPY (AES) o X-RAY PHOT 0 ELECTRON SPECTROSCOPY (XPS) o BULK CHEMICAL ARALYSIS o

SLUDGE ANALYSIS o

TENSILE 1ESTS o

H0DIFIED HUEY TESTS 28/M2SG 02/22/90

~

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j

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BURST TEST RESULTS j

l i

o TUBE 2C L118/R14:

CRACKING 3600 l

BURST AXIALLY AT 11,200 psr l

i i

l o

TUBE 1C L52/R22:

i l

CRACKING 3050 l

LEAKED AT 8,500 Pst, DID NOT BURST.

o REGULATORY GUIDE MARGINS TO BURST FULLY HET (3 TIMES NORMAL OPERATING PRESSURE DIFFERENTIAL, 4125 Pst) i i

29/M2SG 02/22/90 4

t

1.

ADDITIONAL SURST TE.STS l

l o

A TOTAL 0F 9 EDM NOTCH REPLICAS WERE PRODUCED AND BURST TESTED j

o 2C L118/R14 AND 1C L52/R22 WERE REPLICATED SIX SPECIMENS WERE PRODUCED, WITH AVERAGE 1,

CRACK DEPTHS RANGING FROM 47 PERCENT TO 56 i

PERCENT ALL SIX SPECIMENS FAILED AXIALLY AT I

i PRESSURES AB0VE 11,000 Psr I

i j

o OTHER REPLICAS WERE PRODUCED AND BURST TESTED:

l A UNIFORM, 3600 CRACK AVERAGING 75%

l THROUGH-WALL BURST AT 10,100 psr l

i i

A NONUNIFORM CRACK AVERAGING 50%

l i

THROUGH-WALL LEAKED AT 12,000 psr (900 x 71% THROUGH-WALL, l

1800 x 65% THROUGH-WALL) 1 A NONUNIFORM CRACK AVERAGING 43%

l THROUGH-WALL BURST AXIALLY AT 12,000 Psr (2300 x 67% THROUGH-WALL) l.

o TUBES WITH SUBSTANTIAL CIRCUMFERENTIAL CRACKING l

STILL PROVIDE VIRGIN STRENGTH.

ALL SPECIMENS EASILY MET REG. GUIDE MARGINS TO BURST.

i l

l 30/M2SG 02/22/90 i

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.s NONDESTRUCTIVE vensus DESTRUCTIVE EXAMINATIORS LABORATURY TUBE FIELD _NDE DESTRUCTIVE EXAMINATION CtpselTS SG 2 COLD CRACK 291'8

_RPC)

AVG. 49% TW o BWST AXIALLY 11,290 ps

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l L118/R14 CRACK 740 x 80T TW MAX.71%Tg I

(10/89 MAX. (UT)

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IN-CYCLE)

F4M x 281 RF0 SY RFC

>M TW x 360' 16 SEPARATE MICit0 CRACKS 8

CRACK 191 AVG. 47% TW e

LEAKE9 AT S 500 est CRACKTT659(RPC)

SG 1 COLD GTAL MAX. 91% TW DURINGBUR5i i

L52/RZZ I

(10/89 x 80% TW MAX. (UT)

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IN-CYCLE)

>5M TW x 195*

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>M TW x 305 15 SEPARATE MICit00 TACKS 4

SG 1 COLD CRACK 88* E AVG. 19% TW o ROT E W ST TESTB i

L145/RZ3 CRACKT I45 9 0TAL MAX. 64% TW 1

(10/89 x 4M TW MAX. (UT)

>50%_TW x_49?

o 125' CRACK PRE 5DIT 91/91 IN-CYCLE)

>40% TW x 65"'

RF0 SY RPC (BASEB W i

>0% TW x 236 10/89 REAMLYSIS W 8 SEPARATE MICR00 TACKS 91/89 ORTA TWES)

SG 1 HOT CRACK 254'_(RPC)

AVG 73% TW e PLOGEED PM 1 YEW PRM L25/R19 CR M T B 4' x 100% TW MAX. 100%

TO RUENAL M 01/W (01/88 RFO)

