ML20247A444
| ML20247A444 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 05/08/1989 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8905230147 | |
| Download: ML20247A444 (51) | |
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, I DUKE POWElt GoMem P.0, Hox 33189 CIIARLOTTE. N,0. 28242 lHALILTUCKER TE1.EPHONE vna enmement (704)373-4531 wimiaan enouwmum.
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May 8,.1989.
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- U. S. Nuclear' Regulatory Commission Attention: Document Control Desk Washington, D.C.
20555
Subject:
Duke Power Cen.pany McGuire' Nuclear Station Docket Nos. 50-369 and 50-370 i
- Attached-is a copy'of the McGuire 1 Nuclear power Station Evaluation of Tube
- l K
R18C25 and Justification for Return to power. This document was presented to the NRC staff in a meeting held in White Flint on May 5, 1989.
It contains the
.results of our evaluation and determination of the cause of the March 7, 1989 4 steam generator B tube rupture event on McGuire Unit 1.
l Summarizing from the abstract, as communicated to the.NRC staff on May 5, the
' document.provides the following. findings and conclusions of our investigation into the event.
c o
The cause of-the_ tube rupture was determined'to.be intergranular stress
- corrosion cracking on the outside diameter of the tube.
o The failed tube also contained a network of small axial and circumferential cracks linked together.
I The network of cracks is associated with, and confined.to, a linear o
Lsurface mark, which probably' occurred during the manufacturing process.
E o.
The failed tube had not been inspected since the baseline performed prior to Unit 1 operation.
o,
-If inspected, the degraded tube (R18C25) would have been discovered.
i o
Inspection of the other tubes in all four Unit 1 steam generators revealed no indications of detectable outside diameter stress corrosion cracking.
o Some local surface contamination appeared to be present within the stressed region of the aforementioned surface mark. This is felt to have been present at the time of initial service, providing the cause for the cracking to begin.
o Laboratory and field data suggest a crack propagation rate of approximately 0.7 mil / month.
o The rupture of tube R18C25 was a unique event.
{d 8905230147 890508 e
0 PDR ADOCK 05000369 P
PDC li A
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U..S. Nuclear Regulatory Commission Page Two May 8, 1989 o
McGuire Unit I steam generators can be operated for the remainder of of the current fuel cycle with no resulting unreviewed safety questions.
Our investigation into the steam generator tube failure and the preparation of the attached report was aided by Babcock & Wilcox, Westinghouse, and industry experts.
Also attached to this letter is a copy of the presentation material used at the May 5 meeting. This provides the status of the other items from the NRC's April 19, 1989 confirmation of action letter.
The tube plugs item is also addressed in the tube rupture evaluation and justification document as well. This information, along with my letter of April 26, 1989 and the conclusion of our meeting on May 5, completes the items in the confirmation of action letter.
As discussed with you on May 5, Duke Power will commit to perform 100% bobbin coil eddy current inspection on each of the McGuire Units' steam generators.
This will be done on the upcoming refueling outages for each unit.
Presently, Unit 2 is scheduled to begin on July 5, 1989 and Unit 1 is scheduled for early-mid 1990. We will communicate the results of each inspection to the NRC staff in reports and meetings prior to the restart from each refueling outage.
Finally, I would like to thank the NRC staff for its timely action in support of the McGuire Unit I restart effort.
Please let me, or the appropriate member of my staff, know of any further concerns you may have regarding this matter.
Very truly yours, g
H. B. Tucker JSW355/lcs xc: Mr. S. D. Ebneter Regional Administrator, RII U. S. Nuclear Regulatory Commission 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. P. K. VanDoorn NRC Resident Inspector McGuire Nuclear Station Mr. Darl Hood 1
l Office of Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission Washington, D.C.
