ML18038B047
| ML18038B047 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/18/1994 |
| From: | Salas P TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-94-03, GL-94-3, TAC-M90082, NUDOCS 9411300170 | |
| Download: ML18038B047 (36) | |
Text
PH.IC3R.I EY
,ACCELERATED RIDS PROCESSING REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSIO52 NBR:9411300170 DOC.DATE 94/11/18 NOTARIZED: YES DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH'.NAME AUTHOR AFFILIATION SALAS,P.
'Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Forwards results of Unit 2 core shroud insp committed to in util 940823 response to GL 94-03.
DISTRIBUTION CODE D030D COPIES RECEIVED LTR ENCL SIZE:
TITLE: TVA Facilities Routine Correspondence NOTES
,R RECIPIENT ID CODE/NAME PD2-4 INTERNAL: ACRS NRR/DSSA RES/DE/SSEB/SES COPIES RECIPIENT LTTR ENCL ID CODE/NAME-1 1
WILLIAMS,J.
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1 COPIES LTTR ENCL 1
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1 NRC PDR D
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NOTE TO ALL"RIDS'ECIPIENTS:
PLEASE HELP US TO REDUCE lVASTE!CONTACTTHE DOCUb!ENTCONTROL DESK, ROOM Pl-37 (EXT. 504-2083 ) TO ELIXIINATEYOUR NAME FROII DISTRIBUTIONLISTS I'OR DOCLMENTS YOU DON"I'L'ED!
TOTAL NUMBER OF COPIES REQUIRED:
LTTR 14 ENCL 13
4l 4
Tennessee Valley Authority. Post Office Box 2000. Decatur. Alabama 35609 November 18, 1994 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Tennessee Valley Authority
)
Docket No. 50-260 BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 2 RESULTS OF CORE SHROUD INSPECTION (TAC NO. M90082)
This letter provides the results of the Unit 2 core shroud inspection committed to in TVA's August 23,
- 1994, response to Generic Letter (GL) 94-03, "Intergranular Stress Corrosion Cracking (IGSCC) of Shrouds in Boiling Water Reactors."
The inspection was performed during the Unit 2 Cycle 7 refueling outage and completed on October 22, 1994.
The results of the inspection indicate that severe core shroud cracking is not occurring in Unit 2.
Minor surface connected planar indications were found on three welds.
No through wall cracks were identified.
The inspection results were obtained by qualified personnel using the best available technology.
TVA performed non-destructive examinations (NDE) of 100< of the accessible areas on the horizontal welds using the GE Smart-2000 system and suction cup scanners.
An enhanced video system (Westinghouse 1250 camera) was used in selected areas to look for obstructions and assist in setting up ultrasonic test equipment.
TVA evaluated the Unit 2 inspection results and determined that. Unit 2 can safely be returned to service and operated for at least two additional operating cycles without repairs.
The analysis indicates that postulated crack growth during the next two operating cycles will be less than the safety criteria established by General Electric (GE) and the Boiling Water Reactors Owners Group (BWROG)
(GE NE-523-A107P-0794 and BWROG letters to NRC dated July 13 and 14, 1994).
TVA's analysis used conservative
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U..S. Nuclear Regulatory Commission Page 2
November 18, 1994 assumptions for such factors as crack growth and uncertainties in the amount of cracking identified.
Summaries of the inspection results and TVA's safety analysis that supports restart and operation of the Unit 2 core shroud are provided in the enclosure.
TVA is continuing to work with the BWROG and GE to develop acceptable repair methodologies when repair becomes necessary, and develop inspection plans for conducting weld examinations on the remaining core shroud welds.
TVA will keep NRC informed about future repair and inspection activities as information becomes available and plans are finalized.
There are no commitments contained in this letter.
Xf you have any question please telephone me at (205) 729-2636.
Si Salas Site Licensing Manager Subscribed and sworn to before me this
(%$4 day of Ql~1~1994.
Notary Public My Commission Expires Commlsslnn Expires 10l06/SS Enclosure cc:
see page 2
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U.S. Nuclear Regulatory Commission Page 3.