MAX (UT) 100% TW x 1

>5M TW x 2

>M TW x 322"

>20 SEPAltATE MIOt00 TACKS l

32/M2SG 02/22/90

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i LIGAMENT CHARACTERISTICS

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CORR 0DED/

DUCTILE POSSIBLY CORR 0DED

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I SG 2 COLD 11 5

L118/R14 SG 1 COLD 14 1

L52/R22 l

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L145/R23 l

l o

79 PERCENT OF THE LIGAMENTS WERE DUCTILE j

q o

EVEN IN THE OLDEST CRACK (L145/R23), 75 PERCENT l

OF LIGAMENTS WERE DUCTILE j

o MOST LIGAMENTS REMAIN INTACT IN A STRUCTURAL ROLE i

i i

}

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l HICR0 ANALYTICAL RESULTS l

i o

CNEHICAL COMPOSITION OF 0XIDE FILM 4

l o

Nr/Cn, NA/Sr, Ps, S, NA; NO CONCLUSIVE CAUSATIVE SPECIES IDENTIFIED l

j o

SIGNIFICANT B (UP T0 6.2 ATOM PERCENT);

SUCCESSFUL DIFFUSION OF BORIC ACID INTO CREVICES t

l 37/M2SG 02/22/90

j SumARY j

i o

THE FLAWS WERE CONFIRMED T0 BE 0D INITIATED j

INTERGRANULAR STRESS CORR 0SION CRACKS.

)

o MP2 CRACKS AND VARIOUS REPLICAS OF WORST-CASE CONDITIONS EASILY MET REGULATORY GUIDE MARGINS

)

TO BURST.

1 l

o TUBES WITH SUBSTANTIAL CIRCUMFERENTIAL CRACKING i

l ARE CAPABLE OF PROVIDING VIRGIN STRENGTH.

(

o LIGAMENT HORPHOLOGY HAS BEEN OBSERVED IN ALL L

CRACKED HP2 TUBES REMOVED.

TUBES WITH LIGAMENTS i

ARE STRONGER THAN TUBES WITH CONTINUOUS CRACKS.

j o

MICR0 ANALYTICAL RESULTS WERE AMBIGUOUS.

I POSITIVE IDENTIFICATION OF CAUSATIVE SPECIES WAS NOT POSSIBLE.

1 o

BORIC ACID ADDITION SUCCESSFULLY ELEVATED CREVICE BORON.

o NDE CRACK PARAMETER ESTIMATES COMPARE REASONABLY WITH DESTRUCTIVE RESULTS.

l l

l l

38/H2SG 02/22/90

I i

i l

I

.i I

i l

I i

CORROSION HECHANISMS 1

AND THEIR IMPLICATIONS i

i t

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i f

i i

l l-r i

P i

i 5

i 39/M2SG 02/22/90

DETERMINATION OF CORROSION MECHANISM

~

i l

o ANALYSIS OF PROMPT HIDE 0UT RETURN AND OTHER DATA INDICATED CHEMISTRY HAD SHIFTED FRON ACIDIC 70 l

BASIC DURING CYCLE 7 AND REMAINED BASIC THROUGH 1

CYCLE 8.

MODELING INDICATES THAT THE IMPURITIES, WHEN CONCENTRATED, WOULD HAVE PRODUCED A CAUSTIC ENVIRONMENT IN THE SLUDGE AT i

THE TOP 0F THE TUBESHEET.

i i

l o

ECT INSPECTIONS AND REANALYSIS OF PREVIOUS INSPECTION DATA ESTABLISHED CRACKING TRENDS.

1 BEST FIT OF DATA IS TO A H0 DEL OF AN ACTIVE l

CAUSTIC CORROSION FOLLOWED BY AN EFFECTIVE B0RIC l

l ACID TREATNENT AND IMPROVEMENTS IN CHEMISTRY.

