Text

Summary of 890316 Meeting W/Util in Rockville,Md Re Steam Generator Tube Insp at Plant.List of Attendees Encl
	ML20245C138
Person / Time
Site:	Millstone
Issue date:	04/10/1989
From:	Vissing G; Office of Nuclear Reactor Regulation
To:	; Office of Nuclear Reactor Regulation
References
	NUDOCS 8904270022
	Download: ML20245C138 (76)
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s L PCfog p Q([ gg o UNITED STATES NUCLEAR REGULATORY COMMISS!ON 2 i,n;p ' d l WASHINGTON, D. C. 20555

TW/ ..... April 10, 1989 '

Docket No. 50-336 I LICENSEE: Northeast Utilities -

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FACILITY: Millstone, Unit No. 2

SUBJECT:

SUMMARY

OF MEETING WITH REPRESENTATIVES OF NORTHEAST UTILITIES CONCERNING THE STEAM GENERATOR TUBE INSPECTION AT MILLSTONE 2, MARCH 16, 1989 INTRODUCTION l

On March 16, 1989 representatives of the NRC and Northeast Utilities met in I the NRC office in Rockville, Maryland to review and discuss the ongoing steam i generator tube inspection activities at Millstone, Unit No. 2. The attendance list is provided in Enclosure 1. A copy of the slide presentation is provided in Enclosure 2.

DISCUSSION The agenda and presentation was as indicated in Enclosure 2. The licensee has performed a 100% eddy current inspection to the first support of the tubes ends (24,593) of both steam generators. This was done with a bobbin type coil. In addition they have full length inspected 4,237 tubes. They also inspected every tube with the rotating pancake coil in the sludge area of the tube bundle where most of the cracks are located. They identified 309 tubes with circumferential cracks ranaing from 14 degrees to 329 degrees and 125 tubes with pits greater than 40% through wall. Most of the cracks and pits were in the sludge area of the hot leg. The licensee believes that of the 309 cracks identified at the end of cycle 9, 2/3 were present at the end of cycle

8. They believed that improved inspection techniques for this outage identified these cracks. The cracks were not continuous but made up up of clusters of micro cracks. For this reason they believe a tube would leak before it would break.

Within two months of cycle 9 operation the licensee operated with boron in the secondary side to reduce the caustic nature of the secondary side. They believe that this arrested the growth rate of cracks. They believe that the cracks were the result of caustic stress corrosion during operating cycles prior to cycle 9.

The technical specification limit for leakage is 0.1 gpm. Considering the leak before break theory, the low TS limit for leakage and that very few of the cracks identified would have been developed during cycle 9, the licensee concludes that steam generator tube integrity is assured through cycle 10.

CONCLUSION The staff is concerned about the number of circumferential cracks, the uncertainty regarding existing corrosion rates, that cycle 10 will be 80 days longer than cycle 9 and the reliance on the leak before break theory. The staff is also concerned if the addition of boron has indeeo arrested the corrosion process and that circumferentiai cracks give concern for a potential

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8904270022 090410 1 PDR ADOCK 05000336 /t O PNU

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tube rupture in the_ crack region which could propagate into multiple tube

failures. The licensee does not intend to plan for a mid-cycle inspection or reduction of the-limit of the leak rate which was recommended by the staff.

The meeting ended with the indication from the staff that we would respond after meeting with our management. The licensee requested this be in writing.

/s/

Guy S. Vissing, Project Manager Project Directorate I-4 Division of Reactor Projects I/II

Enclosures:

As stated cc w/ enclosures See next page DISTRIBUTION "Doctet211es..,

.c NRC~& Local ^PDRs J. Sniezek Plant File J. Stolz G. Vissing 0GC .

E. Jordan B. Grimes NRC Participants ACRS (10)

H. B.'Clayton (Region I)

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tube rupture in the crack region which could propagate into multiple tube failures. The licensee does not intend to plan for a mid-cycle inspection or reduction of the limit of the leak rate which was recommended by-the staff.

The meeting ended with the indication from the staff that we would. respond after meeting with our management. . The licensee requested this be in writing.

Guy S. Vissing, P ject Manager Project Directorate I-4 Division of Reactor Projects I/II

Enclosures:

As stated cc w/ enclosures See next page I

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Mr. Edward J. Mroczka Millstone Nuclear Power Station Northeast Nuclear Energy Company Unit No. 2 cc:

Gerald Garfielc', Esquire R. M. Kacich, Manager Day, Berry and Howrid Generation Facilities Lic~ensing Counselors at Law Northeast Utilities Service Company City Place Post Office Box 270 Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. O. Nordquist Nuclear Operations Manager of OnI!ty Assurance Northeast Utilities Service Company Northeast Nuclear Energy Company Post Office Box 270 Post Office Box '70 HartfoYd, Connecticut 06141-0270 Hartford, Conner + . cut 061al-0270 Kevin McCarthy, Director Regional Administrator.

