ML19261B656

Forwards Final Rept Re Possible Unconservative Pressurizer Relief & Safety Line Blowdown Analysis. Concludes All Points in Lines Meet Allowable Stresses in Power Piping Code

ML19261B656
Person / Time
Site:	Sequoyah
Issue date:	02/22/1979
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 7902280353
Download: ML19261B656 (2)

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TENNESSEE VALLEY AUTHORITY CHATTANOOG A. TENNESSEE 37401 500C Chestnut Street Tower II FEB 2 2 1973 Mr. James P. O' Reil irector Office of Inspe on and Enforcement U.S. Nuclea - segulatory Commission Region - Suite 3100 101 ' riotta Street anta, Georgia 30303

Dear Mr. O'Reilly:

SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 - POSSIBLE UNCONSERVATIVE PRESSURIZER RLLIEF AND SAFETY LINE BLOWDOWN ANALYSIS - NCR CSQ 78 FINAL REPORT The subject deficiency was initially reported to NRC-OIE Inspector J. K. Rausch on May 5, 1978. Interim reports were submitted ou June 1, 1978, August 8, 1978, and December 12, 1978. Enclosed is our final report. d If you have any questions concerning this matter, please get in touch with M. R. Wisenburg at FIS 854-2581.

Very truly yours, J. E. Gilleland Assistant Manager of Power Enclosure cc: Mr. John G. Davis, Acting Director (Enclosure), V f Office of Inspection and Enforcement U.S. Nuclear Regulatory Counisalon Washington, DC 20555 7902280353 go An Equal Opportunity Employer s

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ENCLOSURE SEQUOYAll NUCLEAR PLANT UNITS 1 AND 2 POSSIBLE UNCONSERVATIVE PRESSURIZER RELIEF AND SAFETY LINE BLOWDOWN ANALYSIS - NCR CSQ 78-2 FINAL REPORT Description of Condition LDS Nuclear, Incorporated, a consulting engineering firm for TVA, per-formed a blowdown analysis of the pressurizer relief and safety lines using the computer program, RELAP4/ MOD 1. This program represented the state of the art at the time the analysis was performed in 1970, but because the program became unstable at lower temperatures, the analysis was accomplished using safety and relief valve water seal temperatures modeled at about 600 F (saturation temperature at the systeu design pressure), instead of the " worst case" temperature of 200 F.

A revised ve: sion of the original program has been developed which is capable of analysis at 200 F. Use of this revision (RELAP4/ MODS) on similar projects outside of TVA indicated that, because of the increased water slug effects at 200 F, a reanalysis may result in increased design loads and the need for additional supports.

Safety Implications liad the deficiency gone uncorrected, pressurizer saf t ty and relief lines may not have been ceaservatively designed. Therefore, it was assumed that the supports could not withstand their actual loads resulting in possible system failure. If failure occurred downstream of the system's isolation valves, the isolation valves would close the lines before any significant safety hazard developed. If the system failure occurred upstream of the isolation valves, a p.e-_urizer line blowdown would result creating a LOCA condition which the plant is designed to mitigate as described in Chapter 15 of the FSAR.

Corrective Action EDS reanalyzed the system using RELAP4/ MODS assuming a water temperature of 200 F and found that all points in the lines meet the allowable stresses in the USAS B-31.1 Power Piping Code.

Nozzle loads on the pressurizer and the pressurizer relief tank have been reviewed and found to be acceptable by Westinghouse.

Support designs were reviewed for new loads from the reanalysis and were found acceptable or were revised accordingly. The new supports have been designed and are in the process of being installed. Installation will be complete before fuel load in the associated unit.

Action to Prevent Recurrence All ut ra blowdown analyses will be performed using programs capable of modeling the valve water seal at defined temperatures.