1 o

REMOVED TUBE EXAMINATION ESTABLISHED CORROSION MORPHOLOGY OF MICR0 CRACKS AND LIGAMENTS--

CONSISTENT WITH CAUSTIC CORROSION.

0XIDE FILM l

EXAMINATION RESULTS, IN CONJUNCTION WITH A REVIEW 0F POURBAIX DIAGRAMS, SUPPORT THE POSTULATED CORROSION HECHANISH.

i o

THE MAJORITY OF THE EVIDENCE INDICATES THAT CAUSTIC IS THE CAUSE OF THE CORROSION.

OTHER i

I ELEMENTS, SUCH AS LEAD AND SULFUR, MAY BE i

INVOLVED IN THE CORROSION PROCESS.

BORIC ACID COUPLED WITH IMPROVEMENTS IN CHEMISTRY APPEARS r

TO HAVE BEEN EFFECTIVE IN STOPPING THE CORROSION j

PROCESS.

1 1

l j

40/H2SG 02/22/90 i

MILLSTONE 2 STEAM GENERATORS l

HIDEOUT RETURN RATIOS l

AND TUBE REPAIRS nano

= nenues j

4 j

3M

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3--

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41/M2SG 02/22/90

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HIDEOUT RETURN RATIOS AND TUBE REPAIRS naso Twee nesswas

• 9 4289 (49 mHeep

- - p.opeggge eqNges

-3000 x

3--

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ACCELERATED LABORATORY TESTING i

f EFFECT OF RORIC ACID l

n (ll 3

INHIBITION OF CAUSTIC STRESS CORROSION CRACKING pf g [ g g / M M g f'; ien We 5CC Soric Acid Inhi'citjen M # ' ' M /[ d M

No8CC Tests hW///[l)Nh[b?))$ 91 NoSCC 17 Throughwall Cretking c

g e

30 40 60 80 too 130 440- 960 too too t

Days j

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PROPAGATION OF PRE-INITIATED i

CAUSTIC STRESS CORROSION CRACKING p

Initia P ro p g eflo n ~

I 39 Reforence See/AVT enty g

neforence see Test I

I I

I I

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o to ao -

so do so so to 80 Days to Produce Throughwall Crack 43/M2SG 02/22/90 4

L e-w

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L DIFFERENCES BETWEEN STEAM GENERATORS

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STRESS CORROSION HAS NOT OCCURRED UNIFORMLY IN THE MP2 SGs 87 PERCENT 0F THE CRACKING HAS OCCURRED IN F

SG 1 13 PERCENT OF THE CRACKING HAS OCCURRED IN SG 2

)

o MATERIAL HEATS FROM TWO VENDORS WERE USED IN THE CONSTRUCTION OF THE MP2 SG TUBES l

HUNTINGTON u

B&W HEATS ALLOY HEATS SG 1 98.8%

1.2%

t SG 2 5.0%

95.0%

o 0F THE AVAILABLE TUBES FROM EACH VENDOR, CRACKING HAS OCCURRED PREFERENTIALLY IN TUBES MADE FROM B&W HEATS.

PERCENT OF i

VENDOR AVAILABLE TUBES CRACKED B&W 4.45%

HUNTINGTON ALLOYS 0.57%

TUBES MADE FROM B&W HEATS APPEAR TO BE A FACTOR OF APPROXIMATELY 8 MORE SUSCEPTIBLE TO STRESS CORROSION THAN TUBES MADE FROM HUNTINGTON ALLOYS i

HEATS.

l o

TUBES MADE FROM B&W HEATS HAD HIGHER MATERIAL PROPERTIES ON AVERAGE THAN TUBE MADE FROM HUNTINGTON ALLOYS HEATS.

THIS INDICATES THAT THERE ARE INHERENT DIFFERENCES BETWEEN THE MATERIAL FROM THE TWO VENDORS WHICH SUPPORT THE OBSERVED DIFFERENCES IN CORROSION SUSCEPTIBILITY.

