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:
sponse Functions The applicant or licensee should document the modeling approach as well as modeling details, including assumed boundary conditions and material properties, used to compute mode shapes and FRFs. The applicant or licensee should specify the uncertainties and bias errors associated with the approach and specific model, along with their bases. In many cases, bias errors in numerical models (such as for stress) are associated with insufficient mesh refinement of stress concentration regions and improper modeling of structural joints. These errors may be accounted for with stress concentration factors (SCFs). The uncertainties are often associated with differences between numerical models and as-manufactured structures, such as differences in material properties, connections (e.g., bolts, welds, and rivets), and geometries (e.g., plate and piping thicknesses). Bias and uncertainties associated with these differences may be estimated based on comparisons of simulations and measurements of structures similar in construction to the reactor internals being modeled. When benchmarking the structural dynamic modeling of components using dynamic testing, a sufficient number of drive and response points are applied to characterize all of the important modes of vibration and FRFs. The applicant or licensee should update the models to reflect reactor operating conditions, including material properties at operating temperatures, as well as water and steam fluid loading on reactor internals, including uncertainties in the natural frequencies and FRFs. Some structures might have variable or ill-defined boundary conditions during normal reactor operating conditions. Structural models need to address possible variations in the boundary conditions. For example, steam dryers rest on mounting pads attached to the RPV with variable amounts of contact area and supported load during normal operating conditions, such that there is no simple means for representing the boundary