Experimental Research on Energy Release and Fragments Characteristics Under Molten Materials Discharged Into Liquid Sodium

Abstract

Hypothetical Core Disruptive Accidents (HCDA) are dominantly concerned during safety assessment and evaluation in Sodium-cooled Fast Reactor (SFR). With molten core materials discharged into liquid sodium, positive reactivity is potentially introduced due to sodium boiling and molten core compaction, which can cause terrible recriticality. The possibility of recriticality and efficient cooling on the relocated debris bed are significantly affected by the fragmentation behavior of molten core in liquid sodium. With few available mechanism models and benchmarks, many investigations have been conducted on the fragmentation characteristics during molten fuel-coolant interaction (MFCI). In the present study, molten copper is used for molten simulant to be discharged into the liquid sodium pool through guiding tube based on a multifunctional experimental facility (COSA). The simulants are heated by electromagnetic induction system in customized ceramic crucible and the molten materials are controlled by magnetic lifting system to be drained through the guiding tube into the bottom liquid sodium pool. Temperature variation and pressure change in the liquid sodium pool are acquired against the energy release during MFCI. Furthermore, the fragments cleaned by water medium are measured and recorded for distribution and morphology analysis. Significant pressure pulses and temperature gradient almost not occur during MFCI and the molten copper is finely fragmented possibly due to hydrodynamic and thermodynamic effects. And the experimental results are helpful to confirm the prediction of fragmentation mechanism and to validate physical model, which can be applied to the development and validation of analysis code.