ML19327B079

Provides Required Info Re Detailed Description & Implementation Schedule for Resolution of Facility Fault Current Problem for 6.9 Kv Unit Board Load Breakers.Mods Will Be Implemented Before Startup After Unit 2 Refueling

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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i - Q'. 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 ) Docket Nos. 50-327 . Tennessee Valley Authority ) 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 , 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. A f 8910250143 891019 1 PDR P ADOCK 05000327 FDC h0hp g 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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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  ? 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 i Soddy Daisy, Tennessee 37379 ? I I t h

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. , . ENCLOSURE

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1 Comm1tment' l t 1* i l Before startup after the Unit 2 Cycle'5 refueling outage TVA will install f ~ T instantaneous overcurrent relays on'the. Incoming breakers from the untt l

station service transformers. In 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 unacceptable load breaker damage occurs.  ;

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