Scram reliability under seismic conditions at the Experimental Breeder Reactor II

A level 1 probabilistic risk assessment of the Experimental Breeder Reactor 11 has recently been completed. Seismic events are among the external initiating events included in the assessment. The analysis indicated that the reactor shutdown system had a high reliability of operation in response to internally initiated events. One of the major tasks within the seismic assessment concentrated on the ability to shut down the reactor under seismic conditions. A comprehensive analysis of the shutdown system, including the development of a finite element model of the reactor control rod drive system, has been used to estimate the system response when subjected to input seismic accelerations. The results indicate the control rod driven system has a high seismic capacity and that the overall reactor shutdown system is capable of maintaining its high reliability under seismic conditions. The estimated seismic fragility for the overall reactor shutdown system is dominated by the primary tank failure.