Analysis of core meltdown energetics in KALIMER

Core disruptive accidents have been investigated at Korea Atomic Energy Research Institute(KAERI) as part of the work to demonstrate the inherent and ultimate safety of conceptual design of the Korea Advanced Liquid Metal Reactor(KALIMER), a 150 Mwe pool-type sodium cooled prototype fast reactor that uses U-Pu-Zr metallic fuel. In this study, a simple method was first developed using a modified Bethe-Tait method to simulate kinetics and hydraulic behavior of a homogeneous spherical core over the period of the super-prompt critical power excursion induced by the ramp reactivity insertion due to the fuel compaction. A set of test calculations was made and compared fairly well with the results of more detailed analysis by Hicks and Menzies for core meltdown energetics of the oxide fuelled fast reactor. Calculations of the energy release during excursions in the sodium-voided core of the KALIMER were subsequently performed using the simple method for various reactivity insertion rates up to 200 $/s. Given the value of Doppler constants of the KALIMER(in the range of -0.001 to -0.02 at around the melting temperature of the fuel), power excursions were terminated without an energetic disassembly even for the extremely large reactivity insertion rates of 100 $/s, which are considered the upper limit of ramp rates due to fuel compaction; either the core does not reach the boiling temperature of the fuel, or the central core in small scale dispersal at low pressure