44/M2SG 02/22/90

MILLSTENE 2 STEAM GENERATOR C1

-4 vues Pia w sinass a

tutBSER OF TWSB8 8800 M MUN11Nef0N NEATS s000 E MWha' ate N

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Of S. StV. e bM1 pel 3500

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+

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i 86h00 87h00 99600 7d00 78500 76600 77000 79000 FLOW STRESS (PSI)

N MILLSTONE 2 STEAM GENERATOR #2 e

L Tust Flow stREsa Nuwstm er tutte 3000 m s&W NEAtt l

W3 HUNTINGTON HEATS y

870. DEV.

• Sate PSI 1600

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h 1000 s = m e B' B % @

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82 E3 BM E M E E

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66600 87600 49000 7dOO 73600 76b00 77d00 79600 FLOW STRESS (PSI) 45/M2SG 02/22/90

L-j 3

L i

t i

EXPECTED E0C 10 INSPECTION RESULTS i

o SOME NEW CRACKS WILL BE IDENTIFIED AT E0C 10.

INCIPIENT CRACKS WHICH FORMED DURING ACTIVE CAUSTIC CONDITIONS, PRIOR TO CYCLE 9, AND-PROPAGATE DURING CYCLE 10.

CRACKS CURRENTLY EXISTING BELOW NDE DETECTABILITY LEVELS WHICH BECOME l

DETECTABLE.

l i

o BEST ESTIMATE OF THE NUMBER OF CRACKS WHICH WILL BE IDENTIFIED AT THE EOC 10 REFUELING OUTAGE IS i

45.

l l

o IF ACTIVE CAUSTIC CORROSION WERE POSTULATED TO EXIST, OVER 1000 CRACKS WOULD HAVE BEEN EXPECTED BY THE IN-CYCLE 10 INSPECTION.

46/M2SG 02/22/90

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CAUSTIC CORROSION l

L i

l o

RATE OF THROUGH-WALL PENETRATION 0F INDIVIDUAL MICR0 CRACKS CAN BE RAPID COMPARED TO THE LENGTH j

OF A CYCLE.

J l

l o

THE CIRCUMFERENTIAL EXTENT AND DEPTH OF A MACROCRACK IS. CONTROLLED BY THE DISTRIBUTION 0F STRESSES, PRIMARILY RESIDUAL STRESSES, IN THE TUBE AT THE TOP 0F THE TUBESHEET.

l j

. o A DISTRIBUTION OF CIRCUMFERENTIAL EXTENTS, AS l

INDICATED BY.RPC, HAS BEEN OBSERVED.

THE L

DISTRIBUTION HAS REMAINED'THE SAME FOR EACH INSPECTION, REGARDLESS OF THE OPERATING TIME

^

BETWEEN THE INSPECTIONS.

THIS INDICATES THAT ONCE A MACROCRACK HAS FORMED, IT DOES NOT GROW i

SIGNIFICANTLY IN CIRCUMFERENTIAL EXTENT.

l 48/M2SG 02/22/90 t'

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CIRCUMFERENTIAL CRACK-EXTENTS..

MILLSTONE 2 STEAM GENERATOR TUBES numeen or cancxs -

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MACROCRACK CIRCUMFERENTIAL EXTENT j

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i 49M12SG 02/22/90

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CIRCUMFERENTIAL EXTENT OF CRACKS o

DISTRIBUTION 0F CIRCUMFERENTIAL CRACK EXTENTS CAN BE'MODELED BY A GA>NA DISTRIBUTION WITH A 0

MEDIAN OF 90, A MEAN OF 1020 AND A STANDARD DEVIATION 0F 679 l

o USING THIS MODEL, THE PROBABILITY 0F A CRACK OR i

CRACKS EXCEEDING A GIVEN CIRCUMFERENTIAL EXTENT l'

CAN BE DETERMINED.

THIS PROBABILITY VARIES WITH THE TOTAL NUMBER OF CRACKS ASSUMED TO BE PRESENT BY.THE END OF THE CYCLE.

l L

50/M2SG 02/22/90 L

L

- _ ~

s

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CIRCUMFERENTIAL CRACK EXTENTS.

