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:
Feedback and Lock-In Mechanisms The applicant or licensee should evaluate forcing functions that might be amplified by lock-in with an acoustic or structural resonance (referred to as self-excitation mechanisms). A lock-in of a forcing function with a resonance strengthens the resonance amplitude. The resulting amplitudes of the forcing function and resonance response can therefore be significantly higher than the amplitudes associated with non-lock-in conditions. The applicant or licensee should address all potential flow-excited acoustic or structural resonances that lead to feedback and loading amplification. Tables may be used to specify expected flow rates and resonance frequencies, along with the possible ranges of lock-in and potential loading amplifications. The applicant or licensee should define the uncertainties in any of the lock-in parameters (such as the characteristic Strouhal numbers of the flow-excitation sources). The applicant/licensee should compare flow instability frequencies to those of acoustic and structural modes in the reactor dome, MSLs, any connected valves, and reactor internals, as applicable. The amplitude of any identified self-excitation or lock-in should not be analyzed by simply applying linear extrapolation techniques. Finite element simulations or measurements may be used to determine the resonance frequencies. The applicant or licensee should evaluate reactor internals that could be excited by fluid flow which contracts and accelerates between the gaps and annuli among reactor internals. For example, for the CRDS, flow excitation of the control rods, CRDMs, tie rods and plates, upper flange webs, and around the power cables should be assessed. In addition, the applicant or licensee should evaluate the potential coincidence of the 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