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:
ith the traditional semi-empirical method that has been successfully employed for many years. The first method is analogous to the traditional method. The finite element analysis results from a global model of the structure, subjected to the applied dynamic loading, are used to calculate a nominal average stress plus linear bending stress at the location of the double fillet weld. The fillet weld is a local detail and is not included in the global model. Solution convergence with mesh refinement needs to be established before proceeding to the next step. The worst case nominal stress distribution at the double fillet weld location is multiplied by a factor of 4, to obtain the peak stress estimate for use in the fatigue evaluation. The most conservative approach is to assume that the calculated peak stress occurs in both the positive and negative directions, producing a peak stress range equal to 2 times the calculated peak stress. The alternating peak stress, which equals half of the peak stress range, is then equal to the calculated peak stress. At the initial design stage, a safety factor (e.g., 2) may be applied to account for uncertainty, or another factor justified. After the calculated peak stress is adjusted based on measurements taken during power ascension testing, the safety factor is not necessary. The adjusted peak stress needs to be less than the endurance limit. The second method follows the first method, through post processing of the results of the global model analysis, as described above. This establishes the loading and location for a detailed submodel analysis. In the detailed submodel analysis, idealized fillet welds are explicitly modeled using an array of solid elements. The linearized stress distribution through the throat of the fillet weld is calculated from the solid element stress output. The adequacy of the solid element mesh in the submodel needs to be verified by a stress convergence study. The converged, linearized stress prediction