20555 a
McGuire 1 Steam Generator Tube Integrity Meeting Presentation Materials Nuclear Regulatory Commission Rockville, Maryland May 5,1989 Duke Power Company I
_____.m__
AGENDA MAY 5, 1989 MEETING ON McGUIRE UNIT 1
]
STEAM GENERATOR TusE INTEGRITY INTRODUCTION TONY McCONNELL DUKE POWER i
CONFIRMATION OF TONY McCONNELL DUKE POWER ACTION LETTER STATUS STEAM GENERATOR CAROLL ROBINSON DUKE POWER TUBE PLUG INTEGRITY FIELD RELATED JOHN ESPOSITO WESTINGHOUSE ACTIONS FAILURE MECHANISM JIM BEGLEY WESTINGHOUSE l
JUSTIFICATION FOR SKIP HENDRIX DUKE POWER RETURN To POWER CLOSING REMARKS TONY McCONNELL DUKE POWER
e Completion of.
Confirmation of Action Letter Items 1)
Further meetings and reporting regarding the cause of tube failure and interpretation of these results into corrective actions.
Status Addressed in today's meeting
- 2) Eurther-meetings-regarding-t-ube-plugs Status Addressed in today's meeting 3)
Completion of procedur~e changes for entry conditions into Emergency Operating Procedures Status Provided by April 26, 1989 letter from H.B. Tucker to the NRC 4)
Completion of certain items from AIT report l
Status Miscellaneous procedure concerns addressed in April 26, 19 8 9 letter. Unmonitored release path concerns also addressed by Radiation Protection procedure changes and training.
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MCGUIRE UNIT 1 STEAM. GENERATOR PLUG INTEGRITY i
ALL MECHANICAL PLUGS IN SERVICE HAVE BEEN EVALUATED RELATIVE TO PLUG DESIGN, MATERIAL, AND CURRENT CONDITION CORRECTIVE ACTIONS HAVE BEEN TAKEN TO ASSURE THAT ALL INSTALLED PLUGS CAN SAFELY REMAIN IN SERVICE THROUGH THE REMAINDER OF THE FUEL CYCLE l
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STEAM GENERATOR TUBE PLUG INTEGRITY SOME B&W AND WESTINGHOUSE ALLOY 600 PLUGS o
HAVE EXPERIENCED PWSCC
- SOME HEATS OF MATERIAL HAVE LESS THAN IDEAL MICROSTRUCTURE
- INADEQUATE CARBIDE PRECIPITATION AT GRAIN BOUNDARIES
- MECHANICAL PLUGS AT GREATER RISK
- COLD LEG SERVICE LIFE MUCH LONGER THAN HOT LEG l
l i
MECHANICAL PLUGS WESTINGHOUSE PLUG TOP RELEASE EVENT AT NORTH ANNA MOsT SUSCEPTIBLE HEATS IDENTIFIED AS NX3962 AND NX3513 PWSCC ALSO IDENTIFIED IN PLUGS MANUFACTURED PROM HEAT NX4523 l
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n WESTINGHOUSE MECHANICAL PLUGS i
22 MECNANICAL PLUGS IN MCGUIRE UNIT 1 STEAM GENERATORS
+
20 IN SG A i
i 2 IN SG C INSTALLED 1982 - 1983 No MECHANICAL PLUGS INSTALLED IN MCGUIRE UNIT 1 MANUFACTURED FRoM HEATS NX3962, NX3513 oR NX4523 ALL. MECHANICAL PLUGS INSTALLED IN HCGUIRE UNIT 1
~ Frow MoST RESISTANT HEATS OF MATERIAL USED BY WESTINGHOUSE HEATS NX2386, NX2387 AND NX1989 u
~ MECHANICAL PLUGS IN SERVICE IN MCGUIRE UN T 1 I
NOT SUSCEPTIBLE To PLUG TOP RELEASE EVENi l
THROUGH END OF CURRENT CYCLE AND BEYOND.
l PROJECTED SERVICE LIFE FACTOR OF 16 GREATER l
THAN NX3962 AND NX3513 l
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MECHANICAL PLUGS 1
o B&W.
