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:
ue is not allowed to result in a reduction or distortion of stress in the plate at the connection. The next step is developing a suitable finite element mesh, consistent with the loading, the expected structural response, and the intended use of the stress analysis output. The finite element mesh for the dynamic model needs to be sufficiently refined to (1) capture the spatial variation of the applied dynamic pressure loading; and (2) accurately respond up to the highest frequency contained in the dynamic pressure loading. To ensure item (2), a mesh sensitivity study needs to be conducted. For local areas of the stress model, where stress output for fatigue analysis will be extracted, it is necessary to check stress convergence by systematically reducing the local element size. Before applying appropriate SCFs to the model stress output, it needs to be established that the desired stress output has converged, or that a reasonably accurate projection of the converged stress can be made from the results of the successive mesh refinement analyses. DG-1323, Page 25 The final step in the model development is specification of the dynamic analysis parameters. This will depend on the selected method of solution; i.e., time domain or frequency domain. If time domain is selected, then the solution time increment should be no larger than 0.125 times the shortest period of interest. For example, if 250 Hz is the highest frequency of interest, then the solution time increment should be no larger than 0.125/250 = 0.0005. Rayleigh damping of 1 percent is acceptable for BWR steam dryers. To ensure that the solution is not over-damped in the frequency range of interest, 1 percent should be specified at 0 Hz and at the highest frequency of interest. This will be conservative at intermediate frequencies. Alternate Rayleigh damping anchor frequencies need to be quantitatively justified. For components other than BWR steam dryers, higher values of damping may be appropriate if