Passive shutdown device for gas cooled fast reactor: Lithium injection module

In this paper a passive reactivity control system for a Gas Cooled Fast Reactor is proposed. The Generation IV GCFR features a core with a relatively high power density, and control of transients and adequate shutdown under accidental situations must be assured for safe operation. Using a passive shutdown device rules out the possibility of unprotected transients. The proposed devices work by the passive introduction of 6Li into the core (Lithium Injection Module). Control is by the outlet temperature of the coolant gas in the fuel assemblies, employing a freeze seal. The proposed devices can be integrated into the regular control assemblies. A total of four LIMs is proposed in the core. Thermohydraulic calculations were done using the CATHARE code for a 600 MWth GCFR, for 2 types of transients: a loss of flow, and a control rod withdrawal. The calculations show that activation of one LIM is sufficient to keep the reactor power bounded, while activation of all LIMs in the core will shut down the reactor. The passive LIM devices are able to exclude unprotected transients in the GCFR core. (authors)