PWSCC IDENTIFIED IN ROLLED PLUGS REMOVED
'FROM V.C. SUMMER SUSCEPTIBLE HEAT IDENTIFIED As TELEDYNE W592-1 No IN-SERVICE FAILURES OF W592-1 PLUss i
J
3 B&W MECHANICAL PLUGS o
PRIOR To CURRENT OUTAGE 8 W592-1 RISBED PLUGS INSTALLED - 4 Hor LEG 156 W592-1 ROLLED PLUGS INSTALLED - 83 hot LEG ALL hot LEG W592-1 RIBBED PLUGS HAVE BEEN REMOVED FROM SERVICE ALL hot LEG W592-1 ROLLED PLUGS INSPECTED BY RPC TECHNOLOGY 6 OF 83 HAD INDICATIONS OF PWSCC IN HEEL ROLL TRANSITIONS 1 HAD OD INDICATION ALL 7 ROLLED PLUGS WITH INDICATIONS WERE REMOVED PROM SERVICE REMAINING W592-1 ROLLED PLUGS IN SERVICE IN MCGuIRE UNIT 1 Nor SUSCEPTIBLE To PLUG top RELEASE EVENT REMAINDER HAD No DETECTABLE DEFECTS NEVER DETECTED PWSCC IN TOE TRANSITION PWSCC IN toe TRANSITION WOULD RESULT IN LEAK BEFORE BREAK
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Tube Roll Plus Figure 10-1. B&W Roll Plug 9221M:1E-0503t9 10-12
i MCGUIRE UNIT 1 TUBE INTEGRITY VERIFICATION l
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ANALYSIS OF EXTENSIVE INSPECTION AND TUBE EXAMINATION RESULTS HAVE ESTABLISHED THAT THE R18C25 RUPTURE WAS A UNIQUE EVENT.
ALL TUBES WITH IDENTIFIABLE SIMILARITIES TO THE RUPTURED TUBE HAVE BEEN REMOVED FROM SERVICE.
THE DEGRADATION RATE DETERMINED FOR THIS EVENT IS SUCH THAT ANY POSTULATED DEFECT WILL NOT GROW TO SUCH AN EXTENT AS TO VIOLATE THE REQUIREMENTS OF REG. GUIDE 1.121 PRIOR TO THE END OF THE CURRENT FUEL CYCLE (10 MONTHS).
THE ACTIONS THAT HAVE BEEN TAKEN ASSURE THAT WE CAN OPERATE MCGUIRE UNIT 1 TO THE END OF THE CURRENT FUEL CYCLE.
~
FIELD RELATED ACTIONS
)
LEAK LOCATION IDENTIFICATION EDDY CURRENT TESTING ULTRASONIC TESTING VIDEO EXAMINATION TUBE PULL AND EXAMINATION REVIEW OF CHEMISTRY EXPERIENCE TUBE PLUGGING SPECIAL RPC TESTING
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EDDY CURRENT TESTING SHOWS-THAT R18C25 SG'B IS THE 0NLY TUBE WITH LENTIFIED OD CRACKING INDICATIONS SCOPE:
BOBBIN COIL - 100% FULL LENGTH - ALL STEAM GENERATORS ROTATING PANCAKE COIL
' CHARACTERIZATION OF ALL CLASSES OF BOBBIN COIL SIGNALS ROLL EXPANSION PWSCC TUBE WEAR:
PREHEATER, AVB, FOREIGN OBJECTS MANUFACTURING / INSTALLATION ARTIFACTS:
BUFF MARKS, PERMEABILITY
]
VARIATIONS, 1
INSTALLATION MARKS GENERAL INSPECTION IN THE REGION OF THE #20 BAFFLE PLATE IN SG B COLD LEG (27 TUBES) AND SG D COLD LEG (209 tubes)
SUPPLEMENTAL TESTING OF SG B TUBES (HEAT 3835) 117 HOT LEG TUBES 112 COLD LEG TUBES
RESULTS OF EDDY CURRENT TESTING i
BOBBIN COIL INDICATIONS OTHER THAN R18C25 CRACK WERE IN EXPECTED CATEGORIES AND LOCATIONS RPC CHARACTERIZATION CONFIRMED ABSENCE OF CRACK-LIKE INDICATIONS FOR VARIOUS CLASSES OF BOBBIN COIL SIGNALS NO INDICATIONS OF ODSCC WERE DISCOVERED IN EITHER THE #20 BAFFLE PLATE SAMPLES OR IN THE HEAT 3835 SUPPLEMENTAL PROGRAM I
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UTILITY:. DUKE POWER COMPANY PLANT: McGUIRE UNIT #1 i
i GEN: R$G B - COLD LEG - CRACK ORIENTATION DATE:
3/24/89 TIME:
4:15:33 ANALYST:
R9615' CHANNEL:. VERT FRE0lENCY. (KHZ): 258 RON: 18 COL: 25 PLRTE: SPEC 2RL M X I W tV3: 24.55 PHRSE 2 Hot *4TMD): las L2SS F1LL SCR.E 2158.8 Y COLO LEC L2SS PHRSE: 38 DEG HRX 2ND POSIfach):B.E7 LEAKER EXTENDS FROM THE 2BTH TSP + 0.4* TO - 3. S *.