November 18, 1994 Enclosure cc (Enclosure):,
Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Mark S. Lesser, Section Chief U.S. Nuclear Regulatory Commission Region. II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry, Nuclear Plant Route 12, Box 637
- Athens, Alabama 35611 Mr. J.
F. Williams, Project Manager U.S. Nuclear Regulatory, Commission One White Flint, North 11555. Rockville Pike Rockville, Maryland 20852
4l:
ENCLOSURE TENNESSEE. VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 2 BFN UNZT 2 REACTOR CORE SHROUD ZNSPECTZON RESULTS AND ANALYSZS I'ACKGROUND Intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) internals has been identified as a
technical issue of concern by NRC and the nuclear industry.
TVA has been fully aware of IGSCC concerns in the core shroud and has been working closely with General Electric (GE) and the Boiling Water Reactor Owners Group (BWROG) to address this issue.
As a result of the.IGSCC concerns, NRC issued Generic Letter (GL) 94-03, "Intergranular Stress Corrosion Cracking (IGSCC) of Shrouds in Boiling Water Reactors,"
on July 24, 1994.
Among other things in the GL, NRC requested that BWR licensees inspect their core shrouds for cracking at the next scheduled refueling outage and
,provide the inspection results within 30 days of completing the. inspection.
In response to the GL (TVA letter to NRC dated August 23, 1994),
TVA committed to inspect 1004 of the accessible areas on welds Hl through H7 (see Figure E-1) using the best available non-destructive examination (NDE) technology.
The inspections were performed during the BFN Unit 2 Cycle 7 refueling outage that began on October 1,
1994.
In addition, TVA's response provided details about the construction of the BFN core shrouds and. discussed the risk factors that affect BFN.
II+
INSPECTION
SUMMARY
TVA and GE'nspected 100> of the accessible areas on the Unit 2 core shroud welds Hl through H7 using NDE methods.
The inspections were completed on October 22, 1994.
The inspections were performed by qualified personnel using the best available technology in accordance with approved BFN procedures.
The full inspection report is available on-site for review.
FIGURE E-1 BFN CORE SHROUD CONSTRUCTION DETAILS shroud Head i-lange vs V
H-i l
Top Guide "uppor t Ring
-(
0 O
O 41 i~-4 H-5 Core Plate Support Ring
'p Zhr oud vocor ~
P(axe Shr oud Suppor'eg Q-l i E-2
Personnel performing the examinations were certified to at least Level II status in accordance with.SNT-TC-1A, 1984 Edition.
Additionally, personnel performing ultrasonic (UT) examinations were qualified through the Electric Power Research Institute (EPRI)
NDE Center in accordance with the Coordination Plan for NRC/EPRI/BWROG Training and Qualification Activities of NDE Personnel.
Ultrasonic examinations (UT) were performed using the GE Smart-2000 system and suction cup scanners.
UT was performed on 1004 of the accessible areas on all seven welds.
Visual examinations were performed in selected areas to locate obstructions and assist in setting up ultrasonic test equipment.
Inspection procedures were prepared to implement the applicable portions of ASME Section V and XI recommendations, the NRC/EPRI/BWROG Coordination Plan, and General, Electric (GE) Service Information Letter (SIL)-
572.
The inspection procedures were approved by TVA.
Accessibility for the inspections was limited due to various equipment or internal structures that restrict access to the welds.
The proximity of various components such as guide pins, lifting lugs, core spray downcomers, shroud, head locking lugs, jet pump riser braces, and jet pumps precluded further examination.
Figure E-2 shows a
"roll-out" of the areas inspected.
The following provides a summary overview of the amount of each weld TVA examined:
WELD NUMBER CIRCUMFERENCE EXAMINED INCHES PERCENTAGE EXAMINED H1 H2 H3 H4 H5 H6 H7 230.50" 438.95" 415.14" 401.60" 401.60" 21.00" 14.00" 33.354 63.514 63.804 61.72%
61.72%
3.334 2.224 The amount of examination coverage for welds H1 through H5 varied from that achieved during the BFN Unit 3 shroud inspection.
Specifically, coverage for welds H1 through H4 was 5 to 20 percent less while coverage for H5 was 20 percent more than that achieved on Unit 3.
