ML20077L681
| ML20077L681 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/14/1983 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-SSINS-6820 830718, IEB-83-02, IEB-83-2, NUDOCS 8308090515 | |
| Download: ML20077L681 (11) | |
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y TENNESSEE VALLEY AUTHORITY
.UbOPC p CH ATTANOOGA, TENNESSEE 37401 400 Chestnut Street Tower II
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July 18, 1983 U.S. Nuclear Regulatory Commission Region II ATTN: James P. O'Reilly, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303
Dear Mr. O'Reilly:
INSPECTION AND ENFORCEMENT EULLETIN 83 STRESS CORROSION CRACKING IN LARGE DIAMETER STAINLESS STEEL RECIRCULATION SYSTEM PIPING AT BWR PLANTS - BROWNS FERRY NUCLEAR PLANT -
Enclosed is our response to the subject bulletin for the Browns Ferry Nuclear Plant unit 1.
Our response contains the results of the inspections performed on the recirculation and Residual Heat Removal Sytems and the planned weld repair program.
A meeting was held between TVA and the NRC staff in their Bethesda offices on July 6, 1983 That meeting was attended by F. Cantrell, J. Blake, G. Paulk, and others of your staff. The enclosed response includes additional information requested by the NRC staff in that meeting. The requested information regarding weld crown widths will be forwarded when it becomes available.
The enclosed response states our positions regarding the criteria for determining the need for repair and the overlay repair procedure. We need to obtain the NRC staff's final position on the criteria and overlay repair immediately since neeCad unit 1 repairs are already underway.
If you have any questions, please call Jim Domer at FTS 858-2725.
To the best of my knowledge, I declare the statements contained herein are complete and true.
Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, anager Nuclear Licensing i
Enclosure cc: See page 2 s\\
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-Mr. James P. O'Reilly July 18, 1983 cc (Enclosure):
U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.
20555 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Mr. R. J. Clark Browns Ferry Project Manager
. U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 l'
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ENCLOSURE The welds examined in the Recirculation and RHR Systems and the results of the examihations were reported in the meeting on July 6,1983 between TVA and the NRC staff.
The following is a summary of what was presented at the meeting.
TVA examined the following~ welds.
Recire (100% of welds)
RHR (100% of stainless steel piping welds)
Risers -
40 Sweepolets -
8 Supply (20") -
7 Large Diameter -
41 Return (24") -
25 91 32 Of these, the following crack distribution was reported:
Recire RHR 6
Supply &
Risers 14 4
Return Sweepolets Large Diameter -
2jl 33 Of these 47 cracked welds, TVA proposed to overlay repair 30 and proposed to accept "as is" the other 17 because of the acceptability demonstrated by the flawed pipe analysis.
As a result of increased cracking detected by all utilities performing IEB 83-02 inspections, NRC expressed concern in the July 6 meeting over continued operation without overlay repair of any large diameter recirculation of RHR piping with cracking of 25-percent throughwall or greater. This concern affects the following unit 1 recirculation system welds which TVA has determined by conservative sizing techniques and flawed pipe analysis to be acceptable for continued operation for one fuel cycle without repair:
KR-1-24, KR-1-48, GR-1-56, GR-1-64, KR-1-47, GR-1-27, GR-1-57, KR-1-45, GR-1-61, and KR-1-52.
In addition, NRC stated that they are considering requiring utilities to perform " full structural" overlay repairs instead of the standard size overlay repairs currently being performed by the industry. The following comments address these two NRC concerns.
1.
TVA disagrees with an arbitrary cut-off point of 25-percent throughwall indications as a criteria for determining repairs for large diameter piping because it does not take into account the applied stress at a given weld and ignores the conservatism used by TVA in sizing all indications. The ten recirculation welds identified by NRC in the July 6 meeting (identified above) have relatively low-applied stresses as compared with typical RHR welds and hence the crack growth rate is much less.
In addition, the ten welds in question can have a considerable margin of error in sizing and still operate safely for one 18-month cycle of
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operation. The data for these ten welds are summarized below. The description of the indications for these ten welds is presented on page 1 of Attachment 2.
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Allowed Initial Initial Crack Crack Size for Percent Error Size (Percent One Cycle Margin for Safe Weld No.