(CIRCH LISEJ 31.5 YOLT S
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UTILITY: DUKE POWER COMPANY PLANT: MCGUIRE UNIT 1 GEN:
'"B" S/G COLD LEG
- DATE:
3/22/89 j
TIME:
5:25:33-ANALYST:.R9615 l
CHANNEL: VCPT FPEQUENCY (KHZ) ! 380 ROW: 13 COL t 3 4 PLRTE: SPE CIRL.
NRx IN0(v): !.53 PHREE IN0(%TWD):
14 LIEE FULL SCRLE 20.2 V 00 COLD LEG LI55 PHREE: 129 DEG HRx INO POSIinch): E.19 EIMILAR LOWER RMPLITUDE INDICRTION e 188 DEG.
[CIRCH LISS) 104.D YOLTS
- 2.)
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. RXIRL LENGTH-INCHE5 SB Rf*:LE-0CGREEE B
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ULTRASONIC TESTING IS CONSISTENT WITH EDDY CURRENT TESTING FOR VOLUMETRIC WALL LOSS RADIAL LONGITUDINAL BEAM SENSITIVE TO VOLUMETRIC TUBEWALL THICKNESS CHANGES SELECTED SAMPLE TO CORROBORATE EC RESULTS
7 IN-SITU VISUAL EXAMINATION SCOPE:
o ID OF TUBE R18C25 WITH WELCH ALLYN VIDEO PROBE o FIBERSCOPE EXAMINATION FROM TUBE LANE o REMOVAL OF ADJACENT TUBE R19C24 FOR FIBERSCOPE INSPECTION I
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IN-SITU VISUAL EXAMINATION I
RESULTS:
o IDENTIFIED AXIAL TUBE SPLIT AT AND BELOW BAFFLE PLATE-o OBSERVED DEPOSITS IN SURROUNDING AREAS OF MODERATE TO LIGHT QUANTITY o CREVICES OF MIXED OPEN AND PACKED APPEARANCE o WHITISH DEPOSITS OBSERVED CONCLUDED TO BE FROM LEAKAGE EVENT o DEPOSITS PREDATING THE LEAKAGE ARE NOT CONCLUDED TO BE OF SIGNIFICANCE IN THE TUBE DEGRADATION BASED ON PRESENT KNOWLEDGE I
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McGUIRE UNIT #1 SG B TUBES REMOVED FOR EXAMINATION Tuse BASIS R18C25 LEAKER (HEAT 3835)
R13C34 HEAT 3835 EXHIBITED EXTENDED EC SIGNAL R19C24 HEAT 3832 REMOVED TO PROVIDE SECONDARY SIDE VISUAL ACCESS To R18C25 1
i
MCGUIRE TUBE B (18-25)
^
PROPERTY OBSERVATIONS l
TENSILE PROPERTIES AGREE WITH MILL CERTIFICATION VALUES CHEMISTRY ANALYSES ARE IN SPECIFICATION WITH N0 UNUSUAL CONTAMINANTS PRESENT l
l
1 McGuire Tube B (18 - 25)
Deposits and EDS Analyses Layered Deposit on OD in and Away From Groove Inner Deposit is Thin (0.5-1.5 K m) and relatively chromium rich Outer Deposit is Thicker, iron-rich, Probably Normal AVT Magnetite No Lead, Sulfur, or Sodium Detected by EDS in Deposits Deposit Analyses Consistent with Well-Maintained AVT No Condenserin Leakage Species l
No Resin Throw Species 1
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i Chemistry Experience 1
