ML20084H834

AO BFAO-7424W:on 740403,unit Tripped Due to Transmission Interruptions.Caused by Tornados.One 161-kV Line Lost.No Known Corrective Actions

ML20084H834
Person / Time
Site:	Browns Ferry
Issue date:	04/19/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-BFAO-7424W, NUDOCS 8305060012
Download: ML20084H834 (3)

Text

VAL / AUTHOAITY On TT!'/

TENNESSEE CHATTANOOGA, TENNESSEE :i 37401 iJ, , ! .' -

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April 19, 1974 f.,s.' . '- 'i.. .' l . s. .

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^  :): Y l'r. John F. O'Learg, Director D L-h' Directorate of Licensing N 0 Office of Regulation g U.S. Atomic 2nergy Cornission..

Washington, DC 20545

Dear Mr. O' Leary:

TEITIESS23 VALLTI AUTEORIW - 3R0iHIS FERRY liUCLEAR PL3 LIT UNIT I'ACILITI OP3RtcTII:G LICIIISE DPR AB:!OR?LU, DOC:GT II0. 50-259 -

OCCURRI;CD REPORT B7AO-7424W Tne enclosed report is to provide details concerning a tornado sfaich resulted in plcnt shutdo::n end loss of one 161-h7 line. This eventd occurred on 3rouns Ferry 1:ncletr Plant unit 1 on April 3,1974, Guide c.rl 1!i6, is subnitted in recordr.nce uith Appendix A to Regulator /

Revision 1, October 1973 Very la ul: 4:; ara,

= TEIEESSE3 VALL Y AUTIiORITI

. W E. F. Thonas Director of Pouer Production Enclosure CC (2nclosure):

Fr. IIornen C. Ibccley, Director Region II Regulr. tor / Operations Office, US!.EC 230 Pcechtree Street, IT.I. , Suite 818 Atlenta, Georgia 30303 I p g

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u ABHoluiG OCCURREUCE REPORT

-Report No.: BFAO-74247 Report De.te:' April 19, 1974

' Occurrence Date: . April 3, 1974

- Facility: 3rowns Ferry Nuclear Plant unit 1 Identification of Occurrence

~ Tornado resulting in plant shutdown and loss of one 161-kV line.

Conditions Prior to Occurrence The reactor was in' operation at approximately 92-percent power suppAying electricity to the TVA system over five 500-hv transmission lines. Two 161-hv transmission

- lines which supply the plant were also energized.

Descriution~ of Occurrence At approximately 6:15 p.m. on April 3, the plant was notified that a tornado warning was in effect for the area. At this time, new fuel inspection operations were terminated on the refueling floor and the fuel-hendling crew uns removed from the refueling floor.

At approximately 6:53 p.m., the unit tripped as a result of transmission interruptions resulting from tornadoes in the area. By correlating the eventsava7tm from the elecLilee.1 w qucntic.1 cvents recorder and the reacter se r en+Aal recorder, it een be seen that the Trinity Substation end the Trinity lines received the first'densge. Doth the 500-kV line end the -161-hV line from Trinity tripped ear 3,y in the series of events. Both reclosed and tripped cgain. .

The main' generator enperienced a generator overcurrent relcy operetion in the 3" phase either as a result of a breder failure on the Trinity line or as a result of faults elsewhere on the 500-h7 system. The reactor scrcrned by action of the loed' reject relry. All of the reactor snfeguard and auxiliary ecuipment perforned

. properly during the trip cnd resulting transient. The nain steen isolation vr.lves recained open, ste. tion-service electrical pouer was alucys available from the Athens 161-kV line, and the main condenser was available as a heat sin':.-

During the electrical disturbances and related automatic-transfer of inplant electrical boards, the "A" rnd "B" diesels stcrted automatically by an undervoltage condition which appears to have lasted long enough (> 1-1/2 seconds) to start the .

diesels, but not long enough (> 5 seconds) for the diesels to tie onto their boards. "C" and "D" diesels vere menun11y started to be available should a complete loss of plant offsite power ' occur. There was no release of radioactive

~s team or material as a result of the occurrence. The only plant denage sustained

-was the failure of one 500-hV cuitchyard breaker due to a trcnsmission line fault.

Initially, the reactor was held in the hot shutdoun condition at near rated L pressure until the status of the 500-hV system becene known. The unit was thca L placed in.the-cold shutdown condition.

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Designation of f.nnarent Cause of Occurrsnec s The single apparent cause of the occurrence was several tornadoes which passed through the Tennessee Valley area. Subsequent investi6 ation revealed extensite demage to four of the five operable 500-hV lines and to one of the two 161-hV lines. Several touers were doun on each line.

I.nalysis of Occurrence The plant site was not in the direct path of try of the torne.does. Offsite 7m.er was c1weys :available by one 161-hV line, and ell' plent emergency pouer diesel generators . started properly when actucted either automatically or menually.

Corrective Action .

< There is no knoun corrective r.ction to be $e. ken- to prevent repe'tition of this type occurrence. , _. ,

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