Document: NRC Regulatory Guide
Document ID: b6726dc6-2968-4ca9-a925-c831eaaecc69
Document Type: regulatory_guide
Title: 03/2007
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0702/ML070260029.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.61
CFR Part: 
CFR Title: 

Content:
requesting document displays a currently valid OMB control number. B. DISCUSSION Background Damping is a measure of the energy dissipation of a material or structural system as it responds to dynamic excitation. It is a term used to assist in mathematically modeling and solving dynamic equations of motion for a vibratory system in which energy is dissipated. When performing an elastic dynamic seismic analysis, one can account for the energy dissipated by specifying the amount of viscous damping (i.e., damping force proportional to the velocity) in the analytical model. Current NRC guidance on damping values to be used in the elastic design of nuclear power plants is presented in this regulatory guide, which was first issued in October 1973 [Ref. 2]. Like the original version of this guide, this revision specifies equivalent viscous modal damping values as a percentage of critical damping for Seismic Category I SSCs. However, the staff based the original damping values on limited data, expert opinion, and other information available in 1973. Since that time, the NRC and industry have been involved in various studies, research work, and testing to predict and estimate damping values of SSCs. In view of the available data, the damping values provided in the original version of Regulatory Guide 1.61 may not reflect realistic damping values for SSCs. Also, it is recognized that additional guidance is needed to address issues, such as correlation between damping and structures stress level, and damping values for materials not included in the original version of Regulatory Guide 1.61 (e.g., electrical distribution systems and reinforced masonry structures). Over the past three decades, the nuclear industry has proposed damping values and discussed these values during various meetings and reviews of licensing issues. Nuclear industry groups and licensees have suggested that the NRC ought to accept more realistic damping values for seismic design and analysis of SSCs, in