ML20035F990
| ML20035F990 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 04/19/1993 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9304230186 | |
| Download: ML20035F990 (3) | |
Text
.
-10CFR50.55a(g)(5)(iii)
PHILADELPHIA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS
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955-65 CHESTERBROOK BLVD.
WAYNE, PA 19087-5691 c15) 6404000 STATION SUPPORT DEPARTMENT April 19, 1993 Docket No. 50-352 License No. NPF-39 U. S.
Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Limerick Generating Station, Unit 1 Relief Request for Performing Bolt Removal Requirements Gentlemen:
Attached for review and approval is Relief Request No. RR-20 for the Limerick Generating Station (LGS), Unit 1,
American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV)Section XI, Class 2 pressure retaining bolting joining the Residual Heat Removal (RHR) Heat Exchanger shell flange to the tube sheet and channel head flange.
Specifically, we-are requesting relief from visual examination of every bolt in the flange connection.
As a result of leakage identified at a bolted connection of the RHR Heat Exchanger shell and channel head flanges during an ASME Section XI pressure test, we are now required by the 1986 ASME Code Section XI to visually inspect each bolt.
- However, this would require complete disassembly of the heat exchanger.
Justification-for the relief is explained in the attached relief request.
If you have any questions or require additional information, please do not hesitate to contact us.
Very truly yours, f /d A
G. A. M nger, Jr., Director Licensing Section Attachment cc:
T. T. Martin, Administrator, Region I, USNRC w/ attachment N.
S.
Perry, USNRC Senior Resident Inspector, LGS w/ attachment M
9304230186 930419-PDR ADOCK 05000352
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Appendix A-20 Page I of 2
)l Riii IIII: RiiQUI!ST NO. RR-20 i
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IDIIN1II:lCATION OF COMPONiiNTS j
Class 2 Residual lleat Removal (RllR) lleat lixchanger 11111205, pressure retaining bohing j
joining the heat exchanger shell flange to the tube sheet and channel head flange.
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. II.
CODI! RiiQUIRiiMl!NTS 1: ROM WillCil RI!I.Il!F IS Rl! OUI!STliD l
i ASMli Section XI requires that when leakage is detected at a bo!Td connection during the conduct of a Section XI pressure test, the bolting shall be visually examined for degradation.
Relief is requested from the requirement to visually examine every stud in the connection, due to hardship associated with the removal of a number of the studs in this situation.
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i Ill.
IIASIS 1;OR Rlil ll!It During the perfonnance of the periodic ASMl!Section XI pressure test of the Residual.
Ileat Removal System, leakage was identified at the bolted connection joining me shell to r
channel head of the RilR lleat fixchanger (1I11i205). Due to the design of the subject heat exchanger, sixteen (16) of the sixty four (64) studs in the flanged joint cannot be removed without complete disassembly of the vessel. Disasseml.ly of this vessel would require substantial chrt, including cutting a minimum of two 20" diameter safety related pipes.
l The subject bolted connection is made up of sixty four,1-1/8" nominal diameter all thread studs (RNC 2), located around a bolt circle of 58-5/8" diameter. The stud material is SA-193-117, and the nut material is SA 194-211. livery fourth stud around the bolt circle (16 total), contains a threaded washer located inside the flanged joint, which precludes removal of these studs unless the triple flanged joint is completely disassembled.
The remaining 48 studs were removed for examination using the VT-1 examination method.
The load bearing threads on each end of the 48 studs showed no signs of degradation.
l llowever, because of a buildup of corrosion product in the non load bearing threads of the studs, a conclusive VT-1 examination of the thread root in this area was not possible.
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- Appendix A-20 Page 2 of 2 Rl!LIl!F RI!QUliST NO. RR-20 (CONTD.)
Several attempts were made at removal of this buildup, however radiological concerns precluded further processing of the studs.
Since the studs exhibited evidence of corrosion of the non load bearing thrrads, all 48 studs were replaced in kind. To quantify the' extent of degradation due to corrosion, the stud representing the worst condition, as detennined by visual examination, was selected for further cleanup. Following this additional cleanup, the areas of degradation.wcre measured to determine the extent of material loss. Additionally, the cleaned stud was examined by a 1evel til visual examiner to determine the condition of the therad root areas. The cumination found m, adverse surface condition in this area. Measurements indicated that material loss was concentrated at the major diameter of the threads, with minimalloss at the minor diameter.
Analysis, considering the conditions described almve, indicated that structural integrity of the bolted joint would be maintained, considering potential degradation of the studs which were not removed. Therefore, continued, safe operation of the RilR lleat IIxchanger will not be compromised by this condition.
IV.
ALTERNATI1 PROVISIONS Forty eight of the original sixty four studs have been replaced, since all removed studs exhibited varying degrees of corrosion. Measurement and examination of tne corrosion indicated that degradation, resulting from the corrosion, has had little impact on.the structural capaNiities of the bolting. Nevenheless, an analysis has been perfonned to confinn the structural integrity of ihe leited connection considering potential degradation of the studs which were not replaced. Additionally, the 16 original studs will be removed and evaluated in conjunction with a planned modification for tube bundle replacement on this heat exchanger. This modification is currently planned for implementation during the fifth refueling outage (1ROS), scheduled for the first quarter of 1994.
Although some leakage continues at the bolted connection, a monitoring program has been -
put in place to monitor the rate and nature of the Icakage to assure that the basis and conclusions of the structuralintegrity evaluation are not invalidated.
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