Radiation Control Unit Region I Department of Environmental Protection U. S. Nuclear Regulatory Commission 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 80 Washington Street 200 Boston Post Road Hartford, Connecticut 06106 Waterford, Connecticut 06385

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S. E. Scace, Station Superintendent W. J. Raymond,-Residerl Inspector Millstone Nuclear Power Station Hillstone Nuclear Power Station Northeast Nuclear Energy Company c/o U. S. K:. clear Regulatory Commission Post Office Box 128 Post Office Box 811 Waterford, Connecticut 06385 Niantic, Connecticut 06357

_ J. S. Keenan, Unit Superintendent Charles Brinkman, Manager Millstone Unit No. 2 Washington Nuclear Operations Northeast Nuclear Energy Company C-E Power Systems Post Office Box 128 Combustion Engineering. Inc.

Waterford. Connecticut 06385 '

12300 Twinbrook Pkwy Suite 330 Rockville, Maryland 20852 i

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ATTENDANCE LIST FOR MEETING WITH NORTHEAST UTILITIES CONCERNING STEAM GENERATOR TUBE INSPECTION FOR MILLSTONE UNIT NO. 2 MARCH 16, 1989 -

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NAME ORGANIZATION Guy S. Vissing NRR/NRR/PDI-4 Jack Strosnider NRC/ Region I C. Y. Cheng NRC/NRR/ DEST /EMTB Emmett Murphy NRC/NRR Jim Benson NUSCO

, Fred Ducino NNECO R. Thomas Blanchard Jr. NNECO J. M. Fackelmann Nuc. MTl/Ch (NUSCO)

Fred Anderson NUSCO Jay F. Eg .

NUSCO William E. Hutchins NUSCO Frank Witt NRC/ DEST /ECEB H. Conrad NRC/ DEST /EMTB

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l NORTHEAST NUCLEAR ENERGY COMPANY HILLSTONE UNIT NO. 2 DOCKET #50-336 MARCH 16, 1989 HEETING WITH NRC STAFF STEAM GENERATOR TUBE ECT RESULTS

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NRC MEETING AGENDA MILLSTONE 2 STEAM GENERATOR EXAMINATION 3 1989 REFUELING OUTAGE I INTRODUCTION GENERATION FACILITIES ~

LICENSING 4

WILLIAM E. HUTCHINS INSPECTION PROGRAM, NUCLEAR MATERIALS & CHEMISTRY RESULTS JIM BENSON CHEMISTRY NUCLEAR MATERIALS & CHEMISTRY CONSIDERATIONS J0E FACKELMAN i

CRACK MECHANISM NUCLEAR MATERIALS & CHEMISTRY FRED ANDERSON STRUCTURAL PIPING SYSTEMS ENGINEERING CONSIDERATION JAY ELY LEAK MONITORING ' PLANT R. THOMAS BLANCHARD l

OVERALL CRACK NUCLAR MATERIALS & CHEMISTRY ASSESSMENT J0E FACKLEMAN

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SU N RY GENERATION FACILITIES LICENSING !

WILLIAM E. HUTCHINS i

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PURPOSE OF MEETING .

0 TO REPORT THE RESULTS OF EDDY CURRENT TESTING CONDUCTED DURING THE 1989 REFUELING OUTAGE.

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TESTING TECHNIQUES /RESULTS LEAK RATE MONITORING PROGRAM PLUGGING & SLEEVING PROGRAMS l 0 TO DEMONSTRATE THE NNEC0 CONCLUSION THAT HILLSTONE UNIT NO. 2 SG TUBE INTEGRITY IS ASSURED FOR OPERA-TION THROUGH CYCLE.10.

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,4 STEAM GENERAT^". EXAMINATION SCOPE TEST DESCRIPTION # 0F TESTS % OF POPULATION ,

BOBBIN TO FIRST 24,593 TUBE ENDS 100%

SUPPORT BOBBIN FULL LENGTH 4,237 TUBES 29%

SEGMENTED BOBBIN APPR0X. 1,000 TUBES 20%

ROTATING PANCAKE 12,556 TUBE ENDS 100% WITHIN COIL CRACK BOUNDARY ULTRASONIC TEST 10 TUBE ENDS i

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SUW4ARY OF DATA ANALYSIS TECHNIQUES 0 ALL ANALYSTS WERE TRAINED AND QUALIFIED TO PLANT-SPECIFIC DATA ANALYSIS GUIDELINES PRIOR TO THE EXAMINA-TION

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PROVIDES THE QUALIFIED ANALYST WITH THE OPTIMUM METHODS OF RECOGNIZING AND REPORTING EDDY CURRENT DATA AT MP2 ENSURES THAT DATA IS ANALYZED AND REPORTED IN A CONSISTENT AND REPEATABLE MANNER 0 AN INDEPENDENT REVIEW OF ALL DATA WAS PERFORMED 0 COMPUTERIZED DATA ANALYSIS WAS IMPLEMENTED AS A SECOND- ,

ARY REVIEW OF THE B0BBIN COIL DATA i PROVIDES CONSISTENT, REPEATABLE RESULTS .

