ML18038B823
| ML18038B823 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/09/1997 |
| From: | Abney T TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-80-103, NUDOCS 9703170070 | |
| Download: ML18038B823 (26) | |
Text
CATEGORY j.
5'EGULATIQ INFORMATION DISTRIBUTIONSTEM (RIDE)
ACCESSION NBR:9703170070 DOC.DATE: 97/03/09 NOTARIZED: NO DOCKET FACIL:50-296 Browns Ferry Nuclear Power Station,-Unit 3, Tennessee 05000296 AUTH.NAME AUTHOR AFFILIATION'BNEYFT.ED Tennessee Valley, Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Forwards supplemental info for evaluation of indications at core spray sys piping collar to shroud weld. Encl 2 contains photograph of core spray downcomer a collar.
DISTRIBUTION CODE:
IE10D COPIES RECEIVED:LTR ENCL
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TITLE: 50 Dkt Augmented Inspection Team (AIT) Reports/Correspondence NOTES:
RECIPIENT ID CODE/NAME PD2-3-PD INTERNAL: 'ACRS AEOD/SPD/RAB DEDRO NRR/DISP/PIPB NRR/DRPM NRR/DRPM/PERB
'NRR/DSSA/DIR OE/DIR OGC/HDS3 EXTERNAL: INPO, RECORD CTR NRC PDR COPIES LTTR ENCL 1
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1 RECIPIENT ID CODE/NAME WILLIAMS',J.
AEOD/DO COMM IONERS CE NRR DRCH/HHFB NRR/DRPM/PECB NRR/DRPW NUDOCS-ABSTRACT OEDO RGN2 FILE 01 NOAC NUDOCS'ULLTEXT COPIES LTTR ENCL 1
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1 NOTE 'TO ALL "RIDSN RECIPIENTS:
PLEASE HELP US TO REDUCE 'WASTE!
CONTACT THE DOCUMENT CONTROL DESK, ROOM OWFN 5D-5(EXT. 415-2083)'O ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!
TOTAL NUMBER OF COPIES'EQUIRED:
'LTTR 28 ENCL 28
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Tennessee Valley Authority, Post Office Box 2000; Decatur, Afabarna 35609-2000 March 9, 1997 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C..
20555 Gentlemen:
In the Matter of Tennessee Valley Authority Docket No. 50-296 BROWNS FERRY NUCLEAR PLANT (BFN),'
UNIT 3 REACTOR PRESSURE VESSEL INTERNALS, AUGMENTED WELD INSPECTION SUPPLEMENTAL INFORMATION FOR EVALUATION OF'NDICATIONS AT THE'ORE SPRAY SYSTEM PIPING COLLAR-TO-SHROUD WELD On March 7, 1997, in accordance with IE Bulletin 80-13, "Cracking in Core Spray Spargers,"
TVA submitted a structural evaluation of weld indications identified during ultrasonic (UT) examinations of the Core Spray (CS) piping collar-to-shroud welds.
On March 8,
- 1997, the staff requested'dditional information concerning the evaluation.
Enclosure 1 to this letter contains the additional information requested by the staff.
Enclosure 2 contains a photograph of the core spray downcomer and collar.
9703170070
'F70309 PDR ADOCK 050002'V6 G.
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U.S. Nuclear Regulatory Commission Page 2
NR, vg )gg There are no commitments described in this letter. If you have any questions regarding this information please call me at,(205) 729-2636.
cerely T. E. Abner Manager of icensi g
and Indu try Aff irs Enclosure CC':
(Enclosure)
Mr. Mark S. Lesser, Branch Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant 10833,Shaw Road
- Athens, Alabama 35611 Mr. J.
F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852
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ENCLOSURE 1
TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 3 CORE SPRAY SYSTEMS AUGMENTED WELD'NSPECTION SUPPLEMENTAL INFORMATION FOREVALUATION OF INDICATIONS AT THE 'COLLAR-TO-SHROUD WELD (SEE ATTACHED)
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Regarding the indications seen on the core spray C downcomer, P4D elbow weld:
Provide. an explanation why these indications are most likelythe product ofcold work as opposed to IGSCC initiated from the pipe inside diameter.
Response
The indications at the P4D weld are minor and are mostly axial (very small'circumferential component).
These axial indications were likely'initiated on the outside ofthe piping for the followingreasons:
A. The P4D weld is a groove weld and contains no crevice.
Cracking at other plants at groove weld, locations show that outside diameter (OD) cracking can:be initiated on the piping.
This is supported by the excellent agreement between Ultrasonic Testing (UT) and visual examination results.