McGuire 1 Chemistry Data was evaluated for the period of the past three fuel cycles Operating Chemistry Data, Chemistry Excursion Data and Wet Layup Chemistry Data Have Shown That Secondary Systems Chemistry Control Has Been Well Within EPRI Guidelines Hideout Return Data indicated That Crevice Chemistry Was Alkaline There Were No Significant Concerns identified Which Would Have Been Attributable to a Corrosion Condition in the McGuire 1B Steam Generator 1
McGuire Tube B (18 - 25)
Microstructure 4
Relatively Small Grain Size (ASTM 10)
Equiaxed Grains Predominantly intragranular Carbides (Dual Etch)
Carbide Banding Near ID Not Sensitized (Modified Huey Test)
Typical of Mill Annealed Tubing During McGuire Tube Production Era i
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1 MCGUIRE TUBE B (18-25)
METALL0 GRAPHIC OBSERVATIONS GROOVE = 0.66 MILS DEEP X 45 MILS WIDE UPSET, " SMEARED" METAL ~2 GRAINS DEEP AT EDGE OF GROOVE
'MICR0 HARDNESS EQUIVALENT TO 85 - 95 RB, HIGHER NEAR OD (GROOVE) AND ID, LOWER MID-WALL X-RAY RESIDUAL STRESS MEASUREMENTS INDICATE LOCAL TENSILE RESIDUAL STRESSES SLIGHTLY BELOW. YIELD STRENGTH
-LEVELS NO IGA; DISCRETE SCC ONLY RECENT OBSERVATIONS SHOW AN IRON AND CHROMIUM RICH REGION ON THE SURFACE OF THE GROOVE AWAY FROM THE CRACKED REGION
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- SHALLOW GROOVE j
SMALL CRACKS 0.3 IN.
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3.6 IN.
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18-9/16 IN.
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&'N FINE CRACKS A k UP s.s u
v B(18-25)
SECTION 3
1 MCGUIRE TUBE B(13-34)
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l o SAME HEAT AS DEGRADED TUBE B(18-25) o DEEP SCRATCHES PRESENT o NO CRACKS BY NDE o NO CRACKS IN BEND SPECIMEN AT DEEPEST CRACK o THREE BURST PRESSURE SPECIMENS SHOWED NO SCC o BURST PRESSURES (>12 KSI) NORMAL FOR DUCTILE PRESSURE OVERLOAD o 0XIDE MATERIALS SIMILAR TO THOSE ON B(18-25)
- o. TENSILE PROPERTIES AGREE WITH MILL CERTS o CHEMISTRY ANALYSES ARE IN SPECIFICATION WITH N0 UNUSUAL CONTAMINANTS PRESENT
9 MCGUIRE TUBE B (19-24)
NDE EXAMINATIONS COMPLETED VISUAL EDDY CURRENT RADIOGRAPHY RESULTS SHOW NO INDICATION OF TUBE DEGRADATION 1
i,
y NCGUIRE UNIT 1-
. PLUGGED. TUBE SUNNARY SG A SG B SG C SG D o
god.
(180)
(196)
(169).
.(228)
Tubes Plugged During
-March 1989 Outage
_o PWSCC within 11 12 12 6
'F* region.
7
-o Wear
^- Foreign.0bject.
3 o Stress Corrosion 1
Cracking (R18C25).
,o Manufacturing Artifacts.
- Free Span 4
5 4
13 Indications o Other Reasons
- Secondary-side 1
. access tc R18C25**
- Pulled tubes ***
2 Total' 15 '
24 16 19 Tubes
- Includes 114 Row I tubes preventively plugged in each steam generator.-
- ' Tubes R19C24 C** Tubes R18C25, R13C34 & R19C24 9239M:1E-0503a8 l
4 R__________________._______..____
l
SUMMARY
?
