Design and Development of Fast Breeder Reactor Passive Reactivity Control Systems: LEM and LIM

To enhance the inherent safety of the fast breeder reactor (FBR), unique attempts are being made in reactivity control systems design to achieve maintenance-free and reliable performance at the Central Research Institute of the Electric Power Industry. The design involves the lithium expansion module (LEM) for inherent reactivity feedback and the lithium injection module (LIM) for inherent ultimate shutdown. Reactor physics calculation revealed the reactivity worth of LEM and LIM in a 60-MW(electric), metal-fueled FBR and a 1000-MW(electric) mixed-oxide-fueled FBR. The system dynamics analyses revealed that LEM and LIM are effective to avoid sodium boiling in unprotected transient overpower and unprotected loss-of-flow transients. Reliability, maintainability, and real-time monitoring for LEM and LIM are also discussed.