These. variances from Unit 3 are attributed to the relative difference in location of the interferences's
,encountered on the Unit 2 shroud.
The amount of coverage for welds H6 and H7 was 1 to 2 percent less than that achieved on Unit 3.
This variance is attributed to the amount of weld buildup encountered on the H7 weld and the size of the transducer package utilized on the H6 weld.
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III INSPECTION RESULTS The results of the Unit 2 inspection indicate that severe cracking of the core shroud welds is not occurring.
During UT inspections, surface connected planar indications were found in three welds (H2, H3, and H5).
The flaws were dispersed around the circumference of each weld.
There were no through-wall cracks identified.
A summary of the Unit 2 inspection results is provided below.
The individual Examination Summary Sheets for shroud welds H1 through H7 are provided on pages E-6
,through E-12.
WELD NUMBER INSPECTION TYPE RESULTS FLAW TYPE Hl UT No reportable indications N/A H2 H3 UT UT (1) indication 1.34" total length (3) indications 9.41" total length Planar Planar (3)
H4 UT No-reportable indications N/A H5
'UT (6) indications 9.09" total length Planar (6)
H6 UT No reportable indications N/A H7 UT No reportable indications N/A E-5
EXAMINATION
SUMMARY
SHEET GE Nuclear Energy REPORT NO.:
MKQ3 PROJECT:
1 W
PROCEDURE REV~ FRR:~
SYSTEM:
WELD NO.:
CONFIGURATION'EV~
FRR:~
REVQll8. FRR:~
EXAMINER:
EXAMINER:
EXAMINER:
DATASHEET NO.(S):
LEVEL:
~
LEVEL:~l LEVEL'~~> I DMT QPT Svr Qvr Q CIRCUMFERENTIAL D>>
j CAL SHEET NO.(S):
Dunng the examination of the above referenced weld. no surface connected planar flaws or any indications associated with IGscc IIAscc were recorded by the Smart 2000 system utilizing45'hear wave. 60'efracted longitudinal wave. and OD creeping wave search units.
The 45'hear wave search unit did record non~levant indications from both sides of the weld, along with inside and outside surface weld crown geometry, acousuc interface. and insxte surface geometry from the lower side of the weld.
The 60'L search unit recorded non-relevant indicauons from both sides of the weld. along with inside surface weld crown geometry from the upper side of the weld.
The OD creeping wave search unit recorded only no~levant indications from both sides of the weld.
Th's examination was also limited to L"dimensions of 13'o 17'. 21'o 25. 28 to 32', 36'o 40', 43'o 47', 51'o 55', 58'to 62', 66'o 70',
73'o 77', 81
!o 85' 88'o 92'. 96'o 100. 103'o 107'. 111 to 115. 118'o 122. 126 to 130'. 133'o 137, 141 to 145', 14&'o 152, 261 to 265'. 268'o 272'. 276 to 280', 283'o 287'. 291 to 295'. 298'o 302'. 306 to 310'. 313 to 317'. 321'o 325'. 328'o 332'. and 336 to340 fromvessel "0" duetotheoroximityofliftinganavibrationtugs.topguidepins.andcorespraydowncomers.
Circumferential L dimensions for all examination scans were recorded in angular uncs in lieu of linear units. The conversion factor forcircumferential measurements is 1.92" per degree.
SUM Y
~OI~ ~
LEVEL DATE
~~>
~ ~H 1
LEVEL DATE ANNREVIEW
/o DATE PAG~OF:~
4l I
EXAMINATION
SUMMARY
SHEET GE Nuclear Energy REPORT NO.:
~ZRE92 PROJECT' W
PROCEDURE'RV~
FRR:~
SYSTEM:
WELD NO.:
REF~ FRR:~
CONFIGURATION'RF~FRR:~
EXAMINER'XAMINER:
EXAMINER:
LEVEL':
LEVEL:
LEVEL:~FI Q CIRCUMFERENTIAL 0 LONGITUDINAL 0 OTHER
'DATASHEET NO.(S)
CALSHEET NO.(S):
During the ultrasonic examination of the above referenced west. one (1) inside surface connected planar flaw indication was recorded by the Smart 2000 system utilizing45 shear wave. 60 refracted longaudinal wave, and OD creeping wave search units. This lndicadan has the foilovnng parameters:
Indication Numoer Distance From Lo Total Length'emaining Ligament Thruwaii Side of Type Search Dimension Weld Reflector Unit 1
72.6' 139.4 0.7F I 1.34" 1.82"
.18" Lower Planar 45'ength sizing for indications was determined as the point where the indication signal response was obscured bythe baseline noise.