FIELD RELATED RESULTS TUBE' RUPTURE OCCURRED IN THE COLD LEG ON A STRAIGHT LENGTH (UNDEFORMED) IN AND NEAR THE #20 BAFFLE PLATE i
THERE WAS NO ADDITIONAL ODSCC DETECTED IN A i
J 100 %, FULL LENGTH INSPECTION 1
RPC PROBE INSPECTION CONFIRMED THE RESULTS l
0F THE BOBBIN COIL WITH RESPECT TO ODSCC
' VISUAL EXAMINATION OF THE DEPOSITS ON AND NEAR R18C25 DOES NOT SUGGEST THE PRESENCE OF A SIGNIFICANT STEAM BLANKETED REGION REVIEW OF THE OPERATING CHEMISTRY RECORDS INDICATES THE ABSENCE OF AGGRESSIVE CHEMICAL ENVIRONMENTS LABORATORY EXAMINATION CONFIRMED ODSCC IN A NARROWLY RESTRICTED AXIAL GROOVE ON R18C25 EXTENDED INSTALLATION MARKS ON R13C34 SHOWED NO EVIDENCE OF CRACKING ALL TUBES WITH INSTALLATION MARKS WERE PLUGGED
l GENERAL MECHANISM OF TUBE RUPTURE OF R18C25 HULTIPLE INITIATION OF OD STRESS CORROSION CRACKS IN A LONG SHALLOW SCRATCH OR GROOVE GROWTH OF CRACKS PARTIAL C0ALESCENCE OF CRACKS DEVELOPMENT OF LIMITED AREAS OF THROUGH WALL CRACKING l
DUCTILE OVERLOAD AND FRACTURE OF ID CRACK LIGAMENTS AND LIGAMENT BETWEEN CRACK SEGMENTS l
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ALL PREVIOUS EXPERIENCE WITH SCC ON THE OU DIAMETER OF ALLOY 600 STEAM GENERATOR T BEEN ASSOCIATED WITH OCCLUDED REGIONS AND CONCENTRATION OF AGGRESSIVE CHEMICAL SPECI l
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i UNIQUE ASPECTS OF TUBE R18C25 i
STRESS CORROSION OCCURRENCE
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l FREE SPAN CRACK INITIATION SITES ONLY CRACK LOCATION IS ON COLD LEG NO EDDY CURRENT EVIDENCE OF ANY OTHER SIMILAR CRACKING AFTER 100% B0BBIN COIL INSPECTION AND OVER 100 TUBE RPC INSPECTION 0F SAME HEAT {
AS CRACKED TUBE i
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THE 0CCURRENCE OF SCC DEPENDS ON:
ENVIRONMENT MATERIAL STRESS
CHEMICAL ENVIRONMENT CONSIDERATIONS FREE SPAN CRACKING INDICATES BULK SECONDARY WATER CHEMISTRY IS THE ENVIRONMENT OF INTEREST.
CONCENTRATION OF CHEMICAL SPECIES NOT LIKELY IN ABSENCE OF OCCLUDED REGIONS EXPERIENCE WITH SCC IN A BULK WATER ENVIRONMENT IS ESSENTIALLY LIMITED TO PRIMARY
- WATER SCC PRIMARY WATER IS CONSIDERED TO BE MORE AGGRESSIVE WITH RESPECT TO SCC THAN SECONDARY 1
WATER DUE TO LI, 8 AND H ADDITIONS e
-__._____________.__.m___
?
1 CONSIDERATION OF MATERIAL SUSCEPTIBILITY TO STRESS CORROSION CRACKING METALLURGICAL STRUCTURE AND PROPERTIES WITHIN
. EXPECTED BOUNDS FOR MILL ANNEALED ALLOY 600 TUBING i
FINE GRAIN SIZE, HIGH YIELD STRENGTH, AND 0.04% C INDICATE TUBE R18C25 HAS A SIGNIFICANT SUSCEPTIBILITY TO PWSCC, BUT WITHIN EXPECTATIONS FOR MILL ANNEALED ALLOY 600 LABORATORY TEST RESULTS ON MILL ANNEALED ALLOY 600 INDICATE OD MORE RESISTANT TO SCC THAN ID
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MECHANICAL LOADING
' CONSIDERATIONS SCRATCH PROVIDES
-- LOCALIZED PLASTIC DEFORMATION
- LOCALIZED RESIDUAL STRESSES
- DISTURBANCE OF POLISHED OD SURFACE
- OPPORTUNITY FOR MULTIPLE ALIGNED CRACK INITIATION SITES PRESSURE DIFFERENTIAL HOOP STRESS IS 12 KSI A SCRATCH IS NOT MECHANICALLY EQUIVALENT TO ANY KNOWN PWSCC SITE
EXTRAPOLATION OF PRIMARY SIDE SCC EXPERIENCE TO COLD LEG CRACKING ON THE SECONDARY SIDE
' TEMPERATURE HOT LEG PWSCC PRECEDES COLD LEG EFFECT.
