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:
evealed failures of steam dryers and main steam system components (including relief valves) in BWR nuclear power plants following EPU implementation. These failures have demonstrated the importance of detailed analysis of potential adverse flow effects. Studies of those failures have determined that flow-excited acoustic resonances (where instabilities in the fluid flow excite acoustic modes) within the valve standpipes and branch lines in main steam lines (MSLs) can produce mid- to high-frequency pressure fluctuations in the standpipes of the MSL valves, causing their damage . These pressure fluctuations within the standpipes of the valves might also excite the acoustic modes of the steam columns in the MSLs, causing extremely high sound radiation and damaging the steam dryer, and possibly other reactor internals and steam system components. In those failures, the instabilities of the DG-1323, Page 4 separated flow (shear layer) over the standpipe openings “locked-in” to the acoustic resonance of the fluid column within the standpipe. “Lock-in” refers to feedback between the flow instability (i.e., shear layer oscillation) and the acoustic mode over a certain range of flow velocity, leading to strong amplification in the fluctuating pressures of the flow instability and acoustic mode. In addition, hydrodynamic loading acting directly on the steam dryer and other reactor internals and steam dryer components can produce FIV, causing excessive vibratory stresses. Variations in the reactor recirculation pump (RRP)1 speed can lead to changes in pump excitation frequencies and might affect its pulsation amplitude and transmitted mechanical vibration. As a result, nuclear power plant licensees have developed scale model testing (SMT) and structural and acoustic models to evaluate potential adverse effects. For SMRs, components such as CRDMs and steam generators (SGs) might be within or directly connected to the reactor pressure vessel (RPV). Consolidating reactor