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MILLSTONE 2 STEAM GENERATOR TUBES womeen or cancns 1.

m.=ve ne.

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MACROCRACK CIRCUMFERENTIAL EXTENT l

L 51/M2SG 02/22/90 p

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PROBABILITY.OF A SPECIFIC # OF CRACKS enosecibow h Nnacus soc so PROSABILITV EXPECTEDORMISER 100%

7 10 90% -

l 80%-

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8 70%-

l 60%-

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50%-

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PECTEFT ER t$rd 0%

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18 0 210 240 270 300 l

CIRCUMFERENTIAL EXTENT (DEGREES) 52/M2SG 02/22/90

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PROJECTED CIRCUMFERENTIAL CRACK EXTENTS ~

~

MILLSTONE 2 STEAM GENERATOR TUBES FOR A POPULMf0M OF 46 CRACK 8 EOC10 NtM08ER OF CRACKS 10 9N

+ e6% CONFIDENCE I

ses courmancE EXPECTED NUMBER

't 7

6 5

l 4

3 2

A 1 -

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I O

i 180 210 240 270-300 CIRCUMFERENTIAL EXTENT (DEGREES) e a

53/M2SG 02/22/90

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DEPTH 0F CRACKS o

PROFILES OF THE DEPTHS OF HACR0 CRACKS WERE DETERMINED BASED ON EXAMINATIONS OF REMOVED TUBES AND UT DATA.

o IN ORDER TO COMPARE CRACKS OF UNEQUAL CIRCUMFERENTIAL EXTENT, THE OBSERVED CORRODED AREA WAS AVERAGED OVER THE CIRCUHFERENCE OF THE TUBE TO OBTAIN AN EQUIVALENT DEPTH.

o THE EQUIVALENT DEPTH OF CIRCUMFERENTIAL CRACKS CAN BE USED TO PROVIDE A REASONABLE APPROXIMATION OF THE BURST STRENGTH OF THE TUBE.

CONSERVATIVE CALCULATIONS INDICATE THAT REGULATORY GUIDE 1.121 MARGINS ARE SATISFIED BY 1

A UNIFORM 77% THROUGH-WALL CIRCUMFERENTIAL CRACK.

o SIMILAR TO THE DISTRIBUTION OF CIRCUMFERENTIAL EXTENTS, THE DISTRIBUTION OF EQUIVALENT DEPTHS CAN BE MODELED BY A GA!44A DISTRIBUTION AND STATISTICAL INFERENCES HADE WITH REGARD TO THE DEPTHS OF CRACKS EXPECTED IN THE FUTURE.

54/M2SG 02/22/90 L

CIRCUMFERENTIAL CRACK DEPTHS.

MILLSTONE 2 STEAM GENERATOR TUBES UT EXAM MUMBER OF CRACKS 20 i

GAMMA DISTRWUTION N L25/R19 G.EAK) 15 W-ocTwmsPECTION MEAN = 22.3%

10 smwonne.evo ~,.. w.n 5

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5 10 ~ 15' 20 25 30 35 40 45 50 55 80 85 70 75 80 85 90 95100 i

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AVERAGE CRACK DEPTH (% THROUGHVWu.L) 55At2SG 02/22/90

w

• s-PROBABILITY OF A SPECIFIC # OF CRACKS.

EEEEgpECTI R

SE TO PnosaavuTv expectro aveseen l

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i 90%

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-TK 80%

4 l.

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80%

Exp Nous 1

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2 l

30%

20%

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0 45 50 55 60 65 70 77 AVERAGE DEPTH (% THROUGHVELtJ 56/N2SG 02/22/90

d d

,e PROJECTED CIRCUMFERENTIAL CRACK DEPTHS MILLSTONE 2 STEAM GENERATOR TUBES FOR A POPULArlON OF 46 CRACKS EOCM i

nousEn Or cRacus 8

73

+ 96% CONFIDENCE I

90% CONFIDENCE l

6-

+ EXPECTED nut!9EN 5

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46 50 55 60 65 70 77 I

MERAGE DEPTH (% THROUGH1Wu.L)

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i SOME OBSERVATIONS OF THE SIGNIFICANCE OF LARGE CIRCUMFERENTIAL CRACKS 5

o CIRCUMFERENTIAL CRACKS ARE LESS CHALLENGING THAN EQUIVALENT LENGTH AXIAL CRACKS.