BY A FACTOR OF FOUR OR MORE.
DUKE POWER EXPERIENCE INDICATES FOUR IS A REASONABLE CHOICE MECHANICAL REGIONS WITH SUBSTANTIAL GENERAL LOADING PLASTIC DEFORMATION ARE AFFECTED REQUIRED FOR U BEND TANGENT POINTS CRACKING SKIP ROLLS ROLL TRANSITIONS, DENTED TUBE SUPPORT PLATE INTERSECTIONS 1
~
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A SCRATCH I3 CONSIDERED A NECESSARY BUT NOT SUFFICIENT CAUSE FOR THE CRACKING OF TUBE R18C25 IN A BULK SECONDARY SIDE ~ WATER COLD LEG ENVIRONMENT l
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ADDITIONAL CRACK INITIATION CONSIDERATIONS
- SINCE A SCRATCH EXPOSED TO COLD LEG BULK SECONDARY WATER IS NOT CONSIDERED A SUFFICIENT CAUSE FOR CRACKING, ANOTHER FACTOR MUST BE CONSIDERED
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- THE PRESENCE OF BOTH AXIAL AND CIRCUMFERENTIAL CRACK INITIATION SITES POINTS TO THE ACTION OF AN-AGGRESSIVE ENVIRONMENT
- ABSENCE OF OCCLUDED REGIONS IN FREE SPAN CRACK INITIATION SITES ARGUES AGAINST
{
CONCENTRATION OF CHEMICAL SPECIES (AS DOES ABSENCE OF OTHER CRACK INDICATIONS, ESPECIALLY ON THE HOT LEG)
- A START OF SERVICE CONTAMINANT ON THE TUBE SURFACE PROVIDES FOR CRACK INITIATION BUT NO LONG TERM EFFECT ON GROWTH L
CRACK GROWTH CONSIDERATIONS ROI LEG PRIMARY SIDE CRACK GROWTH RATE = 4 TO 6 MILS / MONTH
{
BEST ESTIMATED ACTIVATION ENERGY FOR CRACK
~ GROWTH RATES IS 33 KCAL/MOL EXTRAPOLATED PRIMARY SIDE COLD LEG CRACK GROWTH RATE = 1 TO 1.5 MILS / MONTH SECONDARY SIDE COLD LEG CRACK GROWTH RATE SHOULD BE LESS THAN PRIMARY SIDE
. CRACK GROWTH OBSERVED FOR TUBE R18C25 = 0.7 MILS / MONTH l
1 1
J
.1 BEST EXPLANATION OF CRACKING MECHANISM CONSISTENT WITH:
1 PULLED TUBE EVIDENCE PLANT OPERATING HISTORY NDE INSPECTION'RESULTS i
GENERAL FIELD AND LABORATORY EXPERIENCE WITH SCC BENAVIOR OF ALLOY 600 CRACK INITIATION -
COMBINED ACTION OF SCRATCH, APPLIED STRESSES AND A LOCAL CONTAMINANT ON TUBE SURFACE AT STAltT OF SERVICE CRACK GROWTH DUE TO APPLIED STRESSES, AND ACTION OF BULK SECONDARY SIDE WATER ENVIRONMENT
w-MCGUIRE-UNIT 1 TUBE INTEGRITY VERIFICATION ANALYSIS OF EXTENSIVE INSPECTION AND TUBE EXAMINATION RESULTS.HAVE ESTABLISHED THAT THE R18C25 RUPTURE WAS A UNIQUE EVENT.
ALL TUBES WITH IDENTIFIABLE SIMILARITIES TO THE RUPTURED TUBE HAVE BEEN REMOVED FROM SERVICE.
l THE DEGRADATION RATE DETERMINED FOR THIS EVENT IS SUCH THAT ANY POSTULATED DEFECT WILL NOT GROW TO SUCH AN EXTENT AS TO VIOLATE THE REQUIREMENTS OF REG.
