Zion SQUG pilot walkdown and resolution of outliers

Abstract

A walkdown of Zion Unit 2 was performed in May 1987 to verify the seismic adequacy of mechanical and electrical equipment required for hot safe shutdown. This was the first pilot walkdown performed under the SQUG guidelines. Draft Generic Implementation Procedures developed by SQUG were used by the three Seismic Review Teams to walkdown 159 pieces of equipment. Based on the walkdown, 118 pieces of equipment were found to be adequate and the remaining 41 pieces were classified as outliers. Seven of these 41 outliers were further verified by subsequent walkdown and 17 were verified by additional calculations. Anchorage repairs/improvements and minor field adjustments due to seismic interaction concerns resolved the remaining 17 cases. A trend analysis of the outliers was also performed to see if other safety-related equipment, outside the scope of SQUG, should be addressed for any shortcomings. Two trends were identified, one for the anchorage of shop fabricated instrument racks, and another for bracing of HVAC duct system supplying intake air to the diesel generators. Appropriate repairs were issued for all safety-related items affected by these trends.