The throughwall dimcnsian for caen inaicauon was aetermmcd with the tip diffraction technique using the absolute amval time sizmg method.
The 45'hear also recorded non-relevant indications. msiae surface geometry, and inside surface weld crown geometry fram both sides of the weld along with acoustic interface. outside surface weld crown geometry, and the one (1) previously referenced planar flawflam the upper side of the weld.
The 60'RL also recorded norweicvant indications. inside surface geometry, and inside surface weld crown geometry fram both sides of the weld along with shear component and acausuc interface fram tne upper side of the weld.
The OD creeping wave search unit recorded only norweicvant indications from both sides of the weld.
This examination was limited to L dimensions of 12 to 157'nd 260 to 343'rom vessel'0'due to the proximity of liltingand vibration lugs, top guide pins, and carespray downcomers.
Circumfcrenual L"dimensions for all exammahon scans were recorded in angular units in lieu af linear units. The conversion factor for circumferential measurements is 1'.92" per degree.
SU,S GE
~IO I Fi4 LEVEL.
DATE LEVEL DATE tjTIUTVREVtav I t4/n, ANIIREVIEW r%~/F~
DATE DATE PAG~OF:~
E-7
GE Nuclear Energy EXAMINATtON
SUMMARY
SHP~
REPORT NO.
PROJECT:
W PROCEDURE'RV~
FRlL~
SYSTEM:
WELDNO.'ONFIGURATION'RF~
FRlL~
RRV~ FRR:~
EXAMINER:
EXAMINER EXAMINER:
LEVEL:
LEVEL:~
LEVEL:~
WELD TYPE:
PMT PPT 5 UT P VT P CIRCUMFERENTlAL P LONGlTUDINAL 0 OTHER~QQQ DATASHEET NO.(S):
CALSHEET NO.(S):
0unng the ultrasonic examination of the above referenced weld. three (3) inside surface connected planar flaw indications were recorded by the Sman 2000 system utilizing 45 shear wave. 60'efracted longitudinal wave. and OD creeping wave search units. These indicabons have the followingparameters:
Indication Number Distance From Lo Total Length Remaining Ligament ThruwaN Side of Dimension Weld Type Reflector 60.7' 110.4" 270.0'488.7 331.6' 6002 1.30' 1.35 1.50' 2.72" 2.40' 4.34 1.56" 1.45" 1.22"
.44 < 50% TW Lower
.55
< 50% TW Lower
.78
( See note )
Lower Planar Phtnar Phtnar 45 I60 45 I60'5'I60 Length sizing for indications was determined as the point where the indication signal response was obscured by the baseline noise The throughwall dimension for each indication was determined with the tip diffraction technique using the absolute amval time sizing method.
Note: Thruwatl dimension on indicauon ¹3 was determined from the tip signal response which exhibited the most through waN dimension.
However. due to the outside surface weld crown geometry the fullecho dynamic pattern from the tip signal response could not be acnieved and should be considered a best effort sizing estimation.
The 45'hear also recorded no~levant indications. beam redirect. inside surface geomeuy, and inside surface weld crown geometry akeg with the three (3) previously referenced planar flaws from the lower side of the weld.
The 60 RL also recorded norwetevant indications along with shear component and inside surface geometry from the weld crown, as wei as the three (3) previously referenced planar flaws from the lower side of the weld.
The OD aeeping wave search unit recorded only norwelevant indications from the lower side of the weld.
No examination was performed from the upper side of the weld due to the component conflgurathn. This examination waa Smited to L dimensionsof13 to157 and 260 to344'fromvesser'0'duetotheproximityofliftingandvibrationluga.topguidepins,andcorespray downcomers.
