ML18139A380

Forwards History of Experienced Total & Partial Power Outages at Facilities,Per NRC 800509 Request

ML18139A380
Person / Time
Site:	Surry, North Anna
Issue date:	06/26/1980
From:	Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, Varga S Office of Nuclear Reactor Regulation
References
458, NUDOCS 8006300456
Download: ML18139A380 (4)

Text

e e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND,VIRGIN.IA 23261 June 26, 1980 Mr. Harold R. Denton, Director Serial No. 458 Office of Nuclear Reactor Regulation NO/RMT:ms Attn: Mr. Steven A. Varga, Chief Docket Nos. 50-280 Operating Reactors Branch No. 1 50-281 Division of Licensing 50-338 U. S. Nuclear Regulatory Commission License Nos. DPR-32 Washington, D. C. 20555 DPR-37 NPF-4

Dear Mr. Denton:

We have reviewed your letter of May 9, 19 80 in reference to the history of experienced total and partial power outages at Surry and North Anna Power Stations. The attached response summarizes that history and addresses the specific questions contained in the "Loss of Offsite Power Survey".

Very truly yours, Ii¥'

B. R. Sylvia Manager-Nuclear Operations and Maintenance Attachment cc: Mr. James P. O'Reilly Mr. Robert A. Clark, Chief Operating Reactors Branch No. 3

e e Attachment Page 1 RESPONSE TO "LOSS OF OFFSITE POWER SURVEYr1

REFERENCE:

NRC letter dated .May 9, 1980 from S. A_ Varga - Operating Reactors Branch No. 1.

A review of Surry' s experiences has been performed which indicated two partial losses of offsite power have been experienc*ed; there have been no complete losses of offsite power.

The following are the responses to the survey questinns:

A. Partial Loss of Offsite Power

1) HOW MANY CIRCUITS TO THE OFFSITE NETWORK ARE NOfilLA.LLY AVAIL-ABLE AND HOW r1ANY WERE LOST DURING THE EVEN,i?

CASE 1 - There are two independent circuits from off site trans-mission network available to energize the 4160 VAC and 480 VAC emergency buses - (two auto transformers which feed Bus 5 and Bus 6 respectively). Bus 5 was the only source lost>* this resulted in a loss of two reserve station service. transformers and a Unit 1 trip of the turbine and reactor.

CASE 2 - Initial conditions same as Case 1, except between event dates an additional source was added 1 transfo.rmer :/14, which was added to supply buses 5 and 6.

The entire Bus #2 cleared itself as a result of a fault on the ffa2 auto-transformer. The #4 transformer energized the 34 .5 Bus #6 automatically. There was no effect *on either operating unit ..

2) WHAT WAS THE CAUSE OF THE EVF.....NT?

CASE 1 - The Buses 5 and 6 were tied together through the TS62 Breaker. During testing on the LT-12 Breaker, the TS62 breaker was mistakenly left in auto; it should have been :in manual. When the LT-12 breaker was closed with its disconnects open, the breaker logic required the TS62 to open, thus de-energizing the Bus #5.

Case 2 - While closing the Hi side breaker of the #2 auto trans-former returning lightning arrestors to serv'.iice, a ground fault occurred. This opened all of the ffal auto transformer breakers.

e e Attachment Page 2

3) WHY DID THE OTHER LINES NOT FAIL WHEN SO:t1E DID FAIL?

Case 1 - The event occurred as a result of breaker logic - nothing failed.

Case 2 - The tripping scheme functioned as designed, protecting the reset of the distribution system.

4) WAS ANY VOLTAGE INCREASE OR DECREASE EXPERIENCED JUST PRIOR TO OR DURING THE OUTAGES? IF SO, PLEASE GIVE DETAILS: . LOWEST FREQUENCY REACHED, DECAY RATE, AFFECTS ON EQUIPMENT, OPERA-TION, ETC. .

CASE 1 - None CASE 2 - None

6) HOW LONG WAS POWER UNAVAILABLE FROM THE CIRCUIT?

CASE 1 - Approximately 45 minutes.

Case 2 - Power to the emergency buses was never interrupted.

7) DATE OF EVENT CASE 1 - June 9, 1974 CASE 2 - November 10, 1978 B. For Losses of All Offsite Power:

NOTE: There have been no such events at Surry.

Attachment Page 3 NORTH ANNA POWER STATION RESPONSE TO "LOSS OF OFFSITE POWER SURVEY" A thorough review of North Anna station records was conducted and it has been determined that no occurrences of the type mentioned in the survey have occurred.

I