ELIMINATES ANALYST " FATIGUE FACTOR" l

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LOCATION 0F TUBE FLAWS AT HILLSTONE 2 i BEGIDE -

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A - CRACKING AT TTS l

B - SHALLOW BANDS OF PITS l C - SMALL VOLUME, ISOLATED PITS V FIRST EGGCRATE SUPPORT ANNN \\N\NNi {

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SHALLOW BANDS OF PITS 0% THROUGH WALL AVERAGE GROWTH DURING CYCLE 9 0 PREVIOUSLY EXISTING ABOVE TUBESHEET PITTING

(> 1" ATS)

SINGLE, IS01.ATED PITS SMALL VOLUME 2% THROUGH WALL AVERAGE GROWTH DURING CYCLE 9 0 NEWLY IDENTIFIED ABOVE TUBESHEET PITTING

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APPROXIMATELY 30 LARGER VOLUME, LARGER DEPTH DEFECTS INITIATED DURING CYCLE 9 LOCATED IN THE COLD LEG PLENUM OF EACH STEAM

! GENERATOR LOCATED FROM 1" TO 3" ABOVE TUBESHEET ASSOCIATED WITH OD COPPER DEPOSITS

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SUINARY OF STEAM GENERATOR TUBE CRACKING 0 309 TUBE ENDS CONTAINED CRACKS

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THE CRACKS WERE CIRCUHFERENTIALLY ORIENTED AND WERE LOCATED AT THE TOP 0F THE TUBESHEET 0 85% OF THE CRACKING OCCURRED IN STEAM GENERATOR 1 l l

0 EACH CRACK IS MADE UP 0F SEVERAL HICR0 CRACKS l WITH THE OVERALL CRACK EXTENT RANGING FROM yo 146 l 3290 BY MRPC 0 BASED ON A SAMPLE COMPARISON OF 1988 AND 1989 EDDY CURRENT DATA:

90%.0F THE HOT LEG CRACKS WERE PRESENT AT THE END OF CYCLE 8 33% OF THE COLD LEG CRACKS WERE PRESENT AT THE END OF CYCLE 8 i

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REASON FOR NOT IDENTIFYING CRACKING IN 1988 0 THE 26 WORST CASE CRACKS WERE IDENTIFIED AND

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REMOVED FROM SERVICE IN 1988 j 0 LABORATORY STUDIES ON CRACK SAMPLES AND PULLED TUBE NDE PROVIDED CRITERIA FOR CRACK DETERMINATION (1988 REFUELING OUTAGE) 0 IMPROVED TECHNOLOGY IN 1989 (I.E. SLOWER PROSE SPEED) ALLOWED FOR BETTER CRACK DETECTION l

0 IMPROVER KNOWLEDGE OF CRACK SIGNAL DETERMINATION {

BY MRPC LAS GAINED BASED ON A COMPARIS0N OF MRPC !

AND UT TEST RESULTS IN 1989 0 THE CRITERIA FOR CRACK DETERMINATION IN 1989 WAS L MUCH " TIGHTER" THAN THAT USED IN 1988 l 9

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SutNARY OF ULTRASONIC EXAMINATION RESULTS 0 10 TUBES WITH " CRACK LIKE" MRPC INDICATIONS IN SG L

1-CL WERE TESTED BY UT TO CONFIRM MRPC RESULTS O COTH AXIAL AND 00 SCANS WERE PERFORMED.

O CRACKS WERE IDENTIFIED IN ALL 10 TUBES 0 EACH " CRACK" CONSISTED OF SEVERAL' DISCONTINUOUS ,

AND CONNECTED MICR0 CRACKS 0 IN SOME CASES, THE MICR0 CRACKS WERE AT DIFFERNT AXIAL PLANES 0 ALTHOUGH BETTER THAN MRPC AT DEFINING LIGAMENTS BETWEEN CRACKS., THE UT MAY NOT RESOLVE ALL LIGA-HENTS 0 A RANDOM UT EXAMINATION OF 22 SG 1-HL TUBES IN 1988 DID NOT IDENTIFY ANY CRACKS 1

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4i COMPARISON OF UT AND MRPC EXAMINATION RESULTS

- CRACK LENGTH MEASUREMENTS *

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CRACK BOUNDARY DETERMINATION 0 100% OF THE HOT AND COLD LEG TUBE ENDS WERE. TESTED WITH B0BBIN PROBE (24,593) - .