Circumferential L"dimensions for all examinauon scans were recorded in angular units in lieu of linear unCs. The conversion factor for arcumferenual measurements is 1.81" per degree.
~
~O.
WAAR LEVEL DATE Ii aallARY Y
ER BY LEVEL
&TE UTlLrTYRENEW 4I'a ANu REVIEW DATE DATE PAG~OF:~
E-8
Ol
GE Nuclear Energy EXAMINATIONl
SUMMARY
SHEET REPORT NO.
P.ROJECT:
1 W
PROCEDURE'EV~
FllR:~
SYSTEM WELD NO.:
CONFIGURATION'EV~
FRR;~
REV~ RllL~
EXAMINER:
EXAMINER:
EXAMINER:
DATASHEET NO.(S):
LEVEL:
LEVEL:~
LEVEL:~
QMT QPT OUT QVT G CIRCUMFERENTIAL Q LONGITUDINAL 8 OTHERAHBOllQ CALSHEET NO.(S):
Dunng the exammauon of the above referenced weld. no surface connected planar flaws or any indications associated with IGscc / IAscc wei recorded by the Smart 2000 system utilizing45'hear wave,'0'efracted longitudinal wave, and OD creeping wave search uiuts.
The 45'hear wave search unit did record norwelevant indications and inside surface weld crown geometry from both skfes of the weld, along wkh beam redirect and outside surface weld crown geometry from the upper side.
and welding discontinuities from the kwer side of the weld.
The 60 RL search unit recorded nonwelevant indications. acoustic interface. and shear component from both sides of the wekf, along with hsid surface weld crown geoinetry from the upper side, and welding discontinuides from the lower aide of the weld.
The OD creeping wave search unit recorded only norHelevant indications from both sides of the weld.
This examination was also limited to L dimensions of 12",o 157'nd 267 to 344'rom Vessel 0
due to the proximityof IUng and vibraflon lugs. top guide pins.'and core spray downcomers.
Circumferential "L"dimensions for all examination scans were recorded in angular units in lie of linear unrts. The conversion factor forcircumferential measurements is 1.61 per degree.
5UlBCARY Y
~~, I~OI R 4 LEVEL DATE F rA4F DATE G+REtrtEOE$ 4W LEVEL DATE g/
ANIIREVlEW E-9 4/A DATE PAG~OFt~
~~~WV.~
I 4l
EXAMINATlON
SUMMARY
SHEET GE Nuclear Energy REPORT NO.
~~5 PROJECT' W
PROCEDURE'EV~
FIDE~
SYSTEM:
WELD NO.:
REY~ ERIE~
CONRGVRATION'EY~ERIE~
EXAMINER:
EXAMINER:
EXAMINER:
LEVEL:
LEVEL:~
WElD TYPE:
C!Mr OPT 0 Ur Elvr C3 CIRCUMFERENTIAL Q LONGITUDINAL 0 OTHER&haQUD.
DATASHEET NO.(S):
CAL'SHEET NO.(S):
During the ultrasonic examinatian of the above ratarenced weld, six (6) inside surface connected planar flaw indicadons were recorded by the smart 2000 system uuiizing 45'hear wave,'60'efracted Iongnudinal wave. and oD creeping wave search units. These indicatens have tha faliovnng parameters:
Indication Number Distance From Lo Total L'ength'emaining Ligament TIIruwail Side of Type Search Dimension Weld Re6actor Unit 71.4' 129.2 101.7' 184.'I'03.4' 187.2 150.9' 273.1" 335.2' 605.7" 337.2' 610.3 1.10' 1.99
.90' 1.63"
.60' 1.09 1.60' 2.90
.51'/
.92
.31' 1.16" 1.04" 1.13 1.26" 1.89 1.78"
.84" <<50% TW
.96" ( See note )
.87 <<50%TW
.74" <<50% TW
.11" <<50% TW
.22 <<50%TW Upper Planar 45'/60 Upper Planar 45'/60 Upper Planar 45'/60 Upper Planar 45 /60 Upper Planar 45'pper Planar 45'.ength sizing for indications was dateimined as the pomt where the indication signal response was obscured by the baseline noise.
