ML18033B327

Forwards Info to Resolve Restart PRA Commitments,Per NUREG-1232 (SER on Nuclear Performance Plan).Util Will Confirm Adequacy of RHR Pump W/Rhr Motor Cooler Unavailable to Meet short-term Pump Combination Requirements

ML18033B327
Person / Time
Site:	Browns Ferry
Issue date:	05/24/1990
From:	Wallace E TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RTR-NUREG-1232 TAC-63178, NUDOCS 9005310120
Download: ML18033B327 (8)

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t UTION DEMONSTPATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9005310120 DOC.DATE: 90/05/24 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION WALLACE,E.G. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document. Control Branch (Document Control Desk)

SUBJECT:

Forwards resolution of restart PRA commitments made in 890615 ltr.

DISTRIBUTION CODE: D030D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: TVA Facilities Routine Correspondence NOTES:1 Copy each to: S.Black,D.M.Crutchfield,B.D.Liaw, 05000260 R.Pierson,B.Wilson RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL LA 1 1 PD 1 1 ROSS,T. 1 1 INTERNAL: ACRS 1 1 NUDOCS-ABSTRACT 1 1 OC LE+3 1 0 OGC/HDS2 1 0 G E 1 1 EXTERNAL: LPDR 1 1 NRC PDR 1 1 NSIC 1 1 NOTES: 5 5 NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI TOTAL NUMBER OF COPIES REQUIRED: LTTR 16 ENCL 14

TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 5N 157B Lookout Place IIe S< F9~0 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of Docket No. 50-260 Tennessee Valley Authority BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 2 PROBABILISTIC RISK ASSESSMENT (PRA)

RESTART COMMITMENTS (TAC 63178)

The purpose of this submittal is to provide the resolution of the restart PRA commitments which were made in TVA letter to NRC, dated June 15, 1989. These commitments- are also reflected in Section 3.9 of Supplement 1 to the Safety Evaluation Report on the BFN Nuclear Performance Plan NUREG 1232, which was sent by letter from NRC to TVA, dated October 24, 1989.

TVA's June 15, 1989 submittal contained two restart commitments. The background of the issue, the commitments, and a description of the.ir.

resolution is provided in the Enclosure. There are no commitments contained in this letter. It is TVA's understanding that this submittal completes all outstanding actions associated with TAC 63178. TVA requests the Safety Issues Management Systems be updated to reflect this, completion. If you have any questions, please telephone Patrick P. Carier, Manager of Site Licensing, at (205) 729-3570.

Very truly yours, TENNESSEE VALLEY AUTHORITY E. . Walla e, Manager Nuc ear Licensing and Regulatory Affairs Enclosure cc: See page 2 900531012 0 900524

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U.S. Nuclear Regulatory Commission MAY 84 1990 cc (Enclosure):

Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One Hhite Flint, North 11555 Rockville Pike Rockville, Maryland 20852 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35609-2000 Mr. B. A. Hilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NN, Suite 2900 Atlanta, Georgia 30323

~ y Enclosure DISCUSSION OF PROBABILISTIC RISK ASSESSMENT (PRA) RESTART COMMITMENTS The background of the specific PRA issue, the restart commitments and a description of their resolution is provided below:

Background:

NRC held an audit of the Browns Ferry PRA in November 1988.

This audit resulted in a finding based on the assumption contained in the BFN PRA that a single failure of an electrical board could disable one loop of Low Pressure Coolant Injection (LPCI) and one loop of Core Spray due to the loss of power to the Residual Heat Removal (RHR) pump motor coolers and the room cooler for the Core Spray Pumps. If this single failure disabled the affected pumps as assumed in the PRA, the loss of the remaining LPCI loop due to a recirculation line break would result in only one loop of Core Spray being available for core cooling. This would not meet the minimum requirements for core cooling pumps currently specified in BFN Final Safety Analysis Report (FSAR) Table 6 '-2.

The response to this concern is contained in TVA's June 15, 1989 letter to NRC. In summary, the minimum pump requirements specified in FSAR Table 6.5-2 are short-term (less than 10 minutes) requirements. The long-term core cooling pump requirements are not specified in the FSAR Table. The design calculation on which the FSAR is based ind,i.cate.s that the.

long-term pump requirements are met by one loop of Core Spray providing core injection and one loop of RHR aligned for cont:ainment cooling.

Commitment: TVA will confirm the adequacy of the RHR pump with the RHR motor cooler unavailable to meet the short-term pump combination requirements.

T Resolution: The Environmental Qualification (EQ) program for BFN has evaluated the RHR pump motors for operation at elevated temperatures resulting from design basis accidents including high energy line breaks outside containment. This evaluation demonstrates operability of the RHR pump motors at peak ambient temperatures up to 145 degrees Fahrenheit. The worst case winding temperature is expected to occur 90 minutes after the pump has started when the ambient temperature is 144 degrees Fahrenheit and the motor has reached a full winding temperature rise of 1 19 degrees Fahrenheit. This results in a winding hot spot temperature of 263 degrees Fahrenheit. This condition has been evaluated in the environmental qualification documentation package for the RHR pump motors and was determined to be acceptable.

Page 2 of 2 Resolution: The environmental conditions in the RHR pump room during the (Continued) first ten minutes after a design basis Loss of Coolant Accident (LOCA) are much less severe than the environmental conditions evaluated for qualification. The ambient temperature in the RHR pump rooms does not reach 115 degrees Fahrenheit until approximately 30 minutes after the LOCA if the RHR motor coolers are operating during the transient heat up phase. If the RHR motor coolers were not operating following the LOCA, the ambient temperature in the RHR pump rooms would not exceed 120 degrees Fahrenheit during the first 10 minutes of post-LOCA operation.

The RHR pump motors have been evaluated for long-term operation at an ambient temperature of 129 degrees Fahrenheit. In addition, the expected motor winding heat rise is only 39 degrees Fahrenheit after 30 minutes of operation. This is well below the 119 degrees Fahrenheit full winding temperature rise which occurs after the motor has been operating for approximately 90 minutes.

In conclusion, when the RHR pump motor coolers are not available, the RHR pump motor operating conditions for the first ten minutes following a LOCA are considerably less severe than the conditions which have been considered in the existing environmental qualification evaluation. This evaluation and its conclusions have been documented and are available at'.the.:, BFN'ite for review.

Commitment: FSAR Table 6.5-2 will be revised in the next annual update to reflect the correct long-and short-term pump combination requirements for core spray and RHR.

Resolution: The revision to FSAR Table 6.5-2 is in progress. As previously committed, the next annual FSAR update will be completed by 3uly 31, 1990.

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