Document: NUREG-0800
Document ID: 3d8f7691-e488-4083-af2f-eef689c0ec98
Document Type: srp
Title: ASME CODE CLASS 1, 2, AND 3 COMPONENTS AND COMPONENT SUPPORTS,
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0704/ML070430397.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.3
CFR Part: 
CFR Title: 

Content:
equipment deformations, the possible movements of the support base structures must be taken into account. B. Criteria for snubber functionality assurance should contain the following elements: 3.9.3-7 Revision 2 - March 2007 (i) Structural Analysis and Systems Evaluation. Systems and components which utilize snubbers as shock and vibration arresters should be analyzed to ascertain the interaction of such devices with the systems and components to which they are attached. Snubbers may be used as shock and vibration arresters and in some instances as dual purpose snubbers, and when so used fatigue strength should be considered. Important factors in the fatigue evaluation include: (1) unsupported system component movement or amplitude, (2) force imparted to snubber and corresponding reaction on system or component due to restricting motion (damped amplitude), (3) vibration frequency or number of load cycles, and (4) verification of system or component and snubber fatigue strength. Snubbers used as shock arresters need not undergo a fatigue evaluation if it can be demonstrated that: (a) the number of load cycles which the snubber will experience during normal plant operating conditions is small (<2500) or (b) motion during normal plant operating conditions does not exceed snubber dead band. Snubbers utilized in systems or components which may experience high thermal growth rates, either during normal operating conditions or as a result of anticipated transients, should be checked to ensure that such thermal growth rates do not exceed the snubber lock-up velocity. (ii) Characterization of Mechanical Properties. An important aspect of the structural analysis is realistic characterization of snubber mechanical properties (i.e., spring rates) in the analytical model. Since the "effective" stiffness of a snubber is generally greater than that for the snubber support assembly (i.e., the snubber plus clamp, transition tube extension, back-up support structure, etc.) the