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:
e drive and CRDS component natural frequencies because excessive vibration could lead to interference with the operation of the control rods. If potential self-excitation or lock-in is identified, the applicant/licensee should establish specific mitigation procedures where the lock-in leads to vibration or stress that exceeds allowable limits. For example, the following forcing functions need to be addressed for lock-in susceptibility: a. Flow (or shear layer) instabilities over openings in the MSLs, such as control and safety valve standpipes and dead-end flanges, can lead to strong narrow-band excitation because of lock-in with acoustic or structural resonances. For example, acoustic resonances in standpipes can be excited by various shear layer oscillation modes (also known as hydrodynamic modes). Acoustic resonances excited by the first shear layer mode (the lowest frequency of shear layer oscillation) might be significant and, therefore, need to be mitigated by suitable design modifications (e.g., acoustic side-branches attached to standpipes) or operating condition changes. Information on acoustic resonances can be found in ASME PVP 2007-26658, “Identification of Quad Cities Main Steam Line Acoustic Sources and Vibration Reduction” (Ref. 7). On the other hand, the excitation by the second (and higher) shear layer mode generally produces less significant resonances and, therefore, excitation by the higher shear layer modes might be acceptable if the resulting vibration and alternating stresses in relevant components are demonstrated to meet the acceptable limits. Acceptable assessment of acoustic resonance of standpipes addresses the effect of the following parameters: DG-1323, Page 17 (1) Strouhal number analysis to evaluate critical flow rates (including uncertainties in the Strouhal number), (2) effects of the ratio between the standpipe and main pipe diameters, (3) effects of edge radii at the inlet of the standpipes, (4) effects of upstream elbows, (5)