Throughwall)
(Percent Throughwall)
Operation KR-1-24 25 51 104 KR-1-48 30 50 67 GR-1-56 29 50 72 GR-1-64 33 51 55 KR-1-47 23 50 117 GR-1-27 37 52 41 GR-1-57 33 51 55 KR-1-45 23 -
41 78 GR-1-61 30
- 51 70 KR-1-52 27 50 85 As presented in the July 6 meeting, TVA used very conservative residual stress and IGSCC crack-growth curves in performing the flawed pipe analysis and in every case assumed the maximum recorded flaw depth to be 3600 around the weld. As pointed out in the July 6 meeting, TVA has a very high confidence level in our. examination technique for the following reasons:
(1) a transfer technique was employed before scanning every weld to account for acoustic differences and to ensure uniform sensitivity; (2) all scanning was performed using the half-node technique to reduce metal' path and hence the propensity for error; (3) all sizing was performed using a 600 transducer and the half-node technique; and (4) a sizing technique was used which the NRC Region II inspector indicated was very conservative.
Based on the above data and the conservatisms used in the examinations and flawed pipe analysis, it is TVA's position that the ten recirculation piping welds identified above have more than an adequate margin of safety to operate for one fuel cycle without an overlay repair.
2.- 'TVA has serious problems with the " full structural" overlay concept for the following reasons. A " full structural" overlay is more th;m twice as thick as the standard overlays currently being performed by most utilities. The compressive residual stresses developed by the standard overlay-put a compressive stress around the crack tip. Flawed pipe analyses demonstrate zero crack growth for at least 5 years.
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_3-1 Therefore, thicker overlays are not warranted from a structural integrity viewpoint. The increased thickness of " full structural" overlays significantly reduce the inspectability of the repair joint.
TVA, as well as the rest of the industry, is committed to producing the most inspectable overlays possible, and " full structural" overlays defeat this purpose. Of greater concern to TVA, however, is the adverse effect that " full structural" overlays may have on the rest of the piping system. Due to the amount of shrinkage involved with overlays of this thickness, the resultant stress at adjacent welds and welds at or near terminal ends is expected to increase significantly.
Given the present number of overlays currently planned for unit 1, it is.TVA's opinion that " full structural" overlays could adversely affect the structural integrity of the recirculation and RHR systems.
We also believe it is important to consider the tremendous time increase associated with performing " full structural" overlays. Below is a comparison of the time required to perform standard overlays versus " full structural" overlays for three pipe diameters (provided by TVA's prime welding contractor for unit 1):
Pipe Diameter Standard Overlay Full Structural Overlay (Inches)
(Hours)
(Hours)
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12.75 6.7 93 22.00 19.3 45.0 28.00 28.6 72.5 As can be seen from the above comparison, for large diameter pipe it takes approximately 2-1/2 times longer to perform a " full structural" overlay than to perform a standard overlay. Given the number of welds currently planned to be repaired on unit 1, TVA's welding contractor.
estimates it would take an additional 40 days to perform " full structural" overlays. In addition, the man-rem exposure will significantly increase.
In summah LTVA believes that the ten large' diameter welds in question have more than an adequate margin of safety to operate for one fuel cycle without an overlay repair. In addition, TVA plans to utilize the overlay designs recommended by NUTECH Engineers, Inc., the prime contractor for,the overlay repairs on unit 1.
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J REruits of Cr:ck Growth Antlycic Lg'.
(Large Diameter Recirculation Piping) l^
4 1 Allowed Initial I
Crack' Depth Crack Size for
. Initial Crack at 18 Mos.
18 Mos. Cycle Months to Months to Size (Percent (Percent (Percent 50-Percent 63-Percent Weld No.
Throughwall)#
Throughwall)
'Throughwall)
Throughwall Throughwall-Disposition KR-1-37 35 42 55 37 68 overlay KR-1-34 8
23 46 55 69 Accept as is
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KR-1-15 27 35 54 54 84 overlay 4"
KR-1-12 6
25 30 35 40 Accept as is 10 23 overlay.
KR-1-3 43 i
KR-1-24 25 36 51 46 68 Accept as is 2
GR-1-1.
8 22 50 63 81 Accept as is GR-1-2 15 29 50 52 70 Accept as is GR-1-3 35 46 48 23 39 overlay KR-1-2 15 30 47' 48 63 Accept as is-I GR-1-58 45 8
26 overlay
.k KR-1-48 30 41 50 34 52 Accept as is GR-1-56 29 40 50 36 55 Accept as is GR-1-64 33 42 51 33 54 Accept as is 1
KR-1-47 23 35 50 43 61 Accept as is GR-1-27 37 46 52 26 48 Accept as is GR-1-57 33 43 51 30 50 Accept as is KR-1-45 23 38 41 32
'43 Accept as is l
2 16 Overlay
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GR-1-54 49 KR-1-25 14 28 51 59 80 Accept as is i
i GR-1-60 36 46 50 24 43 Overlay GR-1-61 30 40 51 37 59 Accept as is ti KR-1-52 27 37 50 40 60 Accept as is j
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'Where these vary from the approximate percent in attachment 2, the percent is always greater and theratore the calculations are more conservative.