q 0 ALL B0BBIN C0IL " DISTORTED ROLL INDICATIONS" (DRI)

WERE TESTED BY MRPC (323) 0 25% OF THE DRI TUBE END CONTAINED CRACKS 0 A CRACK REGION BOUNDARY (12,362 UNPLUGGED, UNSLEEVED TUBE ENDS) WAS DEFINED BASED ON LOCATION OF CRACKS IDENTIFIED BY THE DRI CRITERIA HIGH SLUDGE REGION IN CENTER OF STEAM GENER-ATOR -

J 0 100% OF ALL TUBES WITHIN BOUNDARY WERE TESTED BY MRPC 0

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l SUlelARY OF TUBE PLUGGING 1989 MILLSTONE 2 STEAM GENERATOR EXAMINATION 1
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REASON FOR STEAM GENERATOR PLENUM l
PLUGGING SG 1-HL SG 1-CL SG 2-HL SG 2-CL TOTAL
TTS CRACK 157 106 34 12 309 f/"
2 40% TW DEFECT 19 37 15 54 125 (NON-CRACK)
.540" PROBE 1 0 8 0 9 RESTRICTION (ENTRY SIDE)
NO ACCEPTABLE 2 0 5 0 7 M' MRPC EXAM WITHIN CRACK REGION EXCESSIVE TUBE O 0 0 3 3'#
NOISE ,
TOTAL TUBES 304 .129 433
SOME TUBES REQUIRE REPAIR FOR MORE THAN ONE REASON.
SUl4%RY/ CONCLUSIONS 0 A THOROUGH INSPECTION OF ALL REGIONS OF THE STEAM GENERATORS WAS PERFORMED, USING STATE-0F-THE-ART NDE !
TECHNIQUES I i
0 REINSPECTION ANALYST TRAINING AND INDEPENDENT DATA.
REVIEWS ASSURED THAT ACCURATE AND CONSISTENT TEST RESULTS WERE ACHIEVED.
0 ESSENTIALLY ALL TUBE FLAWS (PITS AND CRACKS) WERE i LOCATED ABOVE THE TUBESHEET WITHIN THE HIGHER SLUDGE REGION 0 HOT LEG PITTING IS NONACTIVE O COLD LEG PITTING IS NONACTIVE, EXCEPT: IN A DISCRETE REGION (1" TO 3" ATS); AND ONLY ON A SMALL NUMBER OF TUBES 0 MOST CRACK " GROWTH" OCCURRED:
PRIOR TO CYCLE 9 IN THE HOT LEG FLENUMS DURING CYCLE 9 IN THE COLD LEG PLENUMS 0 IMPROVED MRPC DATA ACQUISITION AND ANALYSIS TECHNIQUES RESULTED IN THE IDENTIFICATION OF CRACKS WHICH WOULD NOT HAVE BEEN IDENTIFIED DURING THE 1988 STEAM GENERATOR EXAMINATION 0 BASED ON UT, EACH " CRACK" CONSISTED OF SEVERAL MICR0 CRACKS, ALTHOUGH THE MRPC INSPECTION TECHNIQUE COULD NOT RESOLVE EACH INDIVIDUAL CRACK h THE " CRACK BOUNDARY" WAS SHOWN TO ENCOMPASS ALL TUBES CONTAINING CRACKS, BASED ON 100% BOBBIN AND 5% MRPC SAMPLES OUTSIDE THE BOUNDARY 0 A TOTAL OF 433 TUBES REQUIRED PLUGGING FOR VARIOUS REASONS l
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MILLSTONE 2 CHEMISTRY 0 HIDEOUT RETURN / NORMAL OPERATIONS:
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CAUSTIC IDENTIFIED DURING CYCLE 8 LIKELY PRESENT DURING CYCLE 7 1
SULFUR DECREASED BY AN ORDER OF MAGNITUDE 4 SINCE USE OF REVERSE OSMOSIS. !
l MINIMAL LEAD TRANSPORT AT MILLSTONE 2 (APPEARS NORMAL FOR PWR). j COPPER ALLOYS REPLACED.
O LEAD, SULFATE, COPPER HAVE ALWAYS BEEN PRESENT AS CONTAMINANTS. ONSET OF CAUSTIC HAS CREATED AN ENVIRONMENT WHICH PROMOTES SCC.
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MILLSTONE 2 STEAM GENERATOR CRACKING O TOTAL 0F 3361,UBES (INCLUDING LEAKING TUBE L25/R19) HAVE BEEN IDENTIFIED AS CONTAINING j CIRCUMFERENTIAL ORIENTED CRACKS q O THE CRACKS ARE LOCATED AT THE TOP 0F THE TUBESHEET IN.THE SLUDGE PILE REGION OF ALL STEAM GENERATOR PLENUMS 0 THE CRACKS ARE CAUSED BY 0.D. INITIATED STRESS CORROSION .
