The Department of Energy uses the Advanced Test Reactor (ATR) at Idaho National Laboratory to test nuclear fuel systems and materials. The light-water moderated and cooled reactor has a four-leaf clover design that allows for a variety of testing options. The structures, systems, and components (SSCs) essential to plant safety include coolant system piping, pumps and heat exchangers, diesel generators, switchgear, transformers, control panels, batteries, battery chargers, and instrumentation. The majority of the SSCs are contained in the TRA-670 building, which consists of a reinforced concrete substructure and steel superstructure. In response to evolving seismic criteria and knowledge, Battelle Energy Alliance decided to update the 1991 seismic probabilistic risk assessment (SPRA) of the ATR and SGH developed seismic fragilities in support of the new SPRA.