PRESSURE FORCES PRODUCE HOOP STRESSES TWICE THE AXIAL STRESSES.

a o

TUBESHEET PROVIDES RESTRAINT TO BULGING 0F THE.

TUBE.IN THE REGION OF THE CRACK.

THE STIFFNESS i

0F THE TUBE, THE SURROUNDING TUBE BUNDLE, AND THE TUBE SUPPORTS RESTRAIN BENDING 0F ASYR4ETRIC CIRCUMFERENTIAL CRACKS.

q o

THE PRESENCE OF LIGAMENTS AND MICR0 CRACKS AT

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DIFFERENT ELEVATIONS SIGNIFICANTLY CONTRIBUTE TO THE STRENGTH OF THE CRACKED TUBE.

o THE TUBE WILL FAIL AXIALLY IN A BURST TEST WITH CIRCUHFERENTIAL CRACKS UP TO AN EQUIVALENT UNIFORM DEPTH OF APPROXIMATELY 58 PERCENT THROUGH-WALL.

L l

58/M2SG 02/22/90 l

SIGNIFICANCE OF MILLSTONE 2 CIRCUMFERENTIAL CRACKS

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o LARGEST CIRCUMFERENTIAL CRACKS IDENTIFIED IN NP2 1

TUBES BASED.ON OCTOBER 1989 UT AND RPC i

INSPECTIONS AND REMOVED TUBE EXAMINATIONS:

l CIRC.

i EQUIVALENT EXTENT HBE DEPTH (RPC)

L25/R19 (LEAKING TUBE) 73%

2540 L45/R13 70%

1390 l

L28/R36 60%

2570 L118/R14 (FAILED AXIALLY IN 49%

2910 l

BURST TEST AT 11,200 PSD l.

L52/R22 (LEAKED IN BURST TEST 47%

1910 L

AT 8,500 PSD L36/R32 38%

2960 ALL OTHERS 555%

52500 L

l o

IN ALL CASES BUT ONE (STILL UNDER EVALUATION),

REGULATORY GUIDE 1.121 MARGINS TO BURST WERE L

SATISFIED AND IN ALL BUT THREE CASES THE TUBE WOULD FAIL AXIALLY IN A BURST TEST WITH NO LOSS OF MARGIN o

WITH 95 PERCENT CONFIDENCE, NOT MORE THAN ONE OF THE 45 CRACKS PREDICTED TO BE IDENTIFIED AT THE E0C 10 REFUELING OUTAGE WILL HAVE AN EQUIVALENT DEPTH >77 PERCENT AND NOT MORE THAN TWO CRACKS WILL HAVE CIRCUMFERENTIAL EXTENTS >3000 59/M2SG 02/22/90

p g-SlHRRY o

THE STRESS CORROSION CRACKING WHICH HAS OCCURRED IN THE MP2 SG TUBES IS WELL UNDERSTOOD AND PREDICTABLE.

t o

CAUSTIC CONTINUES TO BE THE BEST ESTIMATE OF THE 4

CAUSE OF THE CORROSION.

OTHER ELEMENTS, SUCH AS

^

LEAD AND SULFUR, MAY BE INVOLVED IN THE CORROSION PROCESS.

?

o BORIC ACID TREA1NENT COUPLED WITH CHEMISTRY IMPROVEMENTS APPEARS TO HAVE BEEN EFFECTIVE IN CONTROLLING THE CORROSION.

j o

BEST ESTIMATE IS THAT 45 CRACKS WILL BE IDENTIFIED AT EOC 10, INCLUDING A FEW CRACKS i

WITH LARGE CIRCUMFERENTIAL EXTENTS AND DEPTHS.

