Development of a self actuated shutdown system for large scale JSFR

A self-actuated shutdown system (SASS) has been developed for the Japan Sodium-cooled Fast Reactor (JSFR) to enhance safety against anticipated transients without scram (ATWS). The SASS is a passive reactor shutdown device, which can detach a control rod in response to an abnormal increase of coolant temperature using the nature of ferromagnets that lose their magnetic property around their Curie points. In this study, functional and structural requirements for the SASS to suit the current JSFR design were specified and the SASS, which could fulfill the requirements, was successfully designed. Moreover, a validation analysis of the SASS on its effectiveness against ATWS was carried out. The result shows that the SASS could apply to all types of ATWS, the transient over power type, the loss of flow type, and the loss of heat sink type. Thus, the feasibility of the SASS, which is important to enhance safety of the JSFR, was confirmed. (author)