Evaluating seismic functionality of relays in operating nuclear plants

This paper presents the current status and principal activities of a project to develop the methodology and procedure to evaluate seismic functionality of relays in operating nuclear power plants. The need for the relay evaluation procedure arouse in response to concern regarding relay seismic fragility identified in NRC Unresolved Safety Issue (USI) A-46, Seismic Qualification of Equipment in Operating Nuclear Power Plants. The authors in support of the Seismic Qualification Utility Group (SQUG), has undertaken a program to demonstrate the seismic adequacy of essential equipment by the use of actual experience with such equipment in plants which have undergone significant earthquakes and by the use of available test data for similar equipment. An important part of this program is the development of the methodology and test data for verifying the functionality of electrical relays used in essential circuits needed for plant shutdown during a seismic event