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ATTACHMENT 2 KR-1-24 28" Pipe / Elbow Elbow Side of Weld 8 2:30 approx. 2" long Approx. 10% thru wall e 4:30 approx. 2" long Approx. 17% thru wall 9 11:00 approx. 3" long Approx. 25% thru wall 8 12:35 approx. 4" long Approx. 8% thru wall Pipe Side of Weld 9 4:30 approx. 3" long Approx. 95 thru wall KR-1-45 28" Pipe / Elbow Indications 3600 intermittent both sides of the weld Approx. 23% thru wall 4
KR-1 47 28" Pipe / Elbow Elbow Side of Weld
@ 5:00 to 8:00 approx. 21" long Approx. 23% thru wall Pipe Side of Weld 8 5:00 to 8:00 approx. 21" long Approx. 20% thru wall KR-1-48 28" Pipe / Elbow Indications 3600 intermittent both sides of the weld Approx. 28% thru wall KR-1-52 28" Pipe / Elbow Elbow Side of Weld Indications 3600 intermittent Approx. 27% thru wall OR-1-27 28" Pipe / Pump Discharge Side Pipe Side of Weld 8 6:30 approx. 1" long Approx. 36% thru wall max.
't 8:30 approx. 1" long 810:00 to 11:00 approx. 7" long 9 12:00 to 2:00 approx. 14" long 9 4:45 approx. 1" long OR-1-56 28" Pipe / Valve Elbow Side of Weld 8 12:30 to 3:00 approx. 17-1/2" long Approx. 295 thru wall OR-1-57 28" Pipe / Valve Pipe Side of Weld Indications 3600 intermittent Approx. 32% thru wall GR-1-61 28" Pipe / Pipe
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Upstream Side of Weld e 5:30 approx. 5" long Approx. 28% thru wall
@ 8:00 approx. 12" long
_ Approx. 23% thru wall Downstream Side of Weld 9 7:30 to 11:00 approx. 25" long Approx. 30% thru wall 4h w
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KR-1-12 228 Pipe / Cross Pipe Side of Weld 87:00 approx. 3" long Approx. 6% thru wall KR-1-34 22" Pipe /Crhss Pipe Side of Weld e 6:00 approx. 4" long Approx. 8% thru wall 83:00 approx. 6" long Approx. 6% thru wall KR-1-37 22" End Cap Cap Side of Weld 8 11:30 to 3:00 approx. 19" long Approx. 35% thru wall 8 7:00 to 8:30 approx. 9" long Approx. 35% thru wall KR-1-14.
.Sweepolet-Weld Saddle Side'of Weld 8 5:30 approx. 2" long Approx. 10% thru wall e 6:20 approx. 2" long Approx. 10% thru wall Header Side of Weld
-8 11:20 approx. 9" long Approx. 19% thru wall KR-1-20 Sweepolet Weld Header Side of Weld e 2:00 approx. 1" long Approx. 29% thru wall KR-1-36 Sweepolet Weld Saddle Side of Weld
@ 12:00 to 3:00 approx. 18" long Approx. 25% thru wall e 8:00 to 9:00 approx. 6" long Approx. 25% thru wall KR-1-42 Sweepolet Weld Header Side of Weld-
- 4:00 approx. 1" long Approx. 38% thru wall 8 10:00 approx. 1" long Approx. 20% thru wall KR-1-16 12" Pipe / Elbow Pipe Side of Weld Indications 3600 intenaittent Approx. 35% thru wall KR-1-18 12" Pipe / Elbow Pipe Side of Weld j
Indications 3600 intermittent Approx. 35% thru wall KR-1-21
-12" Pipe / Elbow Pipe Side of Weld Indications 3600 intermittent Approx. 35% thru wall
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KR-1-22 12" Pipe / Elbow l
Pipe Side of Weld Indications 3600 intermittent Approx. 35% thru wall GR-1-41 12" Pipe / Tee l
Pipe Side of Weld l
@ 11:00 to 1:00 approx. 6" long Approx. 125 thru wall L
f 9:00 appro'x. 3"-long Approx. 8% thru wall n
