ML19327B079
| ML19327B079 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/19/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8910250143 | |
| Download: ML19327B079 (3) | |
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 3740' SN 157B Lookout Place 00T 191989-U.S. Nuclear Regulatory Commission L
ATTN: Document Control Desk i
Washington. 0.C.
20555 Gentlemen:
In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - FAULT CURRENT PROBLEM FOR THE 6.9-KILOVOLT (kV) t UNIT BOARD LOAD BREAKERS
Reference:
TVA letter to NRC dated August 4, 1989, "Sequoyah Nuclear Plant -
Fault Current Problem for the 6.9-Kilovolt (kV) Unit Board Load Breakers" v
l In.the referenced letter, TVA committed to provide a detailed description and the implementation schedule for the resolution of SQN's fault current problem l
for the 6.9-kV unit board breakers.
This letter provides the required information, j
The 6.9-kV unit boards at SQN are equipped with ITE Imperial Corporation 7.5HK500 breakers that have a one-time interrupting capability of i
550 megavoltamperes (43,829 amperes (A) at a maximum system voltage of 7.245 kV). The ma.imum calculated fault current for these boards is 49,455 A at 7.245 kV. This ;ondition is for a three-phase, bolted fault in close proximity to the botrd and would only occur when the boards are unit-connected.
l To correct the probitm, TVA will install instantaneous overcurrent relays on the incoming breakers from the unit station service transformers so that a 3
high-level fault on a load feeder would be interrupted by the incoming
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breaker.
The incomitg breakers have adequate Interrupting capability to l
ensure that maximum ;hree-phase, bolted faults are properly cleared.
In i
addition, the overcurrent relays or relay settings on the load breakers will be modified as necessary to ensure that fault currents above the load breaker interrupting capability will be cleared by the incoming breaker before
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unacceptable load breaker damage occurs.
TVA will implement the required modifications before startup after the Unit 2 Cycle 5 refueling outage.
The probability of a close, three-phase, bolted fault while the boards are unit-connected is low.
This issue is not a nuclear safety concern.
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8910250143 891019 h0hp PDR ADOCK 05000327 1
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An Equal opportunity Employer 1
00T i n 1989
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U.S. Nuclear Regulatory Commission A summary statement of the commitment is provided in the enclosure.
Please j
direct questions concerning this issue to Kathy S. Whitaker at (615) 843-7748.
Very truly yours, TENNESSEE VALLEY AUTHORITY
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Man &ge Nuclea i. censing l
and Regulatory Affairs Enclosure cc (Enclosure):
Ms. S. C. Black, Assistant Director for Projects TVA Projects Division i
U.S. Nuclear Regulatory Commission One White Flint, North-11555 Rockville Pike l
Rockville, Maryland 20852
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i Mr. B. A. Hilson, Assistant Director i
for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 j
NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 i
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ENCLOSURE 1
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Comm1tment' l
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f Before startup after the Unit 2 Cycle'5 refueling outage TVA will install
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T instantaneous overcurrent relays on'the. Incoming breakers from the untt l
- station service transformers.
In addition, the overcurrent relays or relay
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settings on.the load breakers will be modified as necessary to ensure that fault currents above the load. breaker interrupting capability will_be cleared by the incoming breaker before unacceptable load breaker damage occurs.
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