O LOCATION AND CLUSTERING 0F DEFECTIVE TUBES INDICATES A GLOBAL STRESS EFFECT 0 ANALYSIS OF ALL AVAILABLE DATA INDICATES CAUSTIC AS MOST LIKELY CORROSIVE SPECIES, POSSIBLY ACCELERATED BY COPPER r
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REVIEW 0F AVAILABLE DATA
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0 EXAMINATION OF LEAKING TUBE SG 1 L25/R19 REMOVED EOC 8 i
0 PLANT OPERATING EXPERIENCE l ECT INSPECTIONS LEAK MONITORING CHEMISTRY '
l 0 TUBE STRESS ANALYSIS FOR MP2 SG'S ,
1 0 FIBER OPTIC EXAMINATION E00 9 0 LABORATORY TEST DATA DEGRADED EGGCRATE PROGRAM BORIC ACID TREATHENT QUALIFICATION INCONEL 600 SCC DATA BASE l 0 OPERATING EXPERIENCE AT OTHER PLANTS REMOVED TUBE EXAMINATIONS BORIC ACID TREATNENT EXPERIENCE BURST TESTS OF REMOVED TUBES S
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. REVIEW 0F EXAMINATION OF TUBE SG 1 L25/R19 O TUBE HISTORY INSPECTED E0C 7--30% FLAW DETECTED--N0 CRACK DETECTED
" TUBE LEAKED AT 0.1 GPM (INITIAL RATE).APPROXI-MATELY 6 WEEKS AFTER START-UP _
ECT IDENTIFIED CIRCUMFERENTIALLY ORIENTED DEFECT (APPROXIMATELY 2500)
TUBE PLUGGED / SURROUNDING TUBES. STAKED TUBE REMOVED FOR EXAMINATION.E0C 8 0 EXAMINATION RESULTS THE LEAK WAS CAUSED BY A CIRCUNFERENTIALLY ORIENTED OD IH11IfTED INTERGRANULAR STRESS CORROSION CRACK-THE EXTENT OF THE CRACK WAS:
0 100% THROUGHWALL OVER 1900 0 > 50% THR00GHWALL-0VER 2600 0 1000 0F SEPARATE MICR0 CRACKS
< 50% THROUGHWALL 0 FIELD NDE ACCURATELY DESCRIBED THE CIRCUMFERENTIAL EXTENT > 50% THROUGHWALL, BUT DID NOT DETECT SHALLOW PORTIONS OF THE CRACKING i 0 CAUSTIC, LEAD, AND SULFUR WERE IDENTIFIED AS POSSIBLE CORROSIVE SPECIES (EXAMINATION'COMPLI-
, CATED BY THE TIME IN SERVICE WHILE PLUGGED)
CAUSTIC CONSIDERED THE MOST LIKELY CORROSIVE SPECIES 0 MULTIPLE CRACK INITIATION SITES WITH LIGAMENT MATERIAL BETWEEN CRACKS IDENTIFIED 0 DEVELOPMENT OF MODEL OF CRACK PROGRESSION j
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,. DESTRUCTIVE EXAMINATIONS -
L25/R19 -- -
O SCANNING ELECTRON HICROSCOPY 0 ENERGY DISPERSIVE SPECTROSCOPY (EDS) 0 OPTICAL METALL0 GRAPHY 0 AUGER ELECTRON SPECTROSCOPY -
0 ELECTRON HICR0 PROBE O ELECTRON SPECTROSCOPY FOR CHEMICAL ANALYSIS (ESCA) 0 BULK CHEMICAL ANALYSIS 0 SLUDGE ANALYSIS 0 TENSILE TEST 0 HUEY TEST .
RESULTS OF ANALYSIS 0F FRACTURE SURFACE ENERGY DISPERSIVE SPECTROSCOPY WEIGHT PERCENT)
Nr Cn FE Cu Ps ~ Sr CA INTERGRANULAR 55.59 13.93 14.52 2.36 4.87 1.58 0.78 REGION
. TENSILE 67.11 15.89 9.21 ----
0.42 1.19 ---- l OVERLOAD REGION ELECTRON MICR0 PROBE CROSS SECTION OF " TIGHT" CRACK - Nz, CR, FE, S i
i l
1 SCANNIN3 AUGER SPECTROSCOPY l
