ML20006E261
| ML20006E261 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 02/09/1990 |
| From: | Schuster T COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| IEB-88-009, IEB-88-9, TAC-M72648, NUDOCS 9002220465 | |
| Download: ML20006E261 (3) | |
Text
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'N Commonwealth Edison
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/ 1400 Opus Place
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'O J Downers Crove, Illinois 60515 a
s Februari 9, 1990 1
Dr. Thomas E. Murley, Director
_ Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
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Subject:
Byron Station Units 1 and 2 Response to NRC Bulletin 88-09 NROJocket Nots _10-hs4/455 Referencet (a) NRC Bulletin No. 88-09, dated July 26, 1988 (b) September 13, 1988 letter from L. N. 01shan to H. E. Bliss approving the alternate thimble tube thinning inspection schedule for Byron Unit 1.
(c) March 17, 1989 letter from M. H. Richter to USNRC regarding thimble tube thinning inspections for Byron Unit 2 l
(d) TAC # M72648 4
Dear Dr. Murley,
Reference (a) requested that addressees establish and implement an inspection program to periodically confirm incore neutron monitoring system thimble tube integrity at Westinghouse designed nuclear power reactors.
In.
J accordance with Bulletin 88-09, this letter presents the details of the incore thimble tube inspection program (Action 1) and the results of the thimble tube inspections (Action 2.a) performed during the third refueling outage for Byron Unit 1.
The letter of reference (b) authorized the Byron Unit 1 inspections to take place during this outage. The letter of reference (c) provided J
results of the initial Unit 2 inspections completed by March 1, 1989, and is included as Attachment B.
The thimble tube inspections are performed using eddy current testing
. methodology. The inspections will be performed at every refueling outage until sufficient data has been accumulated to generate a baseline and correlation for thimbic tube thinning. At that time, the inspection frequency will be evaluated and may be adjusted as appilcable.
It is expected that at h
least two inspections will be necessary to accumulate sufficient data before consideration of any change in inspection frequency.
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9002220465 900209 l9 l
gDR ADOCK 05000454 PNU l
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. -.. 'y, To establish the thimble tube wear acceptance criteria, a finite element structural analysis was utilized to evaluate the stresses in a worn bottom mounted instrumentation thimble tube. The wear scar geometry was assumed to be a flat bottom scar localized on one side of the thimble, which was consistent with the eddy current calibration standard.
It was determined that a sixty percent (60%) maximum wall is acceptable in accordance with ASME Code material allowables, therefore, a wall loss criteria of 60% was adopted.
It should be noted that this wall loss criteria of 60% is applicable for Byron /Eraidwood Stations Units 1 and 2 since the analysis was bounding for all four units. The wear scar calibration standard used for Byron Unit 1 inspections varied from the wear scar standard assumed by the analysis, however, it was verified that the 60% wall loss criteria was still applicable.
Attachment A contains the results of the first inspection of the Byroa bait 1 thimble tubes. Full length eddy current examinations were performed on 57 Incore Thimble Tubes and were completed by February 1, 1990.
The 58th incore thimble tube was obstructed by a cleaning tool and was not inspected. However, it has been removed and will be replaced with a new tube. Of the 57 tubes inspected, five indicated wear at the Reactor Bottom Penetration Sleeve and one tube indicated wear at the Lower Core Support l
Plate. All six wear indication depths were less than 20% through wall. The I
L affected thimble tubes are therefore acceptable for continued use.
l This completes the response to Bulletin 88-09 for both Byron Units 1 and 2.
1 Please address any questions that you or your staff may have concerning this response to this office.
Respectfully, M
T. K. Schuster Nuclear Licensing Administrator j
cc A. B. Davis-P. C. Shemanski - NRR Resident Inspector - Byron 0668T/TKS:wj/2 1
-e Attachment A RESULTS OF BYRON UNIT 1 THIMBLE TUBE INSPECTIONS l
Eddy current examinetions were performed on the thimble tubes f rom the seal table to the thimble end at the top of the fuel bundle.
i Five (S) thimble tubes, E-9, M-7, L-13. H-2, and R-8, contained outer diameter wear indications at the sleeve in the reactor bottom thimble tube penetration. All five indications were less than 20% through wall with the largest depth being 9% through wall. Tube D-12 contained an 11% through wall wear indication at the Lower Core Support plate. A cleaning tool obstructed tube H-15 approximately 4 feet from the seal table and subsequently was not examined. This tube was later replaced. No tubes were replaced as a result of of the eddy current inspection.
