ML19256F641

Interim Deficiency Rept Re Seismic Response Spectrum Curves in Pipe Stress Analyses.Three Inconsistencies Discovered in Amplified Response Spectrum Curves Used as Input Data to Pipe Stress Analyses.Analyses Rerun Using Proper Input

ML19256F641
Person / Time
Site:	North Anna
Issue date:	12/04/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
REF-PT21-79-172-001 934A, NUDOCS 7912190663
Download: ML19256F641 (2)

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• 0 Ve co e VIRGINt A ELECTRIC AND POWER COMP ANY, RICHMONO, VIRGINI A 23261

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• 35 December 4,1979 Mr. James P. O'Reilly, Director Serial No. 934A Office of Inspection & Enforcement PSE&C/CGC:mac:wqng U. S. Nuclear Regulatory Commission .

Region II Docket No. 50-339 101 Marietta Street, Suite 3100 At1anta, Georgia 30303

Dear Mr. O'Reilly:

Pursuant to the provisions of 10CFR50.55(e) and 10CFR21 you were notified on November 5, 1979 and by letter (Serial No. 934) dated November 9, 1979 concerning seismic response spectrum curves in some pipe stress analyses. In our November 9 letter, we stated that this problem applies to 44 MSK's on Unit 1, 18 of which are applicable to Unit 2 as well. We have since taken one (1) of these 18 and created a new separate MSK for Unit 2; therefore, we now have 44 MSK's for Unit 1, 17 of which apply to Unit 2, plus one (1) MSK unique to Unit 2.

A description of the problem follows:

We have discovered inconsistencies in the way in which certain of the seismic amplified response spectrum (ARS) curves were used as input data to pipe stress analyses for North Anna Units 1 and 2. An investigation has shown three types of inconsistencies in the ARS data were present. The first inconsistency was that certain curves had two or more values of acceleration for the same period (i.e. multiple periods). The second was that the peak-spreading of some curves was not exactly +_15 percent of the peak's period as described in FSAR Section 3.7.3. The third discrepancy was that a few of the ARS curves were outdated.

It has been determined, by a complete review of the ARS input to pipe stress calculations, that there are no inco.isistencies other than those described above. These discrepancies affect only the dynamic analysis of piping systems; the static analysis involving seismic building movements is not affected.

For North Anna 2, only the second and third types of inconsistencies exist - no multiple periods exist. The use of seismic input with these inconsistencies could potentially result in nonconservative pipe stresses, pipe g9 support loads, and equipment loads in safety-related systems located in the auxiliary building, the service N-

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e 2-water pump house, and the main steam valve house. Systems affected are service water, quench spray, safety injection, component cooling water, and containment hogger. Only portiens of these systems are affected. No portions of these systems within the containment or the reactor coolant system pressure boundary are affected.

Corrective action is in progress for this problem. The pipe stress analyses for all 18 MSK's have been rerun using the proper ARS input; these reanalyses identified two overstressed pipes each requiring the addition of one support to bring the pipe stress within the allowable. Also identified by the pipe stress reanalysis is the need for one support to restrict the seismic displacement of the rubber expansion joints for the service water to the component cooling water heat exchanger. Still in progress is the analysis of the eff ect on existing pipe supports, equipment, and equipment supports of new loads derived from the pipe stress reanalyses. Modifications will be made as required.

We consider this to be an interim report; any information not available at this time will be submitted in a final report. Should you require further information, please contact this office.

Very t uly yours, Y 7e c <

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.B/own#,

Sant Senior Vice rgfdent-PowerStation Engineering and Construction cc: Mr. Victor Stello, Director Office of Inspection & Enforcement Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation 1626 427