Document: NRC Regulatory Guide
Document ID: ad61f8a3-1cce-4446-9542-dcdda55c1ec6
Document Type: regulatory_guide
Title: Comprehensive Vibration Assessment Program for Reactor Internals During Preoperational and Initial Startup Testing + HISTORY - HISTORY 07/2015 – DG-1323 , Proposed Revision 4 03/2013 – Periodic Review of Revision 3 – No Issues Identified 11/2006 – DG-1163 , Proposed Revision 3 (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1508/ML15083A390.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.20
CFR Part: 
CFR Title: 

Content:
and compressed by +/-10 percent and applied repeatedly to the structural dynamic model, with the worst case values retained and applied in the analysis. Several analysis increments are used, depending on the damping assumed. Previous acceptable analyses assuming 1 percent damping have used 2.5 percent frequency shifting increments in their analyses (i.e., loads are shifted by -10 percent, -7.5 percent, -5.0 percent, and so on up to +7.5 percent, +10 percent). Structural Damping The applicant or licensee should substantiate assumed structural damping. In some instances, the NRC’s damping guidance for very-low-frequency seismic analyses has been incorrectly applied as justification for using high damping factors for mid- to high-frequency analyses. Damping factors used in structural dynamic modeling need to be based on mid- to high-frequency measurements on structures representative of the reactor internals being modeled. Measurement techniques for damping are available in the standards promulgated by the American National Standards Institute (ANSI) and other organizations. The applicant or licensee should describe using measurement techniques for damping in the modeled environment (including air, steam, or water environments). Based on past experiences, specification of structural damping coefficients greater than 1 percent needs to be substantiated with measurements. DG-1323, Page 14 Some BWR licensees requesting EPU license amendments applied additional hydrodynamic damping to the dynamic response of perforated plates in steam dryer banks. Using similar hydrodynamic damping in future applications is acceptable where the estimated damping value is based on a sound technical foundation and is demonstrated to be conservative for the particular application. Frequency Response Functions The applicant or licensee should document the modeling approach as well as modeling details, including assumed boundary conditions and material properties, used to compute mode shapes