ML19318A156

Responds to NRC 800505 Ltr Re Loss of Offsite Power Events. Details of 750222,1205 & 800407 Events Indicate Weather Conditions Were Responsible on All Occasions.Only Momentary Losses of Power Were Experienced

ML19318A156
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/11/1980
From:	Trimble D ARKANSAS POWER & LIGHT CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
1-060-08, 1-60-8, 2-060-10, NUDOCS 8006180528
Download: ML19318A156 (3)

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. ARKANSAS POWER S LIGHT COMPANY POS CMICE BOX 551 UTTLE RJCK. ARKANSAS 72203 (501) 371-4000 June 11, 1980 1-060-08 2-060-10.

Director of Suclear Reactor Regulation ATTN: Mr. R. W. Reid, Chief

. Operating Reactor Branch #4 U. S. Nuclear Reculatory Commission Washington, D. C. 20555 i

Subject:

Arkansas Nuclear One-Unit 1&2 s

" Docket No. 50-313 & 50-368 License No.-DPR-51 & NPF-6 Loss of Offsite Power Events (File: 1510,2-1510)

' Gentlemen:

In response to Mr. Reid's letter of May 5,1980, the following information is provided cor.cerning loss of offsite power events at Arkansas Nuclear One.

Very truly yours, b7Z $5 i -

David C. Trimble M Manager, Licensing DCT:JTE:sh i

I

$0.061807 8 9 vee u- s- m Ties sysTe

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i EVENTS:

February 22,'1975; December 5,1975; and April 7,1980. It should be understood that our records were based on loss of offsite power events

.- which significantly affected plant operation. Therefore other events may i have occurred that are not.in our records because they did not affect plant operations. i Attached is a short description of each event with answers to NRC ques-tions. Some questions were answered without hard data because records 3

concerning the information were not available. l EVENT DATE: February 22, 1975.

EVENT DESCRIPTION: At 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> the 161 KV ANO to Morrilton East trans-I mission line relayed out and locked out. Later it was energized-from ANO but was deadended and only feeding from ANO. At 1608 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.11844e-4 months <br /> three towers were blown down by a tornado on the Mabelvale-ANO 500 KV line and that line was lost for several days. Oscillograph traces indicate

.that the fault was cleared in 3 cycles; then 29 cycles later one ACB

} was automatically released on the fault. Again the ACB relayed out in 3S' cycles. .When this line fault occurred the 500 KV bus voltage dropped to very near zero. This in turn caused the inplant voltage to sag. The inplant low voltage condition caused a reactor trip which tripped the generator lock out relay. This relay tripped all four 500 '

l KV ACB's open, leaving only the 161 KV Russellville East line to supply ANO.

Answers to Questions: -

. #1. This event occurred prior to the completion of the ANO-Mayflower i 500 KV transmission line. At that time four circuits were nor-mally available; three circuits were lost.

} #2. See event description.

l #3. See' event description.

t 4

1. 4. Detailed information is not available, but due to the nature of I -the event, it is not likely that any voltage perturbations occurred prior to the event.

! - #5. Detailed 'information is not available, but due to the nature of a the event, ' frequency probably was unaffected until the event it-

.self, then frequency fluctuations, both high and low were exper-ienced.

-#6. Detaile'd information is not available, but records: indicate that power was- unavailable for approximately 5 minutes, i

j EVENT DATE: December 5, 1975 EVEtiT DESCRIPTION: At 1819 hours0.0211 days <br />0.505 hours <br />0.00301 weeks <br />6.921295e-4 months <br />, a lightning induced interruption occurred on the 161 KV Morrilton East transmission line with instantaneous re-closing of breakers 1215 and 1218. There was a voltage and frequency dip associated with the lightning strike.

Answers to Questions:

1. 1. This event occurred prior to completion of the AND-Mayflower 500 KV transmission line; at the time of the event, four circuits were normally available. One circuit was lost only momentarily.

1. 2. See event description.

1. 3. See event description.

1. 4. There was no voltage perturbation experienced prior to the lightning strike.

1. 5. There was no frequency perturbation experienced prior to the light-ning strike.

1. 6. Only a momentary interruption in power was experienced.

I EVEf1T DATE: April 7, 1980 EVENT DESCRIPTION: Loss of all of fsite power occurred. At 1728 hours0.02 days <br />0.48 hours <br />0.00286 weeks <br />6.57504e-4 months <br />, the 500 KV line to Ft. Smith was lost due to tornado damage and 57 minutes later the 500 KV line to Mabelvale was also lost due to tornado damage.

At 1848 hours0.0214 days <br />0.513 hours <br />0.00306 weeks <br />7.03164e-4 months <br /> ANO Units I and II tripped on loss of all offsite power.

Due to relay action in the switchyard the startup transformers were temporarily unavailable although power was available via the 161 KV transmission system.

Answers to Questions:

1. 1. Offsite power was off 22 minutes. However, there was power avail-able through the 161 KV transmission system during this time, but was not used since both units were stable on emergency power.

Maintenance personnel were dispatched to confirm that the startup transformers were undamaged prior to being re-energized.

1. 2. Loss of offsite power and turoine trip was simultaneous.

1. 3. Power recovery was not accomplished within 10 minutes, but could have been accomplished manually in that time frame.

1. 4. Detailed information is not available. However, there were volt-age perturbations during earlier line failures and lightning strikes. However, these were not sustained for long periods.

1. 5. Frequency perturbations were experienced prior to and during the event when lightning strikes occurred but these were not for sus-tained periods.