GUIDE 1.121 PRIOR TO THE END OF THE CURRENT FUEL CYCLE (10. MONTHS).
LEAK-BEFORE-BREAK BASIS HAS BEEN ENHANCED BY PLUGGING OF TUBES WITH EVIDENCE OF LINEAR INDICATIONS ON-G0ING AND FUTURE ACTIVITIES WILL SUPPORT LONG TERM UNDERSTANDING AND SAFETY BASIS 4
i
OBSERVATIONS SUPPORTING THE UNIQUE NATURE 0F l
TUBE R18C25 o
EXTENSIVE EDDY-CURRENT SHOWED NO ADDITIONAL DEFECTS SIMILAR TO R18C25 100% BOBBIN COIL
' SELECTED ROTATING PANCAKE COIL (RPC) EXAMINATIONS o
ABSENCE OF INDICATIONS SIMILAR TO R18C25 ANYWHERE IN THE MCGUIRE 1 STEAM GENERATORS SHOWS THAT WIDE SPREAD DEGRADATION IS UNLIKELY o
COMPARISON OF CURRENT OUTAGE EDDY CURRENT RESULTS WITH PREVIOUS RESULTS SHOWS NO SIGNIFICANT CHANGES o
INDICATIONS SIMILAR TO R13C34 CAN BE DETECTED AND SHOW NO EVIDENCE OF CRACKING WHEN EXAMINED WITH RPC o
ALL TUBES WITH GROOVE LIKE INDICATIONS WERE CONSERVATIVELY PLUGGED o
LABORATORY EXAMINATIONS OF R13C34 SHOWED NO CRACKING
DEGRADATION GROWTH RATE WILL NOT RESULT IN TUBE RUPTURE PRIOR TO END OF CURRENT CYCLE o
INDUSTRY AND MCGUIRE UNIT 1 EXPERIENCE SUPPORTS RELATIVELY SLOW GROWTH RATE FOR COLD LEG STRESS CORROSION CRACKING o
0.7 MILS PER MONTH CRACK GROWTH PREDICTED
ENDLOF CYCLE. PREDICTED CRACK DEPTH NORMAL ACCIDENT OPERATIONS CONDITIONS POSTULATED INITIAL CRACK. DEPTH 49%
49%
ESTIMATED CRACK 3
GROWTH
- 16%
16%
PREDICTED CRACK DEPTH **
65%
65%
MAXIMUM ALLOWABLE CRACK DEPTH PER REG. GUIDE 1.121 65%
67%
- ASSUMES LIMIT OF DETECTABILITY OF 50% THROUGH WALL
- o 10 MONTHS AT 0.7 MILS PER MONTH
h..
i LEAK-BEFORE~ BREAK ATTRIBUTE BASED TUBE PLUGGING ENHANCES o
LEAK-BEFORE-BREAK PROBABILITY CRACKING WHICH CAUSED R18C25 RUPTURE ASSOCIATED WITH LINEAR INDICATION IDENTIFICATION AND PLUGGING OF TUBES WITH LINEAR INDICATIONS INCLUDED IN THE INSPECTION PLAN l
REMOVAL FROM SERVICE WAS BASED ON i
LINEAR ATTRIBUTE INDEPENDENT OF THROUGH WALL DEPT!i L
TUBES WITH DETECTABLE LINEAR INDICATIONS HAVING LENGTHS EXCEEDING THOSE REQUIRED FOR UNSTABLE CRACK GROWTH WERE REMOVED FROM SERVICE 1
USE OF IN PLANT LEAK MONITORING POLICY CONSISTENT WITH NRC BULLETIN 88-02 PROVIDES ADDITIONAL LEAK-BEFORE-BREAK MARGIN l
)
)
o FUTURE ACTIVITIES l
l o
100% BOBBIN COIL INSPECTION MCGUIRE UNIT 2 STEAM GENERATORS, JULY 1989 i
o 100% B0BBIN COIL INSPECTION MCGUIRE i
UNIT 1 STEAM GENERATORS, 1990 i
o EVALUATE NDE METHODS FOR IMPROVED DETECTION / CHARACTERIZATION OF THE R18C25 CONDITION
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