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:
distribution caused by all feasible combinations of pump operation patterns or natural circulation flow patterns needs to be evaluated. For example, for a particular BWR design, plant operation at 100 percent reactor flow with only 8 pumps running is likely to produce local flow velocities higher than those produced when 10 pumps are operating at the same reactor load. Consideration of such possibilities ensures that flow excitation mechanisms caused by the maximum possible flow velocity inside the reactor are taken into account in the vibration analysis. d. Grid size sensitivity tests need to be performed to demonstrate the independence of results from grid size. e. Steam needs to be modeled as a real gas. f. For unsteady flow simulations, acoustic/vibration coupling (if sufficiently significant to affect the flow behavior) needs to be included to simulate enhancement of flow instabilities. g. For unsteady flow simulations, the time step size needs to be demonstrated as not influencing the results (i.e., perform time step sensitivity tests). h. For unsteady simulations of high frequency flow oscillation, using large eddy simulation (LES) or direct numerical simulation (DNS) at high Reynolds number flow is acceptable. If used, LES, DNS, or other methods need to be demonstrated to be bounding for a representative test case. If applicable, compressibility effects need to be included to model any coupling of the flow and the acoustic waves in the fluid (for self-excitation and lock-in effects). i. When estimating upper bounds of dynamic forcing functions on reactor internals and other structural components, conservative simplifications and approximations need to be used if they are needed to complete the analysis. This includes, for example, estimating the correlation length and phase distributions of the fluid dynamic forces on structures exposed to fluid flow. j. Past review of EPU applications indicated that variability in reactor operating parameters can affect