The following is a summary of each thimble tube indicationt i
Iuhm Corm _Lacation 1_Thronsh_ Wall Location.
i 12 E-9 9%
RBP +0.0" 16 M-7 6%
RBP +0.0" 31 D-12 11 %
LCS +0.0"
+
32 L-13 6%
RBP +0.0" 34 H-2 5%
RBP +0.0" 44 R-8 8%
RBP +0.0" 43 H-15 OBS STE -4 ft Lower Core Support Plate LCS No Detectable Discontinuity NDD Obstructed Tube OBS Outer Diameter Indication ODI Reactor Bottom Penetration Sleeve RBP Seal Table End STE t
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March 17, 1989 l
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U.S. 11uclear Regulatory Commission E
ALLnt' Document. Control Desk washington, D.C.
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l Subject Byron Station Unit 2 Response-to IIRC Bulletin 88-09 L
NRC Docket tio. 50-455 References (a) NRC Dulletin No. 88-09, dated July 26, 1988 p
Dear Sirt i
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Reference (a) requested that addressees establish and implement an inspection program to periodically confirm incore neutron monitoring system thimble tube Integrity at Westinghouse designed nuclear power reactors.
In L
p accordance with Reference (a), this letter presents the details of the incore b
thimble tube inspection program (Action 1) and the results of the thimble tube
. inspections (Action 2.a) performed during the first refueling outage for Byron
. Unit 2.
The t.hlmble tube inspections are performed using eddy current methodology.- The inspections will be performed at every refueling outage.
l L
until sufficient data has been accumulated to generate a baseline and g
correintion for. thimble tube thinning. At that time, the inspection frequency will.be evaluated and may be adjusted as applicable.
It is expected that at least two inspections will be necessary to accumulate sufficient data before considering any change in inspection frequency.
l To establish the thimble tube wear acceptance criteria, a finite element structural analysis was utilized to evaluate the stresses in a worn bottom mounted instrumentation thimble tube. The wear scar geometry was assumed-to be a flat bottom scar localized on one side of the thimble, which was consistent with the eddy current calibration standard.
It was determined that.a sixty percent (60%) maximum wall loss is acceptable in accordance with APME Code material allowables, therefore, a wall loss criteria of 60% was adopted.
It should also be noted that this wall loss criteria (60%) will be applicable for Byron Unit 1 and Draidwood Station Units 1 and 2 since the
' analysis was bounding for all tour units.
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U.S. Nuclear Regulatory Commission March 17, 1989 All incore thimble tubes (58 total) for Byron Unit 2 were inspected from the seal table to the end of the thimble tubes.
Three thimble tubes recorded evidence of degradation.
The thimble tube at. core location "D3" exhibited a' wall loss indication of approximately 13% at the lower tie plate.
It is b311eved that the wall loss is caused by vibration induced f retting wear with the lower tie plate, however, cont.inued wear at this degraded area is not expected since all thimble tubes were slightly repositioned during the outage L
(due to a modification which was performed on the seal table).
The thimble tubes at core locations "Ill5" and "R8" er.hibited a wall loss indication of t
approximately 17% and 10%, respectively, between the seal table and the reacter vessel. The wall loss indications, which were typical of external defects, are believed to be preservice related and continued wear at the two degraded areas is not expected.
Based on these results, there is confidence
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that a thimble tube failure will not occur prior to the next refueling outage i
for Unit 2.
This completes the Byron Unit 2 response for Reference (a).
To the best of my knowledge and belief, the statements contained above are true and correct.
In some respect these statementia are not based on my personal knowledge, but obtained information furnished by other Commonwealth Edison employees, contractor employees, and consultants.
Such information has been reviewed in accordance with company practice, and I believe it to be r e li abit..
Please address any questions that you or your staff may have concerning this response to this office.
Respectfully, ft $!5F -
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M. 11. Richter Nuclear Licensing Administrator
/lb:5592k cci A.D. Davis Resident Inspector - BY Subscribed and Swor to before ge t.hjs O I' day
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