ML20210H869

Provides Suppl Info Re Analysis Performed by TVA to Support Reliability of Offsite Power Sys,Per 970710 Telcon

ML20210H869
Person / Time
Site:	Sequoyah
Issue date:	08/05/1997
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-M93319, TAC-M93320, NUDOCS 9708140220
Download: ML20210H869 (6)

Text

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Q{b IUA tenn.sm v.w Asun, rw ona tw un s<xioy.o sy tenresseo 3r379 August 5, 1997 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SON) - SUPPLEMENTAL INFORMATION TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RfLIABILITY OF OFFSITE POWER SYSTEM (TAC NOS. M93319 AND M93320)

Reference:

TVA letter to NRC dated June 2, 1997, on the above subject This letter provides supplemental information regarding analysis that has been performed by TVA to support the reliability of the offsite power system. The enclosed information supplements the referenced response and is provided as requested by NRC during a telephone call on July 10, 1997.

NRC issued Inspection Report Numbers 50-327/93-02 and 50-328/93-02 on February 23, 1993, regarding the reactive team inspection of the December 31, 1992, dual unit trip at SQN. This report included Unresolved Item (URI) 50-327, 328/93-02-04 requiring that TVA submit information regarding the_ modifications to the offsite power system, supporting calculations, latest grid load study, and application of Technical Specification requirements for loss of switchyard equipment. TVA informally provided this information to NRC.

NRC Region II did not close this URI. Instead they issued

' Task Interface Agreement (TIA)94-021. This TIA requested i a 1

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9708140220 97G006 PDR ADOCK 05000327 P PDR. e

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U J. Nuclear Regulatory Commission

.Page 2 August 5, 1997 review to. answer _ questions regarding the acceptability of the SON design to handle situations that require or result in the removal of the 500-kV to 161-kV intertie transformer and maintain an acceptable offsite power system and safe shutdown capability. The TIA also requested a response to a question regarding the acceptability of the SON Technical Specifications with respect to necessary actions for the loss of the 500-kV to 161-kV intertie transformer.

On March 27, 1996, the Office of Nuclear Reactor Regulation issued to TVA a Request for Additional Information (RAI). In this request NRC asked for information that verifies the voltage at the safety busses, during a trip of SON Unit 2 resulting from a loss-of-coolant accident, does not go below relay setpoints for an unacceptable duration. This is a duration that would result in the transfer of the safety buses from the offsite power system to the emergency diesel generators. TVA provided this information on July 17, 1996.

On January 17, 1997, NRC issued a second RAI that requested specific analysis results of the design basis events that are described in the SON Updated Final Safety Analysis Report (UFSAR). This RAI also requests information regarding

-the provisions in place to ensure control room personnel at SON are kept informed of the capability of the offsite power system. TVA provided this information on June 2, 1997.

On July 10, 1997, TVA and NRC held a telephone call to discuss one outstanding issue from the June 2, 1997, RAI response. This issue involved transient voltage analysis that was not performed in the TVA load studies for the FSAR described event. This event is a trip of' Unit 2 with a full load rejection of the other unit. TVA explained that the cases that were evaluated by transient voltage analysis were more limiting and bounded the UFSAR described event. NRC requested that this information be submitted to-the staff.

JrVA has elected to perform a transient voltage analysis of the event to ensure that there is no misunderstanding that this case results in acceptable voltage response of the offsite power system. This information is contained in the enclosure to-this letter.

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U.S. Nuclear Regulatory Commission Page 3 August 5, 1997 The URI was closed by NRC Region II in Inspection Report Numbers 50-327/97-06 and 50-328/97-06, dated July 28, 1997.

TVA considers this response to be adequate to resolve the TIA and concerns regarding the adequacy of the TVA offsite power system to support SON operation and accident mitigation functions.

Please direct questions concerning this issue to me at (423) 843-7170 or J. D. Smith at (423) 843-6672.

Sincerely, Pe 1 Salas Site Licensing and Industry Affairs Manager Enclosure cc: See page 4

a U S. Nuclear Regulatory Commission Page 4 August 5, 1997 cc (Enclosure):

Mr. R. W. Hernan, Project Manager Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlarta, Georgia 30303-3415

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ENCLOSURE SUPPLEMENTAL INFORMATION TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIABILITY OF OFFSITE POWER SYSTEM This enclosure provides the basis that supports adequate offsite voltage recovery for a loss of coolant event on Unit 2 and a full load rejection of Unit 1 with the 500-161-kV intertie transformer bank out-of-service pre-event. Attached is a transient stability simulation voltage plot of this case. SON-Grid-Study-004 has been revised to include this case. There is very little transient dip-in voltage and no loss-of-voltage or undervoltage relay setpoints are challenged by this case.

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