NOT MORE THAN ONE CRACK IS EXPECTED TO EXCEED 77 PERCENT IN AVERAGE DEPTH AT THE 95 PERCENT CONFIDENCE LEVEL.

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J 60/M2SG 02/22/90 1'

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STRUCTURAL CONSIDERATIONS

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l MILLSTONE 2 TUBE INTEGRITY ANALYSIS l

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A STRUCTURAL INTEGRITY ANALYSIS WAS PERFORMED ON o

THE 86 CRACKED TUBES FOR WHICH UT DATA WAS AVAILABLE l

o TUBES WERE EVALUATED IN THREE CATEGORIES-TUBES WITH UNIFORM PART THROUGH-WALL CRACKS OVER 3600 TUBES WITH COMPLEX CRACKING THAT CAN CONSERVATIVELY BE COMPARED TO LIMIT LOAD CRITERIA l

l TUBES WHICH REQUIRED A MORE DETAILED l

EVALUATION l

o CATEGORY 1 TUBES WERE EVALUATED VERSUS AN ALLOWABLE FLAW DEPTH OF 77%

26 TUBES WERE ACCEPTABLE 0 TUBES WERE UNACCEPTABLE o

CATEGORY 2 TUBES WERE ASSUMED TO BE 100%

THROUGH-WALL OVER THE ENTIRE LENGTH OF THE DEEPEST FLAW AND UNIFORM CRACKING AROUND THE REMAINDER OF THE TUBE 38 TUBES WERE ACCEPTABLE 1 TUBE REQUIRED FURTHER EVALUATION 62/M2SG 02/22/90

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MILLSTONE 2 TUBE INTEGRITY ANALYSIS c

o CATEGORY 3 FLAWS WERE MODELED "AS-CALLED" FROM l

n UT DATA.

TUBE STRESSES WERE COMPARED TO FLOW i

STRESS FOR MP2 MATERIAL l

o CATEGORY 3 FLAWS WERE EVALUATED VERSUS THE MINIMUM MP2 FLOW STRESS, 65,000 xsr 15 TUBES WERE ACCEPTABLE l

t 7 TUBES HAVE LESS THAN THE REQUIRED FACTOR I

0F SAFETY, INCLUDING THE ONE TUBE FROM CATEGORY 2 l

l L

o BURST TESTS WERE PERFORMED AND THE RESULTS MODELED CONSISTENTLY WITH THE OTHER TUBES o

THE MINIMUM CORRECTION FACTOR TO ACHIEVE AGREEMENT BETWEEN THE MODEL AND TESTS WAS 1.68; MOST WERE >2.0 SINCE AXIAL FAILURE PRECLUDED CIRCUMFERENTIAL FAILURE o

EVALUATION OF CORRECTION FACTOR AND ANALYTICAL

+

RESULTS YIELD 6 TUBES WERE ACCEPTABLE; 1 TUBE (L45/R13) FALLS BELOW FAULTED PRESSURE OF 3150 PSI o

PRIMARY MEMBRANE STRESSES ARE ACCEPTABLE; MARGIN OF 1.37

.o 3D ANALYSIS TO EVALUATE EFFECT OF AXIAL SEPARATION IS BEING EVALUATED 63/M2SG 02/22/90

MP-2 S/G TUBE INTEGRITY LIMITS

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LIMIT LOAD ANALYSIS THRU-WALL CRACK LENGTH (DEGREES) 200 150 100 t

50 0

O O2 0.4 0.6 0.8 1

THRU-WALL DEPTH / TUBE WALL THICKNESS LIMIT LOAD CURVE i

REVISED 2/18/90 64/M2SG 02/22/90

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OPERATIONAL HONITORING e

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70/M2SG 02/22/90

OPERATIONAL MDNITORING o

,HILLSTONE UNIT 2 !$ SENSITIVE T0 STEAM GENERATOR LEAKAGE AND THE METHODS 0F DETECTION o

LEAK DETERMINATION BY:

