ML20138H970

Application for Amends to Licenses NPF-4 & NPF-7,revising FSAR Damping Values Used for Seismic Analysis of Piping to Be Consistent W/Asme Code Case N-411 Damping Values Recommended in NUREG-1061.Fee Paid

ML20138H970
Person / Time
Site:	North Anna
Issue date:	10/21/1985
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Butcher E, Harold Denton Office of Nuclear Reactor Regulation
References
RTR-NUREG-1061 85-706, NUDOCS 8510290197
Download: ML20138H970 (2)

Text

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VIMOINIA l$LECTHIC AND l'OWHH COMi%NY Ricunown,VinoixiA ununt W L. STEWART sNE='.. "o'[U".. October 21, 1985 Mr. Harold R. Denton, Director Serial No.85-706 Office of Nuclear Reactor Regulation E&C/KKD/JDH:acm Attn: Mr. Edward J. Butcher, Acting Chief Docket Nos. 50-338 Operating Reactors Branch No. 3 50-339 Division of Licensing License Nos. NPF-4 U. S. Nuclear Regulatory Commission NPF-7 Washington, D. C. 20555 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPAhT NORTH ANNA POWER STATION UNIT NOS. 1 AND 2 PROPOSED CHANGES TO DAMPING VALUES FOR SEISMIC ANALYSIS OF PIPING The present North Anna 1 and 2 design criteria for seismic Category I piping is stated in the UFSAR, Section 3.7.3.1.1. The damping factors used are 0.5 percent for the operating-basis earthquake (OBE) and 1 percent for the design-basis earthquake (DBE). Studies conducted by the Pressure Vessel Research Committee (PVRC) as documented in NUREG 1061, " Report of the U. S.

NRC Piping Review Committee" have shown that use of such low damping values for seismic analysis of piping is unduly conservative. We therefore reque.st permission to use the damping values given in the ASME Code Case N-411 as reccmmended in NUREC 1061. These values specifically are: five percent below frequency of 10 Hz; linear reduction from five percent to two percent between 10 Hz and 20 Hz; and two percent above 20 Hz. These damping values would apply for both OBE and DBE.

The use of higher damping values is consistent with industry efforts to reduce the number of seismic restraints, particularly snubbers. The hardware reliability, inservice inspection and maintenance difficultien of snubbers inherently detract from the safety of Category I piping, as reported in NUREG/CR-3718 " Reliability Analysis of Stiff vs. Flexible Piping -- Status Report."

These damping values would be used in the following situations and with the following additional considerations:

a. For seismic analyses in cases where new piping is added, existing systems are modified, existing systems are re-evaluated for new requirements and where existing numbers of snubbers are to be reduced.

b. For seismic analysis using response spectrun. ecchods and not for seismic analysis using time-history analysis methods.

8510290197 851021 PDR ADOCK 05000338 P

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, 'o VanOzxtA EtzcTarc Ann Powan COMPANY TO Mr. Harold R. Denton

c. When these damping values are used, the +/-15% peak broadening criteria of Regulatory Guide 1.122, " Development of Floor Design Response Spectra for Seismic Design of Floor-Supported Equipment or Components," will be used.

d. When these damping values are used, they will be used in a given analysis in their entirety,

e. When these damping values are used together with changes in the support arrangement that increases the flexibility of piping systems, the predicted maximum displacements will be reviewed in accordance with applicable procedures to ensure that such displacements do not cause adverse interaction with adjacent structures, components or equipments.

Pursuant to 10CFR170, an application fee of $150 is attached.

Very truly yours,

.\(D (3g W. L. Stewart

Attachment:

Application Fee cc: Dr. J. Nelson Grace Regional Administrator Region II Mr. M. W. Branch NRC Resident Inspector Vorth Anna Power Station