Development of Passive Shutdown System for SFR

A sodium-cooled fast reactor (SFR) self-actuated shutdown system (SASS) is a passive safety feature by which control rods are inserted by gravity force and the rods would be detached by a rise in coolant temperature under anticipated transient without scram (ATWS) conditions. Various out-of-pile tests have already been carried out to investigate the basic characteristics of SASS, and a demonstration test of the holding stability under reactor operation conditions has been performed, where a function test of the driving system to reconnect and pull out the control rod has been done in the experimental reactor JOYO. Element irradiation tests have also been conducted to confirm that there is no impact from irradiation. The effectiveness of SASS for the reference core design of the Japan SFR (JSFR) has been evaluated through all ATWS types. As a result, it is ensured that JSFR will have a reliable passive shutdown system.