ML20207C643

Responds to NRC Questions Re Use of Independent Support Motion (ISM) Method in Combinations W/Asme Code Case 411 Damping Values,Per 861215 Meeting.Results of Preliminary Study,Showing Impact to Piping Analyses,Provided

ML20207C643
Person / Time
Site:	Vogtle
Issue date:	12/22/1986
From:	Bailey J GEORGIA POWER CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
References
GN-1257, NUDOCS 8612300196
Download: ML20207C643 (2)

Text

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e Georgia Fbwer Company Fbst Offic^, Box 282 Waynesborr, Georgia 30800 Telephone 404 554-9961 404 724-8114 Southem Company Services, Inc.

Post Office Box 2625 Birmingham, Alabama 35202 b

Telephone 205 870-6011 VOgtie Project December 22, 1986 Director of Nuclear Reactor Regulation File: X4BP26 Attention: Mr. B. J. Youngblood Log: GN-1257 PWR Project Directorate #4 Division of PWR Licensing A U. S. Nuclear Regulatory Commission Washington, D.C. 20555 NRC DOCKET NUMBERS 50-424 AND 50-425 CONSTRUCTION PERMIT NUMBERS CPPR-108 AND CPPR-109 V0GTLE ELECTRIC GENERATING PIANT - UNITS 1 AND 2 USE OF ISM (MRS) COMBINED WITH CODE CASE N-411 DAMPING

Dear Mr. Denton:

At a meeting with the NRC on December 15, 1986 your staff asked questions concerning the use of the Independent Sapport Motion (ISM) method - otherwise known as the Multiple Response Spectrum (MRS) method - in combinations with A3ME Code Case N-411 damping values which have been used on the Vogtle Project. Georgia Power Company (GPC) presented the results of a preliminary study showing the impact to the piping analyses and supports if a different method of seismic analyses were used, i.e., use of the envelope spectra with N-411 or use of ISM (with absolute summation within groups) and Regulatory Guide 1.61 damping values. The preliminary results indicated that allowables had been exceeded for certain items.

It was concluded at the meeting that the study would be finalized and the results reported to the NRC for their review.

GPC has finalized this study and finds the following:

(1) Thirteen stress calculations within the Bechtel scope of piping syatems have used the ISM and N-411 combination for seismic analyses.

Approximately 600 pipe supports were included in these calculations.

Use of the different methods of seismic analysis resulted in changes in piping stresses, support .oads and other loads such as valve accelerations, equipment nozzle loads etc. However, these changes resulted in stresses and loads below design allowables and no hardware changes were required.

No additional high stress points have moved within SD of welded attachments, and the pipe break analysis has not been impacted.

l 8612300196 861222 PDR ADOCK 05000424 A PDR

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Director of Nuclear Reactor Regulation File: X4BP26 December 22, 1986 Ing: GN-1257 Page 2 (2) Three stress calculations within the Westinghouse scope of piping systems have used the ISM and N-411 combination for seismic analysis.- These calculation packages are for a non-safety related seismic Category II system designed to maintain structural integrity under SSE loads for hazards considerations.

Approximately 90 pipe supports are included in these calculations.

All three piping models have been reanalyzed using one of the two methods delineated above which are acceptable to NRC. The results of these reanalyses shows that both piping and support stresses are still within allowable stresses and no hardware changes were required.

The results of this study are documented and located in the project files.

The 16 identified calculations of record will not be altered and they will be revised only to reference the results of the study.

If the Unit 1 calculations are required to be revised in the future, for reasons other than clerical in nature, the seismic analysis will be performed using methods other than ISM in combination with Code Case N-411 unless this combination has been explicitly approved by the NRC.

Final Unit 2 calculations will also use seismic analyses methods other than ISM in combination with Code Case N-411 unless this combination has been explicitly approved by the NRC.

If your staff requires any additional information, please do not hesitate to contact me.

' Sincerely, Gs.

J. A. Bailey Project Licensing Manager JAB /sm xc: R. E. Conway NRC Regional Administrator R. A. Thomas NRC Resident Inspector J. E. Joiner, Esquire D. Feig B. W. Churchill, Esquire R. W. McManus M. A. Miller (2) L. T. Gucwa B. Jones, Esquire Vogtle Project File G. Bockhold, Jr.

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