Document: NUREG-0800
Document ID: fb538e14-08a0-4d3f-a974-8170cbfe0b5b
Document Type: srp
Title: ASME CODE CLASS 1, 2, AND 3 COMPONENTS,
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340603.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.3
CFR Part: 
CFR Title: 

Content:
arrestor or dual purpose snubbers, fatigue strength must be considered. Important factors in the fatigue evaluation include: (i) unsupported system component movement or amplitude, (ii) force imparted to snubber and corresponding reaction on system or component due to restricting motion (damped amplitude), (iii) vibration frequency or number of load cycles, and (iv) verification of system or component and snubber fatigue strength. Snubbers used as shock arrestors do not require fatigue evaluation if it can be demonstrated that (i) the number of load cycles which the snubber will experience during normal plant operating conditions is small (<2500) or (ii) 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 condi- tions or as a result of anticipated transients should be checked to assure that such thermal growth rates do not exceed the snubber lock-up velocity. 3.9.3-5 Rev. 1 - July 1981 (2) Characterization of Mechanical Properties. A most 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 snubber response characteristics may be "washed out" by the added flexibility in the support structure. The combined effective stiffness of the snubber and support assembly must therefore be considered in evaluating the structural response of the system or component. Snubber spring rate should be determined independent of clearance/ lost motion, activation level, or release rate. The stiffness should be based on structural and hydraulic compliance only, and should consider the effects of temperature. The snubber end fitting clearance