Resolution of Generic Safety Issues: Item A-13: Snubber Operability Assurance (Rev. 2) ( NUREG-0933, Main Report with Supplements 1–34 )
Historical BackgroundIn May 1978, the ACRS and the staff expressed concern over the substantial number of LERs related to the malfunction of snubbers, the most frequent of which were: (1) seal leakage in hydraulic snubbers; and (2) high rejection rate during functional testing of snubbers. In reviewing these LERs, the staff noted differences in the numbers of snubbers utilized in systems of similar configurations and questioned the methodology used for determining the need for snubbers in any given system. As a result of these concerns and the desire to provide a significant increase in assurance of the health and safety of the public, snubber operability assurance was given a priority Category A designation and included in NUREG-0371. 2
Snubbers are utilized primarily as seismic and pipe whip restraints at nuclear power plants. Their safety function is to operate as rigid supports for restraining the motion of attached systems or components under rapidly applied load conditions such as earthquakes, pipe breaks, and severe hydraulic transients.
The solutions proposed in NUREG-03712 were as follows: (1) evaluation of industry practice associated with snubber qualification testing, design and analysis procedures, selection and specification criteria, and pre-service and in-service inspection programs; and (2) development of TS, SRP11 revisions, and Regulatory Guides to assure a high level of snubber operability.
In 1980, the staff addressed the operation of snubbers with revisions to STS 3/4.7.9; SRP11 Section 3.9.3 was later revised in 1981. A draft regulatory guide (Task SC-708-4)12 on the qualification and acceptance tests for snubbers used in systems important to safety was issued by the staff, but was later withdrawn when it was determined that there were no plans for its use in the licensing process.9 Thus, with the SRP revision, this issue was RESOLVED and requirements were issued.