L-94-295, Confirms That Util Replaced 15 Leaking Westinghouse Mechanical Tube Plugs in Rows 5 or Greater & Has Preventatively Replaced Only Two Mechanical Tube Plugs in Row 4 or Less,Per NRC Bulletin 89-001
| ML17309A760 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 11/25/1994 |
| From: | Sager D FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML17309A761 | List: |
| References | |
| IEB-89-001, IEB-89-1, L-94-295, NUDOCS 9411300195 | |
| Download: ML17309A760 (3) | |
Text
PR.IC)R.I TV (ACCELERATED RIDS PROCESSli REGULATORY INFORMATION DISTRXBUTXON SYSTEM (RIDS)
ACCESSION NBR:9411300195 DOC.DATE: 94/11/25 NOTARIZED: NO FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power
& Light Co.
AUTH.NAME AUTHOR AFFILIATION SAGER,D.A.
Florida Power
& Light Co.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
DOCKET 05000335
SUBJECT:
Confirmas that util has replaced 15 leaking Westinghouse mechanical tube plugs in rows 5 or greater
& has preventatively replaced only two mechanical tube plugs in row 4 ot less,per NRC Bulleting 89-001.
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VP TITLE: Bulletin Response 89-01 re Failure of Westinghouse Steam Gen.
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'R/'DE7EMEB NRR/DSSA RGN2 FILE 0 1 NRC PDR COPIES LTTR ENCL 1
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1 NOTE TO ALL"RIDS" RECIPIENTS:
PLEASE HELP US TO REDUCE iVASTE!CONTACTTHE DOCL'MENTCONTROL DESK, ROOM PI-37 (EXT. 504-2083 ) TO ELIAIINATEVOL'R NAiIEPROi!
DISTRIBUTIONLISTS I'OR DOCI..'MENTS YOI'ON"I'L'ED!
TOTAL NUMBER OF COPIES REQUIRED:
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Florida Power & Light Company, P.O. Box 128, Fort Pierce, FL 34994-0128 November 25, 1994 L-94-295 10 CFR 50.4 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.
C.
20555 RE:
St. Lucie Unit 1 Docket No. 50-335 NRC Bulletin 89-01 Westinghouse Steam Generator Tube Mechanical Plu s During a conference call with the NRC staff on November 14,
- 1994, Florida Power and Light Company (FPL) notified the NRC staff that FPL had identified 15 leaking Westinghouse steam generator mechanical tube plugs during the post cycle 12 St.
Lucie Unit 1 refueling outage inspection.
As a result of follow-up conference calls on November 15, 1994, and November 16, 1994, FPL committed to provide the near term corrective actions and the bases for continued safe operation of the facility with the remaining 489 Westinghouse mechanical tube plugs in both the hot leg channel heads.
This letter confirms that FPL has replaced the 15 leaking Westinghouse mechanical tube plugs in rows 5 or greater and has preventatively replaced the only two mechanical tube plugs in row 4
or less with ABB/CE welded tube plugs.
In addition, the attachment provides the NRC with a copy of the evaluation performed by FPL to determine the significance of the leaking Westinghouse tube plugs along with the initial plans for the remaining Westinghouse tube plugs.
e The Westinghouse tube plugs in both hot leg channel heads were fabricated from a single heat (NX2387) of Inconel 600.
Based on the 'estinghouse algorithm (WCAP-12244, Revision 3),
the recommended repair date for these plugs was 2004.
Westinghouse has reviewed the St. Lucie new data and concluded that the plug leakage was most likely due to axial or limited circumferential cracks above the expanded section of the plugs.
As a result, Westinghouse revised the algorithm which predicts when plug top release from primary water stress corrosion cracking (PWSCC) could occur. For St. Lucie Unit 1 the new predicted useful life remaining after the current outage is estimated to be 3.0 effective full power years (EFPY), or 2.25 fuel cycles.
There have been no plug top release events earlie'r than predicted by the Westinghouse algorithm.
The Unit 1 steam generators are scheduled to be replaced during the Spring 1998 as part of the post cycle 14 refueling outage.
g,"g f 1 O e) p an FPL Group company rp4iii00195 94ii25 PDR ADOCK 050003 ~5 Q
~prI'/l
Thy bases for continued safe operation with the remaining Westinghouse plugs installed continue to be valid for the following reasons:
1 ~
A plug top release event is unlikely to occur because cracking above the expander is expected to be axial or limited circumferential orientation.
2 ~
If a plug top release event does occur the plug top would not perforate the tube.
3 ~
4 ~
5.
The majority of the tubes with Westinghouse mechanical tube plugs were removed from service for preventative reasons.
Therefore, a plug top release event is not expected to cause a tube rupture.
Circumferential cracking is expected to occur below the expander prior to the occurrence of cracking above the expander.
Cracking below the expander willnot result in a plug top release.
It is unlikely that cracking below the expander will result in the bottom of the plug becoming a loose part.
The physical interference of the plug skirt and lower sealing lands with the inside diameter of the tube retains the bottom portion of the plug in the tube.
In addition Westinghouse reported that there have been no known occurrences of the bottom portion of the plug becoming a loose part.
Should a portion of the plug become a loose part, it is unlikely that it would migrate out of the steam generator.
the loose parts monitoring sensors on the steam generator should provide the necessary indication.
The remnants of the removed plugs are being forwarded to Westinghouse for evaluation.
FPL will provide NRC the long term plan for the remaining Westinghouse mechanical tube plugs within 60 days of startup from the current refueling outage.
Please contact us if there are any questions about this submittal.
Very truly yours,
.3k>.F D. A.
ger Vice esident St.
L ie Plant DAS/GRM cc:
Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant