ML20012C625

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Forwards Rev 2 to TVA Calculation SQN-SQS2-0097, Probabilistic Analysis Showing Effects of Deleting RHR Autoclosure Interlock.
ML20012C625
Person / Time
Site: Sequoyah  Tennessee Valley Authority icon.png
Issue date: 03/15/1990
From: Wallace E
TENNESSEE VALLEY AUTHORITY
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20012C626 List:
References
NUDOCS 9003220297
Download: ML20012C625 (3)


Text

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TENNESSEE VALLEY. AUTHORITY CH ATTANOOGA, TENNESSEE 37401 SN 1578 Lookout Place 1AAR 151990 i

A U.S. Nuclear. Regulatory Commission

[( ATTN: Document Control Desk IiL kutshington, D.C. 20555 l

Gentlemen: '

In the Matter of ) Docket Nos. 50-327 ,

Tennessce Valley Authority-

) 50-328 SEQU0iAH NUCLEAR PLANT (SQN) - TECHNICAL SPECIFICATION (TS) CHANCE 89-18, ADDITIONAL INFORMATION

Reference:

TVA letter to NRC dated December 8, 1989, "Sequoyah Nuclear Plaat (SQW) - Technical 5;,ecification (TS) Change 89-18" This letter provides a revision to TVA Calculation SQN-SQS2-0097 and provides i the Westinghouse Electric. Corporation's report docun.cnting-the qualitative evaluation of the SQii design for the residual heat removal (RHR) system autoclosure interlock deletion.

Enclosure 1 of this letter contains Revision'2 of TVA Calculation SQN-SQS2-0097. Revistoa I was provided as an attachment to Enclosure 2 in the referenced letter. The caleviation revision was discussed with Harry Balukjian and Jack Dononew of ycur staff on February 5,1990. ,

During a review of the calculation, TVA identifled language that could lead to an incorrect interpretaiton. The reference made to RHR suction valves not opening against full reactor coolant system (RCS) pressure was made as a partial explanation of why premature opening of the valves was not addressed in the Westinghouse Owner's Group analysis. This r-forence was to Salem Nuclear Plant; SQN's present design does not dtplicate Salem. TVA has increased the RHR suction valves' motor sizes and disconnected the torque

, switches. SQN's valves, therefore, may be cepable of opening against full RCS pressure. However, SQN's design contains an open ph.niss'se interlock to reduce the likelihood of inadvertent opening. Additionaily, the electrical power to these valves is procedurally locbd out as an extra preventative W; measure. Thus, the conclusions of the cal;ulation remain unchanged.

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d0 An Equal Opportunity Employer V

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j U.S. Nuclear Regulatory Commission MAR 151990

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4- Enclosure 2 contains the Westinghouse report that documents a comparative evaluation between Salem and SQN with regard to the deletion of the autoclosure interlock. Based on SQN's proposed alarm configuration, estimated failure probabilities for interfacing system loss of coolant accident potential, RHR system availability, and low-temperature overpressurization were determined. In each case, the failure probability for SQN with the autoclosure interlock removed and the main control room alarm installed is y less than the failure probability with the autoclosure interlock remaining.

!- The results and conclusions for Salem in Westinghouse NCAP-11736-A, " Residual l' Heat Removal System Autoclosure Interlock Removal Report for the Westinghouse Owners Group," are not invalidated by the proposed design for SQN.

No commitments are contained in this submittal. Please direct questions concerning this issue to Kathy S. Whitaker 6t (615) 843-7748.

Very truly yours, TENNESSLE VALLEY AUTHORITY Aw E. G. Wallace, Manager Nuclear Licensing and Regulatory Affairs Enclosures cc (Enclosures):

Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White flint, North 11555 Rock /ille Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NH, Suite 2 LOO Atlanta, Georgia 30323 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 o .,

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ENCLOSURE 1 REVISION 2 0F TVA CALCULATION SQN-SQS2-0097 .

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