The througnwall dimension for each indication was aateimined with the tip diffraction technique using the absolute amval time sizing matnod.
Note: Thruwall dimension on indication ¹2 was determined from the tip signai response which exhibited the meat through wall dimension.
However. dua to the outside surface weld crown geometry the fullecho dynamic pattern from the tip signal response could not be achieved and should ba considered a best effort sizing estimation.
The 45'hear also recorded no~levant indications. beam redirect. inside surface weld crawn geometry, and weld discontinuities from beth sides of,the weld along with beam redirect. inside surface geometry, and outside surface weld crown geometry, as well as the six (6) previously referenced planar flaws from the upper side of the weld.
The 60'RL also recorded norwelavant indications and insiaa surface weld crown geomeby from both sides of the weld. along withwelding discontmuities from the lower side. as weil as shear component and four (4) of the previously referenced planar flaws tnxn the upper aide of the weld.
The OD creeping wave search unit recorded nan<<alevant indicauans trom bath sides of the weld. along with welding discontmuities fram the lower side of the wakt.
This examinationwaslimited to L dimensionsof12'to157'and 267 to344'tromvessel'0'duetotheproximityoflitttngandvibrationtugs, top guide pins, and care spray downcameis.
Circumferential L"dimensions for all axaminatxNI scans were recorded in angular units in lieu ot SUM BY IO.Z.I.'l4 LEVEL DATE
/4 pter DATE GER B
LEVEL DATE AHIIREVIEW PAG~OF:~
T~~MV~
II
GE Nuclear Energy EXAMINATlONSUINMARYSHEET REPORT NO.
MB&Q6 PROJECT:
PROCEDURE'EV~
FRR:~
SYSTEM:
WELD NO.:
CONFIGURATION'EV~
FRR~
FRRL~
EXAMINER:
EXAMINER:
EXAMINER:
DATASHEET NO (S):
LEVEL:
ll LEVEL:
LEVEL:
ILIE ClMT QPT OUT QVT Q CIRCUMFERENTlAL Q LONGlTUDINAL 8 OTHER~EOllD CAL SHEET NO.(S):
1 During the examination of the above referenced weld; no surface connected planar flaws or any indications associated with IGscc IlAscc wer recorded by me Smart 2000 system utilizing45 shear wave. 60'efracted longitudinal wave, and OD creeping wave search units The 45'hear. 60'L. and OD creeping wave searcn unns did record no~levant indications from the lower side of the weld.
No examinabon was pefoimed from the upper side of the weld due to component configuration. This examinabon waa also limited dimensions of approximately 10'o 16'nd 188'o 184 from Vessel "0 due to the proximity of liftingand vibration lugs, top guide pins, Corespray downcomers. Jet pumps and their associated braces and restraint brackets.
Circumferernial l: dimensions for att examirtabon were record ed in angular unns m lieu of linear units. The conversion factor for circumferential measurements is 1.75 per degree.
SUlklARYB GE REtntaiVED BY io zs.w i
LEVEL DATE LEVEL ATE UTlUTYREVlEtN 4/a ANllREVIEVV
/d Z5 DATE DATE PAGE~OF:~
KWW%W,~
Il
~I J
GE-Nuclear Energy EXAMINATlON
SUMMARY
SHEET REPORT XO.
ME9%QZ PROJECT:
1 NW PROCEDURE'EV~ FEL~
SYSTEM:
WELD NO.:
REV~ FRR:~
CONFIGURATION'XAMINER:
EXAMINER'XAMINER:
L'EVEL:
LEVEL:
il LEVEL:~vr
'WELD TYPE:
REV~ REL~
aMT OPT atIT OVT Q CIRCUMFERENTIAL E3 LONGITUDINAL 0 OTHER~QQ DATASHEET NO:(S):
CAL SHEET NO.(S):
During tne examination of the above referenCed weld. no surface connected planar fhws or any indications associated with IGSCC I IASCC wei recorded by the Smart 2000 system utilizing45'hear wave. 60'efracted longitudinal wave, and OD creeping wave search units.