INTERGRANULAR REGION 0XIDE FIDI -- NI, CR, FE, S, NA, CL, K NI, CR AND FE PRESENT AS A MIXED HETAL OXIDE S -- 5 ATOMIC PERCENT PRESENT THROUGH OXIDE E CL -- 1 ATOMIC PERCENT PRESENT THROUGH 0XIDE NA, K -- PRESENT IN ISOLATED PARTICLES ON SURFACE -
': . , . l 9
ESCA DEPTH PROFILE ON MILLSTONE S/0 TUBE CRACK' e : : : : : : : : : : : : :
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)
l IMPLEMENTATION OF BORIC ACID TREA M ENT {
"NEW" CRACKS CONSISTENT WITH INITIAL CYCLE 9 OPERATION AND PROPAGATION OF INCIPIENT CRACKS WHILE ON BORIC ACID TREATHENT 0 INCIPIENT CRACKS FORMED DURING CYCLE 7 THROUGH 9 WILL CONTINUE TO PROPAGATE. DECREASING NUMBER OF CRACKS EXPECTED .
O BEHAVIOR OF EXISTING CRACKS IS ACCEPTABLE. CRACKS DO NOT APPEAR TO INCREASING CIRCUMFERENTIAL EXTEKT, ALTHOUGH LIGAMENTS BETWEEN INDIVIDUAL CRACKS MAY CORRODE, ALLOWING THE TUBE TO LEAK. LIGAMENT CORROSION SLOWER THAN THROUGHWALL PROPAGATION OF MICR0 CRACKS SUPPORTED BY L25/R19 0 OTHER FORMS OF CRACKING, SUCH AS FATIGUE, RULED OUT DEGRADED EGGCRATE TESTING FIBER OPTIC EXAMINATION REMOVED TUBE EXAMINATION
~
l CONCLUSIONS 0 CIRCUMFERENTIAL CRACKS ARE NOT A SAFETY CONCERN, SINCE POSTULATED CRACK BEHAVIOR SATISFIES " LEAK BEFORE BREAK" CRITERIA 0 HIGH LEVEL 0F CONFIDENCE THAT ALL EXISTING CRACKS HAVE BEEN IDENTIFIED AND REPAIRED 0 CORRECTIVE ACTIONS ARE EXPECTED TO HITIGATE FUTURE CRACKING 0 LOW LEAKAGE LIMIT PROVIDES ADDITIONAL ASSURANCE OF SAFE OPERATION l
l
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I O
STEAM GENERATOR TUBE STRUCTURAL CONSIDERATIONS i
6
MILLSTONE UNIT NO. 2 STEAM GENERATOP. TUBE INTEGRITY TUBE PLUGGING -
~
0 FOLLOWING THE EDDY CURRENT TEST DATA REVIEW, DEFECTIVE TUBES WERE PLUGGED.
O THE PLUGS USED WERE OF THE SAME HECHANICAL DESIGN WHICH HAS PREVIOUSLY BEEN INSTALLED AT MILLSTONE UNIT 2.
O A TOTAL OF 433 TUBES WERE PLUGGED. -
317 WERE STABILIZED AND PLUGGED SG1 SG2 TOTAL HL CL HL CL 159 106 39 13 265 52 317 0 THESAFETYkNALYSISBASEDPLUGGINGLIMITS WERE REVIEWED AND REMAIN VALID.
1
~
MILLSTONE UNIT NO. 2 _
STEAM GENERATOR TUBE INTEGRITY STRUCTURAL IMPLICATIONS OF CIRCUMFERENTIALLY CRACKED TUBES 0 SINCE THROUGH WALL CIRCUMFERENTIAL DEFECTS WERE NEW TO MILLSTONE UNIT N0. 2 IN 1987, )
TUBE STRUCTURAL INTEGRITY MEASURES WERE REVIEWED.
l 0 BECAUSE SUCH DEFECTS COULD SEVER A TUBE AND
-POTENTIALLY RESULT IN TUBE TO TUBE CONTACT, IDENTIFIED CRACKED TUBES WERE STABILIZED AND PLUGGED.
O THE STABILIZERS PREVENT TUBE TO TUBE CONTACT IF A TUBE SH0VLD BECOME SEVERED.
l
- _ - - - - - - -- l
. MILLSTONE UNIT N0. 2 '
STEAM GENERATOR TUBE INTEGRITY
~
.. O ALTHOUGH THE IDENTIFIED CRACKED TUBES ~HAVE .
BEEN PLUGGED AND POTENTIAL WEAR CONCERNS MITIGATED, ADDITIONAL DEFECTS OF THIS NATURE l WERE POSTULATED. STRUCTURAL IMPLICATIONS OF SUCH DEFECTS WERE THEN CONSIDERED.
O FRACTURE AND PLASTICITY CALCULATIONS WERE l
PERFORMED. IT WAS ESTIMATED THAT THE DEFECT IN TUBE R25L19 (1987 LEAK) WAS 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 TO BE 1.4 FOR ACCIDENT CONDITIONS (INCLUDING DYNAMIC EFFECTS) AND OVER 3 FOR NORMAL CONDI-TIONS. {