B. The BFN Unit 3 elbow was ground on the OD during the sparger rework process performed during construction.
Data obtained from the core shroud cracking experience showed that cold work due to grinding can accelerate initiation ofIGSCC.
A review of core spray cracking lengths identified at other. plants is provided in Table 1.
Cracking has been detected at this location (P4D) in several plants, included is data referencing Plant E. In Plant:E's case it was possible to apply UT to confirm the crack length, after visual detection.
It was determined that the crack'lengths obtained by UT matched the lengths obtained by, the visual examination.
In fact, for similar welds at other plants, except for the severe crevice locations such as the downcomer slip joint, the cracks that were sized by visual examination compared well with the sizing performed by UT methods.
An example ofthis is shown in Table 1 for the'Plant B pipe to elbow weld.
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The only instance where cracking was found visually on the OD ofthe core spray piping, which had a fairly large inside diameter (ID) component determined by UT was at the downcomer slip joint location. This is a.severe crevice weld; For.the:plant that discovered these findings accurate sizing was,not attempted during the visual exam. It is believed that with a. more careful visual examination,, the crack length determined visually would have been in better agreement with the UT results. It is important to note that at BFN Unit 3 all ofthese downcomer, slip joint welds were examined by UT and were found to be free ofindications.
Table 2 provides information on core spray cracking incidences by location.
The field. data indicates that the environment is not likely to be more aggressive on. the outside ofthe core spray, piping versus the inside ofthe core spray piping. However, there are other factors such as grinding on the outside of the piping and'the presence of severe crevices that-can affect the core spray piping susceptibility to cracking.
The core shroud cracking experience has shown that cold work due to grinding can accelerate initiationofIGSCC. To date the most significant shroud cracking (extent and depth) has occurred at locations where grinding has been, performed.
Specifically, the shroud rings that were fabricated from plates, welded, and then ground typically show more cracking than the shroud shell welds.
During the Unit 3 core spray sparger re-work, grinding did take place on the elbow at the weld P4D location.
As discussed above,,this grinding could act as an initiator for IGSCC on the OD ofthe piping.
The dated weld records indicate the;P4D weld was made as a closure weld for the piping subassembly.
The weld records also indicate that the P9 weld was made several'days earlier, and itwas made on a new transition piece spool, receiving a satisfactory PT on the ID'and OD upon completion. While P9 was not made as a, shop weld, these modifications were made with the shroud temporarily stored in the Unit 3 Equipment Pool, affording construction personnel improved access to the work.
Based on industry field.data and the fabrication history ofBFN Unit 3 core spray spargers and piping, it is reasonable to conclude the indications found on the OD ofweld P4D
initiated on.the outside diameter ofthe piping. Therefore there is high confidence that the crack lengths determined from the visual examination:are representative ofthe true crack lengths.
These crack lengths were also treated very conservatively in the structural margin analysis. Although these cracks were mainly axial, the analysis as described in'the March 7, 1997 submittal, conservatively assumed the cracks to be circumferentially oriented'and assumed that the two cracks were one crack. The evaluation showed that there is significant margin to the allowable flaw size.
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Table 1: Review ofCore Spray Cracking Lengths for Non-Crevice and Potentially Crevice Welds Plant indication Crack Crack length by length by visual (in)
UT (in)
Degrees of cracking based on UT Crevice Crevice Crevice Length Gap.
Geometry 260 degree elbow to transition piece weld 4.6 4.6 80 No 290 degree elbow to transition piece weld 3,4 3,4 121 No B
B 260 degree Pipe to elbow weld Loop A 290 degree collar
. weld 3.5 3.5 61 29
>1.0"
-0.5" No Loop B 260 degree collar weld 2.25, 0 5.5, 3 121
>1.0"
-0.5" Loop A collar weld 1 Loop A collar weld 21 10 5.5 8.9 5.5 160 99
>1.0"
>1.0"
-0.5"
-0.5" Loop B upper piping near T-box 1.5 No
- Potential crevice based on geometry, but field data does not show this to be a true severe crevice El-5
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Table 2: Core Spray Cracking:Incidences by Location Location Number ofCracking Incidences Piping at T-box T-box cover Plate Horizontal Piping Upper Elbow Vertical Piping Slip joint Lower Elbow Collar (Collar location in shroud) 5 2 (4)
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2.
Regarding the core spray T-Box indications (previously identified'during IVVIprior to Unit 3 Restart), which have had the welded. brackets installed as a fullstructural repair, identifyifthe indications have exhibited growth;
Response
The indications located on the 120'nd 240'-Boxes exhibited no discernible growth from that previously reported.
Regarding the core spray C downcomer, P4D indication, are UT examinations available of this indication?
Response: No. Due to radius ofthe elbow,,acoustic contact can not be maintained with
,available ultrasonic equipment. Additionally,,the pipe side ofthe elbow does not'provide suf5cient area to perform an ultrasonic examination Regarding the core:spray, P8A locations, how much ofthis weld was examined'by UT?
Response
The ultrasonic examination performed on weld P8A was a "best effort" and was limited to approximately 25% ofthe area ofinterest. The scanning was.performed only from the collar side ofthe weld with the ultrasonic beam oriented perpendicular to the weld; An ultrasonic examination from the piping surface is not possible due to component geometry. The examination performed was'not successfully demonstrated on the BWRVIP mockup at the EPRI NDE center, due to the location ofthe flaw'implants (inner surface); Flaws that. could be detected using;this ultrasonic technique would be limited to.flaws originating. at the collar side ofthe weld and withinthe outer 25%.of the base material. An enhanced visual examination was additionally performed. on these locations.
Regarding the core spray C downcomer, P8B indications. Provide an. explanation why it is. believed that these indications are most likelyin:the Shroud metal, rather than the collar material.
Response
To,perform the ultrasonic examination ofthe P8B weld, the GE CSI-2000 remote operated vehicle (ROV) was latched onto the piping system above the slip joint assembly. The. scanning head was then rotated into position and lowered into the annulus area and placed onto the collar assembly. The contoured'search.unit package was then manipulated on the collar side ofP8B weld until acoustic contact was achieved, then the search unit package was locked'into position. The scanning head.was then electronically "zeroed" for positioning information with the search units on.the top side. ofthe collar and at the toe ofthe weld on the collar side. The search unit setup is entirely reliant on the operator's discretion-
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ofwhen the search unit is coming in contact with the weld surface. Since the. scanning head masks the view ofthe search units, the setup is best e6ort. Scanning is then conducted with the ultrasonic beams oriented perpendicular to the weld axis.
To accurately plot ultrasonic information the exact location ofthe search unit acoustic exit point must be known. With thin wall material such as the BFN-3 collar (approx. 0.160")
the exact location ofthe search unit is even more critical; Therefore, conventional ultrasonic plotting offlaw location could not be performed. The inabilityto perform meaningful ultrasonic'plotting is attributable to the dif5culty in determining exact search unit location, ultrasonic. beam spread'in thin material, and the reliance on multi-nodal'ignal responses for flaw detection.
However by. viewing the ultrasonic A-Scan presentation-while scanning on the collar, the approximate location-of the toe ofthe weld could be ascertained.
Using,the weld-toe Y-axis information and the ultrasonic metal path reading, it can be determined with a high level ofconfidence that the indication is originating Rom the shroud side ofthe weld.
Referencing GE-NE-B13-01869-032, Rev 1: Please be advised that paragraph four of 1.
INTRODUCTIONANDBACKGROUND, second sentence; incorrectly refers to a filet weld.
Response
This sentence should read as follows:
"Two indications were noted that originate &om the toe ofthe groove weld'at an angle of 30's measured from the axis ofthe pipe."
Referencing the initialIVVI,photograph GE provided for core spray C downcomer for P8A/P4D; the indications-were annotated-as. being each 1/2" in length, and 3/8" apart.
Subsequent photos provide more detailed. dimensions.
Response
During the enhanced visual examination ofthe P4D weld on core spray downcomer C, two linear indications were noted and initiallyreported to be approximately 1/2" long and separated:at the weld toe by approximately 3/8". Subsequent analysis using video enhancement systems revealed that the indications were actually 1/4" and 1'/2"'in length respectively.
Additionallyitwas determined that the'indications were separated by 1/8" at their closest point as determined by digital measurement.
The separation distance at the toe ofthe weld is approximately 3/8", as initiallyreported.
The measurements achieved using the video enhancement system should be more precise in estimating the actual flaw dimensions.
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ENCLOSURE,2 TENNESSEE VALLEY, AUTHORITY BROWNS FERRY NUCLEAR PLANT,(BFN)
UNIT 3 CORE 'SPRAY SYSTEM~
AUGMENTED WELD INSPECTION ~
.EVALUATION OF INDICATIONS AT THE COLLAR-TO-.SHROUD WELD
'J CORE'PRAY DOWNCOMER AND COLLAR'HOTOGRAPH
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Core Spray C Doivncomer
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