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:
om prototype plants to demonstrate that the results are bounding. BUFs represent the ratios between the dynamic loadings at a power level to that measured at a lower power level. In addition, BUFs are generally location- and frequency-dependent and their minimum value at any frequency cannot be lower than the square of the ratio between the characteristic flow velocities of both power levels. j. Plant-specific data are needed to demonstrate the acceptability of SMT test data and confirm the vibration analysis results. CFD Modeling If CFD models are used to develop unsteady forcing functions or compute the distribution of flow velocity to develop the forcing functions, applicable items from the following list need to be addressed: a. The dynamic fluid forces acting on reactor internals and other SSCs exposed to fluid flow are often estimated from the local flow velocity and density, which are computed by DG-1323, Page 19 means of CFD codes. All computational codes used in the vibration analysis to determine local flow velocities need to be validated on systems which are similar to the plant components in both geometrical complexity and flow regime. b. When constructing fluid domain models to be used in CFD and thermal-hydraulic codes, an accurate representation of the fluid domain geometry details within the reactor vessel is needed, including proper definitions and representations of the smallest flow areas, and additional features inside an SMR reactor vessel (such as internal CRDM mechanisms). c. The flow distribution inside the RPV might not be uniformly distributed–for example, if the design includes RRPs or multiple piping inlets in a natural circulation mode. When performing the vibration analysis of the reactor internals, the worst scenario of reactor flow 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