The 45 shear. 60 RL. and OD creeping wave searcn unns did record no~levant indications from the lower aide of the weld.
No examination was pefonned from the upper sxle of the weld due to component configuration.
The examination from the lower aide ofthe wet was limited due to the proximity of the outside diameter bacxing nng and weld buiid4ip area.
This exanunat}on was also limitedto L>> dime of a pproximately 10'o 16'nd 188'o 190'rom Vessel "0" due to the proximityof liftingand vibration lugs, top guide pins, Corespray downcomers. Jet pumps and their associated braces ano restraint brackets.
Circumferential L dimensions for alt examaation scans were recorded in angular units in lieu of linear units. The conversion factor for circumferential measurements is 1.75" per degree.
8UMIVRYBY GE REVIEWED BY ID E'E 94 I
LEVEL DATE
/@~~M UTIUTYREVIEW AI A ANa REVlEW Ic ~g 55 DATE DATE PAG~OFt~
C IV SAFETY ANALYSIS
SUMMARY
TVA and GE performed an analysis of the core shroud cracks identified in Unit 2 to show that restart and resumption of operation for at least two cycles would be acceptable.
The analysis was based on the fracture mechanics limit load based screening criteria and evaluation techniques applicable to BFN.
The analysis reports used for these assessments are available on-site for review.
The screening criteria establishes the allowable flaw lengths for the various girth and axial welds on the core shroud.
The evaluation techniques provide guidance for evaluating inspection results.
'The screening criteria and evaluation techniques are conservative and bound the BFN inspection results since they are based on the presumption that only visual inspections will be conducted.
As such, allowable flaw lengths were established assuming that. all flaws would be through-wall.
Flaw indications were observed in only three of the seven
.Unit 2 horizontal shroud welds inspected.
The indications
.in welds H3 and H5 are largest with essentially equal lengths of 9.41 inches and 9.09 inches, respectively, while the indication in weld H2 is only 1.34 inches long.
None of the indications were significant enough to warrant evaluation.
The H5 weld is in a low fluence area (i.e.,
below 3.0 x 10 n/cm ) so Linear Elastic Fracture Mechanics (LEFM) evaluation techniques are not needed.
TVA examined approximately 61.724 of the H5 weld.
In the weld length examined, 2.34 was found to be cracked.
TVA considers that any cracks in the unexamined portions of the weld would be similar to those found (e.g.,
2.34 of the unexamined weld was assumed to be. cracked).
The deepest crack had a depth of 0.96 inches and a length of 1.63 inches.
The longest continuous crack was 2.9 inches with a maximum depth of 0.74 inches.
An evaluation of the H5 weld was performed to estimate the extent that the cracking may propagate during the next two cycles of operation.
ASME Section IX proximity rule (2*flaw depth
+ 2*flaw growth) was used in evaluating the data since flaw characteristics were determined by UT.
To account for the uncertainty in depth sizing by UT, TVA added 0.3 inches to the flaw depths.
The flaw growth rate was estimated using conservative values that have been accepted by NRC (5.0 x 10~ inches/hour of hot operation).
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A calculation was performed using the evaluation method to determine if the postulated flaw sizes would meet the acceptance criteria through two operational cycle (assumed to.be 12,500 hot operating hours per fuel cycle).
The results of the evaluation are shown below:
UNIT DESCRIPTION
.Total On-Line Hours at End of Cycle Total Effective Flaw Length, inches
'Allowable Effective Flaw Length, inches 4 Margin Maximum 90 Window Indications Length,
'inches (for information only)
Allowable 90 Window Indications Length, in CYCLE 9 107,700 38 416 86 17 104 V
CONCLUSIONS Based on the analysis summarized
- above, TVA considers that it is acceptable to operate Unit 2 through the Cycle 9
operating cycle.
The results of the inspection confirm that cracking in the Unit 2 core shroud welds is limited and does not pose significant near term concern for structural integrity.
This conclusion is based on a significant indicated margin (approximately 90 percent margin of safety after one operating) which in turn is conservatively established.
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