DEVELOPMENT OF A PASSIVE REACTOR SHUTDOWN DEVICE TO PREVENT CORE DISRUPTIVE ACCIDENTS IN FAST REACTORS:

(1) SAFETY ANALYSIS OF DEVICE-LOADED CORES WITH DIFFERENT FUEL MATERIALS

Abstract

A new subassembly-type passive reactor shutdown device has been proposed to expand the versatility and robustness of core disruptive accident prevention measures for sodium-cooled fast reactors (SFRs). This device can passively provide a large negative reactivity to the core by rapidly transferring the device fuel, which liquefies as the core temperature rises during an accident, to the lower plenum region of the device pins using only simple physical phenomena such as gravity falls. The fuel used in this device is assumed to be a metal alloy or chloride with the characteristics of fast reactor fuel and a relatively low melting point. In this study, the transient response analysis of the initiating phase during a typical unprotected loss of flow (ULOF) event was performed for a device loaded core of 750 MWe-class MOX fuel SFR, and the effect of different device fuel materials on the event termination was investigated. The results indicate that, no matter what device fuel material is used, it is expected to be possible to terminate the ULOF event without coolant sodium boiling in the core during the initiating phase of the event by replacing about 30 of the 286 fuel subassemblies in the core with device fuel subassemblies.