STEAM JET AIR EJECTOR (SJAE) RADIATION HONITOR 2

I STEAM GENERATOR BLOWDOWN RADIATION N0NITOR 1

i MAIN STEAM LINE RADIATION HONITOR N16 STEAM LINE MONITORS

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ROUTINE GRAB SAMPLES (DAILY) l REACTOR COOLANT SYSTEM CALCULATED LEAK RATE PRIMARY-TO-SECONDARY TRITIUM BALANCE i

(DAILY) o VALUES FOR ALL 0F THE ABOVE, EXCEPT HAIN STEAM i

LINE RADIATION HONITORING AND TRITIUM BALANCE, ARE REVIEWED BY PLANT MANAGEMENT DAILY AS PART i

L OF THE PUBLISHED HORNING REPORT i

L I

i o

PROCEDURES AND ANALYZING TECHNIQUES UTILIZING THE SJAE, BLOWDOWN, AND GRAB SAMPLES WERE AVAILABLE AND PROVED EFFECTIVE IN IDENTIFYING LEAKS WHICH CAUSED FORCED SHUTDOWNS IN 1983 (APPROXIMATELY 0,35 opM) AND 1987 (APPROXIMATELY 0,15 opM) l 71/M2SG 02/22/90 l

OPERATIONAL MDNITORING o

N16 RADIATION MONITORS ARE INSTALLED ON BOTH MAIN STEAM LINES.

THEY HAVE BEEN CONTINU0USLY l

IN SERVICE THIS CYCLE AND HAVE PRODUCED LEAK RATERESULTSCONSISTENTWITHTHOSECALCglATEDBY THENgDGRABSAMPLES(0.0706.0x10-SJAE GPN).

RESULTS ARE RECORDED ON A "PER $NIFT" BASIS AND DISPLAYED ON INSTRUMENTATION LOCATED DIRECTLY OUTSIDE THE CONTROL ROOM, CONVENIENT TO OPERATIONS PERSONNEL, WHENEVER SJAE RAD!

HONITORALARMSARERECEIVED,ADDg!0N l

READINGS ARE RECORDED.

FUTURE N SYSTEM l

ENNANCEMENTS ARE ANTICIPATED TO INCLUDE CONTROL l

R00H ALARMS 1

o SJAE AND BLOWDOWN RADIATION MONITOR ACTIVITY IS CONTINU0USLY HONITORED.

SET P0INTS ARE i

ESTABLISHED AND REQUIRE OPERATOR ACTION AND SUBSEQUENT GRAB SAMPLE CONFIRMATION 1

o MILLSTONE UNIT 2 NAS AN INCREASED AWARENESS AND SENSITIVITY TO LEAK DETECTION METHODS AND THEIR l

IMPLICATION WITN RESPECT TO TUBE CRACKING l

72/H2SG 02/22/90

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l CONCLUSIONS

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73/M2SG 02/22/90 i

[

o

• a CONCLtJSIONS o

ALL DEFECTS IDENTIFIED DURING OCTOBER 1989 OUTAGE CORRECTED 1

o PITTING AND CRACKING 0F TUBES EXHIBIT ACCEPTABLE i

LEAK BEFORE BREAK BEHAVIOR j

l o

STRUCTURAL INTEGRITY OF THE TUBE PRIMARY l

PRESSURE BOUNDARY IS MAINTAINED PROVIDED THE l

0,1 sPM LEAKAGE LIMIT IS NOT EXCEEDED l

o LEAKAGE IN EXCESS OF THE TECHNICAL SPECIFICATION l

LIMITS REQUIRES SHUTDOWN OF THE UNIT l

l

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I o

ALL APPLICABLE REGULATORY GUIDELINES ARE MET i

WITH THE EXCEPTION OF 1 CRACK AS PREVIOUSLY DISCUSSED o

CONTINUED OPERATION FOR REMAINDER OF CYCLE 10 IS i

APPROPRIATE l

I 74/M2SG 02/22/90 f