ML20073K106
| ML20073K106 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/03/1994 |
| From: | Zeringue O TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9410110013 | |
| Download: ML20073K106 (5) | |
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October 3, 1994
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i U.S. Nuclear Regulatory Commission A11N: Document Control Desk Washington, D.C. 20555
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Gentlemen:
In the Matter of
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Docket No. 50-327 Tennessee Valley Authority
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SEQUOYAll NUCLEAR PLANT (SQN) - REQUEST FOR DISCRETIONARY ENFORCEMENT FOR UNIT 1 TECHNICAL SPECIFICATION (TS) 3.8.2.1, ACTION b, FOR VITAL INVERTER 2-I This letter serves to document the basis for TVA's verbal request on October 2, 1994, for discretionary enforcement for Unit 1 TS 3.8.2.1, Action b, for Vital Inverter 2-I.
During maintenance on Vital Inverter 2-I, problems were encountered with the alternating-current output breaker and a subsequent replacement breaker. As a result, the 24-hour allowed outage time provided by TS 3.8.2.1, Action b, was anticipated to be exceeded by approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. A review of the Unit 1 and common loads potentially affected by the out-of-service 2-I vital inverter indicates that there is no safety consequences to Unit 1 operation (see enclosure for additional details).
This request has been PORC (Plant Operations Review Committee) approved.
In order to allow adequate time to complete the installation and testing of Vital Inverter 2-1, 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> has been requested in addition to the
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24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided by TS 3.8.2.1.
Without the additional time, Unit i l
would have begun a shutdown at 0641 Eastern daylight time on October 2, 1994.
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9410110013 941003 PDR ADOCK 05000327
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i U.S. Nuclear Regulatory Commission Page 2 October 3, 1994 Please direct questions concerning this issue to J. D. Smith at (615) 843-6672.
Sincere 7~ /
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Ji Zeringue Acting Site Vice President Enclosure cc (Enclosure):
Mr. D. E. LaBarge, Ptoject Manager U.S. Nucienr Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 f
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ENCLOSURE Vital Inverter 2-I Discretionary Enforcement for Technical Specification (TS) 3.8.2.1 Eatkgtnund During a return to service following routine maintenance on Vital Inverter 2-1, the 225-amp, molded case, alternating-current (ac) output breaker tripped open and then failed to close (note that while it is labeled as an output breaker, the actual components consist of a switch inline with two fuses to protect inverter circuitry). The suspected cause for the failure to close is failure within the operator mechanism.
The available onsite replacen;ent breaker subsequently f ailed during preinsta11ation testing. A replacement breaker was obtained from Watts Bar Nuclear Plant. The estimated time to replace the breaker and complete the postmaintenance test was 1800 Eastern daylight time (EDT) on October 2, 1994. TS 3.8.2.1, Action b, was entered at 0641 EDT on October 1.
This action requires the vital inverter to be returned to service within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in HOT STANDBY within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Before the failure of the ac output breaker to close, a direct current input breaker was also replaced. The new de input breaker's auxiliary contacts were not wired the same as the old breaker.
Troubleshooting of this problem delayed the inverter return to service by four to five hours.
The combination of breaker problems will result in the outage time exceeding the TS allowable.
IS_ Compliance TS 3.8.2.1, Action b, allows a vital inverter to be inoperable for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> before proceeding to a shutdown condition.
The 24-hour period expired at 0641 EDT on October 2. Final postmaintenance testing was estimated to be completed at approximately 1800 EDT on October 2.
To allow for adequate time to complete additional inspection and testing of Vital Inverter 2-1, 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> was requested in addition to the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided by TS 3.8.2.1, to prevent unit shutdown.
Safe.tv ConEnquentes The af fected vital inverter serves the 120-volt (V) ac vital Instrument Power Board (IFB) 2-I.
The 2-I IFB was energized to the alternate feed when the 2-1 vital inverter was removed from service. The alternate feed is not considered a qualified source only because power is interrupted while the electrical boards are being loaded on the diesel generators in the event of loss of ac.
TVA has reviewed the loads served by the 120-V ac vital IFB 2-I and has identified no components that could impact Unit 1 operation. Although initial reviews identified some components associated with systems common to both units (e.g., essential raw cooling water and component cooling system), further review shows that the specific components will only affect U3it 2 operation given the current plant configuration.
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. In' addition, a nonqualified output breaker has been installed to allow the inverter to remain warm during the extended outage. Should a loss of ac event occur, Operations will close the ac output breaker for Vital Inverter 2-I.
The additional allowed outage time to TS 3.8.2.1 has been determined to be of no safety significance. In addition, the risk associated with shutting Unit 1 down is judged to be greater than the risk associated with the additional unavailability of Vital Inverter 2-I. These risks include the power system transfer associated with unit shutdown and the additional management challenges associated with shutting the unit down.
Accordingly, the discretionary enforcement will not result in a significant increase in the probability or consequences of a previously evaluated accident, will not create the possibility of a new accident, and will not result in a significant reduction in the margin of safety.
Also, the action does not involve an unreviewed environmental question because it does not increase any adverse environmental impacts, change effluents or power levels, or result in unreviewed environmental matters.
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U.S. Nuclear Regulatory Commission Page 3 October 3, 1994 RHS:JDS:PMB Enclosure cc (Enclosure):
M. J. Burzynski, DSE 1A-SQN E. S. Christenbury, ET 11H-K R. F. Driscoll, OPS 4A-SQN K. N. Harris, LP 3B-C R. W. Huston, BR 4G-C J. B. Kinney, MR 2C-C T. J. McGrath, LP 3B-C M. O. Medford, LP 3B-C D. E. Nunn, Jr., LP 3B-C E. J. Vigluicci, ET 10H-K