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4 GR-t-64 28" Elbow / Pump Intake Side Elbow Side of Weld Indications 3600 intermittent Approx. 33% thru wall GR-1-54 28" Pipe / Elbow Indications 3600 intermittent both sides of the weld Approx. 45% thru wall GR-1-58 28" Elbow / Pump Intake Side Pipe Side of Weld Indications 3600 intermittent Approx. 45% thru wall GR-1-1 28" Pipe / Pump Discharge Side Pipe Side of Weld 8 2:00 to 5:00 approx. 21" long Approx. 6% thru wall e 6:30 to 8:00 approx.10-1/2" long Approx. 8% thru wall i 10:00 approx. 1" long Approx. 10% thru wall GR-1-2 28" Pipe / Valve Pipe Side of Weld Indication 3600 intermittent Approx. 15% thru wall GR-1-3 28" Pipe / Valve Pipe Side of Weld Indications 3600 intermittent Approx. 33% thru wall KR-1-2 28" Pipe / Elbow Pipe Side of Weld Approx. 6% thru wall 8 11:30 to 12:30 approx. 7" long
- 2:00 to 8:00 approx. 42" long Approx. 15% thru wall Elbow Side of Weld 8 2:30 to 3:30 approx. 7" long Approx. 8% thru wall KR-1-3 28" Pipe / Tee
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Pipe Side of Weld Indication 3600 intermittent Approx. 43% thru wall GR-1-60 28" Pipe / Elbow Pipe Side of Weld 6 4:00 approx. 3" long Approx. 29% thru wall Elbow Side of Weld-6 11:30 to 1:30 approx. 14" long Approx. 18% thru wall 8 10:00 approx. 3" long Approx. 36% thru wall KR-1-25 28 Pipe / Tee Pipe Side of Weld 8 8:00 to 3:00 approx. 49" long Approx. 14% thru wall KR-1-15 22" End Cap
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- Pipe Side of Weld 95:00 to 7:00 approx. 12" long Approx. 14% thru wall Cap Side of Weld Indications 3600 intermittent Approx. 27% thru wall
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o GR,1-46 12" Pipe / Elbow Pipe-Side of Weld Indications.3600 intermittent Approx. 20% thru wall
.DSRHR 1-4 24"-Pipe / Elbow Elbow Side of Weld 8 11:00 to 2:00 approx. 18" long Approx. 30% thru wall e 8:30 approx. 1" long Less than 10% thru wall DSRHR 1-4A 24" Elbow / Elbow Upstream Side of' Weld Indication 3600 intermittent Approx. 44% thru wall DRHR-1-4 24" Pipe / Elbow Pipe Side of Weld e 7:00 approx. 1" long Less than 10% thru wall e 9:00 approx. 1" long Less than 10% thru-wall 0 10:30 approx. 1" long Less than 10% thru wall DSRHR-1-5 24" Pipe / Elbow Elbow Side of Weld 9 2:00 approx. 7" long 31%.thru wall 6 8:00 to 12:00 approx. 25" long 31% thru wall DSRHR-1-8B 24" Pipe / Elbow Pipe Side of Weld 8 12:00 to 3:00 approx. 20" long Approx. 41% thru wall Elbow Side of Weld 8-1:00 to 3:00 approx. 14" long
- Approx. 31% thru wall DRHR-1-8 24" Pipe / Valve Pipe Side of Weld
@ 11:00 approx. 5" long Approx. 25% thru wall DSRHR-1-9. 20" Pipe / Elbow Elbow Side of Weld i
i 7:00 to 11:00 approx. 28" long Approx. 29% thru wall
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Pipe Side of Weld 8 12:00 approx. 3" long Approx. 30% thru wall 9 10:30 approx. 3" long Approx.12% thru wall Elbow Side of Weld 8 12:00 approx. 6" long Approx. 23% thru wall i
DSRHR-1-11 20" Pipe / Elbow Elbow Side of Weld 0 6:00 to 9:00 approx. 19" long Approx. 24% thru wall DRHR-1-15 24" Pipe / Valve Pipe Side of Weld e 6:00 approx. 8" long Approx. 30% thru wall DRHR-1-17 24" Pipe / Valve Pipe Side of Weld Indications 3600 intermittent Approx. 31% thru wall y,
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. 24" Pipe / Tee Pipe Side of Weld 8 12:00 to 3:00 approx. 20" long Approx. 165 thru wall 8 7:00 approx. 4" long Approx. 20% thru wall DRHR-1-20 20" Elbow / Valve Elbow Side of Weld Indications 3600 intermittenti Approx. 43% thru wall DRHR-1-5 24" Elbow / Valve Elbow Side of Weld Indication 3600 intermittent Approx. 36% thru wall Y
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