ML20070D348
| ML20070D348 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/26/1991 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-088, 91-88, NUDOCS 9102280213 | |
| Download: ML20070D348 (2) | |
Text
II Vueoixir hi:rTuic Ann Powi:n Co.wivAxy It acussown,Viuotuir ununt February 26,1991 United States Nuclear Regulatory Commission Serial No.
91 088 Attention: Document Control Desk NL&P/JBL:jmj R0 Washington, D.C. 20555 Docket No.
50 338 License No.
NPF 4 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMFAliY NORTH ANNA POWER STATION UNIT 1 STEAM GENER ATOR CATEGORY C-3_',NSPECTION REL iS REQUEST FOR STARTUP APPROVAL North Anna Power Station Unit 1 sliJtdown on January 11, 1991 for a scheduled refueling outage. During the refueling outage eddy current examinations of the steam generator tubes were conducted as requireo by the augmented inservice inspection program described in the Technical Specification 4.4.5.
The _results of the steam genereur inservice inyections have been classified as Category C-3 (as cf m 'in Tocht:- 9paificatiren 4.4.5.2) for each of the unit's three steam generators,
.a., 3reater that. 1% of the inspected tubes are defective and require plugging. In ac:ardance with the requirements of Technical Specification 4.4.5.5.c, prompt noilfication of the inspection results was made to the NRC pursuant to 10 CFR 50.72. The required notifications were made on January 30,1991 for the "B" steam generator and on February 8,1991 for the "A" and "C" steam generators. A subsequent Licensee F >ent Report (LER) will be submitted pursuant to 10 CFR 50.73 providing further description of the investigations conducted to determine the cause of the tube degradation and any additional corrective measures to be taken to prevent recurrence.
The purpose-of this ietter is to request NRC approval to return to power operation -
.following this refueling outage. in this case, return to power operation is delined as-entry into Mode 4, i.e., compliance with Technical Specification 3.4.5 requires steam generator operability prior to entry into Mode 4. We are presently scheduled to enter Mode 4 on March ( 1991. As specified in Table 4.4-2-of the North Anna -Unit 1 Technical Specifications, NRC approval is required prior to operation whsn the lospection results of any two of the steam generators are classified as Category C 3.
- The insoection results and a technical evaluation of those results were discussed in dehd at our February 26,1991 meeting. Also, the basis for our determination that appe e for resumption of power operation should be grar*~f was included in the -
Virginia Electric and Power Company and Westinghouse Electric Corporation (Reference Letter Serial No. NS NRC 91-2571) presentation material provided at that meeting.-
4l4 9102290213 910226 r 1R ADOCK 0500 8
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In summary, the steam generator tube bundle integrity has been re established by tube plugging and, where necessarv, tube stabilizers installod. We have evaluated growth rates of the circumferential indications in the top of tubesheet region and the circumferential and axial indications at the tube support plates. The projected end of-cycle average crack sizes have been determlied acceptable with respect to the structural performance margin (burst capability criteria) established per Regulatory Guide 1.121.
The Technical Specification surveillance requicement for primary to secondary leakage monitoring will continue to be applicable.
In addition, the conservative primary to secondary administrative leakage limits (50 god maximum in any individual steam generator) will continue to be maintained.
Based on the information available at this time, the inspection results do not preclude full cycle operation. However, the tube pull results and assessments are needed to further substantiate our final conclus!on. These assessments include the potential for i
burst pressure reduction due to combined axial plus circumferential degradation, the potential for crack propagation of circumferential cracks due to tube vibration, and the potential leakage during a postulated steam line break for the end of cycle crack distribution. The NRC will continue to be kept informed of the progress on tube pull results.
Should you have any questions or require additional information, please contact us.
Very truly yours, AoI W. L. Stewart Senior Vice President - Nuclear cc:
United States Nuclear Regulatory Commission Region 11 101 Marietta Street, N.W.
Suite 2900 Atlanta, GA 30323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Power Station l