0 THESE MARGINS MEET THE REQUIREMENTS OF REGULATORY GUIDE 1.121.
0 0.10 GPM HAS BEEN ADOPTED AS THE MAXIMUM TECHNICAL SPECIFICATION ALLOWABLE LFAK RATE PER STEAM GENERATOR AT MILLSTONE UNIT NO. 2.
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 GPH. SINCE THIS IS LESS THAN THE 1.0 GPM l ASSUMED IN THE ACCIDENT ANALYSIS, IT IS l ACCEPTABLE.
~
I HILLSTONE UNIT NO. 2 ...
STEAM GENERATOR TUBE INTEGRITY ~
SUINARY ,
)
0 ALL OF THE TUBES WHICH HAD DEFECTS IN EXCESS OF THE TECHNICAL SPECIFICATION ALLOWABLE WERE PLUGGED.
O THE STRUCTURAL IMPLICATIONS OF THROUGH WALL CIRCUMFERENTIAL DEFECTS WERE-CONSIDERED.
0 -THE TUBES IDENTIFIED WITH CRACK INDICATIONS WERE STABILIZFD AND PLUGGED TO PREVENT POSTULATED WEAR FAILURES.
O CRACKED TUBES RETAIN ACCEPTABLE MARGINS AGAINST BURST.
O BY LIMITING PRIMARY-TO-SECONDARY LEAKAGE TO 0.10 GPM, ACCEPTABLE STRUCTURAL MARGINS ARE ASSURED FOR DEFECTS OF THIS TYPE.
0 WITH THESE MEASURES TAKEN, THE STRUCTURAL INTEGRITY OF THE STEAM GENERATORS IS ENSURED FOR THE CURRENT FUEL CYCLE.
_ i l
.. l PREVENTATIVE SLEEVING 1
{
0 PREVENTATIVE SLEEVING WAS SUGGESTED AS A POSSIBLE REPAIR OPTION. ,
1 D APPROXIMATELY 60% HOT LEG PROBLEM, SIGNIFICANT PROBLEM INSERTING SLEEVES q INTO HOT LEG TUBES.
2) LOW NUMBER OF DEFECTIVE TUBES VERSUS TOTAL POPULATION - 309/12,500.
O NOT COST OR ALARA EFFECTIVE e
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' Y sw e W
STEAM GENERATOR LEAK RATE MONITORING e
c.
LEAK RATE MONITORING e 0
~
TECHNICAL SPECIFICATION LEAK RATE LIMIT ; ~
0.1 GALLONS PER MINUTE (GPM) (144 GALLONS PER DAY)
THROUGH ANY ONE STEAM GENERATOR 0- LEAK DETECTION 0 STEAM JET AIR EJECTOR GASE0US RADIATION HONITOR 0 BLOWDOWN TANK EFFLUENT RADIATION MONITOR O PERIODIC " GRAB" SAMPLES STEAM GENERATOR BLOWDOWN (INDIVIDUAL)
STEAM JET AIR EJECTOR EFFLUENT 0 RADIATION HONITOR SETPOINTS ADJUSTED TO PROVIDE
" ALERT" ON INCREASING RADI0 ACTIVITY LEVELS j 0 IlEEDIATE GRAB SAMPLES TO DETERMINE LEAK RATE O PERIODIC FOLLOW-UP GRAB SAMPLES TO TREND LEAKAGE O ACTIONS ON ALERT - CHEMISTRY REP ON SHIFT 0 LEAK RATE MEASUREMENT p STEAM GENERATOR BLOWDOWN SAMPLES j
I i
i
~
LEAK RATE MONITORING (CON'T)
O LEAK RATE ANALYSIS AND REVIEW ;~
)
REVIEWED BY SHIFT SUPERVISOR FOR IMPACT ON TECHNICAL SPECIFICATION LIMITS ANALYSIS RESULTS REPORTED AND REVIEWED AT DAILY MANAGEMENT / STAFF HEETING l l
RESULTS OF " GRAB" SAMPLES TRENDED'HANUALLY 1
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- _ _- _ l ___ _ _ __
E-_ _ _ - - -
PRIOR EXPERIENCE 0 1987 TUBE LEAK - CAUSED BY CIRCUMFERENTIAL DEFECT SIMILAR TO THOSE FOUND IN 1989 EXAMINATION..
8 LEAK RATE LIMIT AT THAT TIME - 0.5 GPM O20 GPD) 0 INITIAL " ALERT" PROVIDED BY BLOWDOWN TANK EFFLUENT RADIATION MONITOR ALARM - CONFIRMED AT 0.08 GPM IN NO. 1 STEAM GENERATOR BY " GRAB" SAMPLES 0 INCREASE TO 0.15 GPM OVER 24 HOURS HONITORED BY PERIODIC SAMPLES OF NO. 1 STEAM GENERATOR BLOWDOWN
)
O LEAK RATE STABILIZED AT 0.15 GPM FOR ABOUT FOUR DAYS UNTIL PLANT SHUTDOWN - HONITORED BY PERIODIC SAMPLES OF STEAM GENERATOR BLOWDOWN.
CONCLUSION PRESENT LEAKAGE DETECTION AND LEAK RATE MONITORING PRACTICES, COUPLED WITH 0.1 GPM LEAK RATE LIMIT PROVIDE ASSURANCE THAT TUBE CRACKS WHICH GO THROUGH WALL WILL BE QUICKLY DETECTED AND ACTION TAKEN TO PREVENT TUBE RUPTURE. ,
eo me e e
es
I
(
I se 6
l.
h OVERALL CRACK ASSESSMENT e
W e
4 l
i j
1
s.
.y L CHEMISTRY a
O- POLISHER EFFLUENT IMPURITIES GREATLY REDUCED LATE IN CYCLE 7 )
0 BASIC ION IMBALANCE ACCOMPANIED IMPURITY REDUCTION 4
0 . LOCAL CAUSTIC FROM BASIC ION IMBALANCE, LATE .
CYCLE 7 TO EARLY CYCLE 9 {
'O BORIC ACID TREATHENT NEUTRALIZED CAUSTIC HOST OF- '
CYCLE 9 I
e.
t d.
WE O '27 CRACKS IDENTIFIED END OF CYCLE 8 0 309 CRACKS IDENTIFIED E00 9, Q WERE PRESENT EOC 8, BASED ON SAMPLE DATA 1
0 CIRCUMFERENTIAL CRACK EXTENT 140 T0 329 0 BY RPC "HACR0" MEASUREMENTS, 21 2 2500 ;
i
)
1
s CRACK PROCESS 0 SECONDARY SIDE STRESS CORROSION CRACKING 0 CORROSIVE SPECIES PROBABLY HA0H 0 STRESSES A RESULT OF PRIOR DENTIhG AND BUNDLE SHIFTING CRACK' MORPHOLOGY 0 SINGLE " MACR 0" CRACKS BY NDE ACTUALLY CLUSTER OF SEPARATE, SMALL "MICR0" CRACKS 0 MICR0 CRACKS IN DIFFERENT AXIAL PLANES AND SEPAR-ATED BY UNCRACKED METAL LIGAMENTS
w
,?.
CONCLUSIONS
~
0 CRACKS INITIATED FROM LATE IN CYCLE 7 TO EARLY
~ CYCLE 9 AS A RESULT OF CAUSTIC STRESS CORROSION CRACKING _ . .
O THE 309 CRACKS IDENTIFIED IN THE PRESENT INSPEC- '
. TION PRIMARILY A RESULT OF IMPROVED INSPECTION, BUT SOME COULD HAVE INITIATED EARLY IN CYCLE 9, <
. PRIOR TO BORIC ACID TREATMENT 0 CRACK INITIATION HINIMIZED OR ELIMINATED EARLY IN CYCLE 9 COINCIDENT WITH BORIC ACID TREATHENT 0 SMALL NUMBER OF INCIPIENT CRACKS COULD STILL EXIST BUT ALL SIGNIFICANT CRACKS IDENTIFIED AND' REPAIRED 0 INCIPIENT CRACKS, IF ANY, SHOULD PROPAGATE DURING CYCLE 10, BE IDENTIFIED BY NDE DURING THE END OF CYCLE 10 INSPECTION AND REPAIRED.
O NO FURTHER SIGNIFICANT CRACKING EXPECTED BEYOND CYCLE 10 i 0 IF INCIPIENT CRACK (S) PROPAGATE THROUGHWALL DURING i CYCLE 10, LEAKAGE WILL BE DETECTED PRIOR TO '
SIGNIFICANT STRUCTURAL DEGRADATION, ASSURING ORDERLY SHUTDOWN AND REPAIR IN ACCORDANCE WITH TECHNICAL SPECIFICATIONS l
I L
i 9
_m_m_ .-____ ,__ _ _ _ _ _ . _. . _ _ _ _ . _ _ _
MNO e :.
e o
M ^
k SUl4%RY l
l 4
<< t SUINARY 4
0 MILLSTONE 2CIRCUMFERENTIALCRACKSARENOT"A SAFETY CONCERN, SINCE POSTULATED CRACK liEH VIOR SATISFIED " LEAK BEFORE BREAK" CRITERIA 0 ALL SIGNIFICANT CRACKS HAVE BEEN IDENTIFIED AND REPAIRED O CORRECTIVE ACTIONS ARE EXPECTED TO MITIGATE FUTURE i CRACKING 0 LOW LEAKAGE LIMIT PROVIDES ADDITIONAL ASSURANCE OF SAFE OPERATION
. /
l s
l O
_ - - - - - - - - - - - - _ . _ - -

ML20245C138

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