Experimental research on fragmentation of continuous molten copper droplets penetrating into sodium pool

In order to characterize the relationship between hydrodynamic and thermal fragmentation of molten metallic fuels with the interaction of the coolant of sodium in the wide range of thermal and hydrodynamic conditions, the present paper focuses on the fragmentation characteristics of continuous molten copper droplets with a total mass from 20 to 50g penetrating into a sodium pool in a wide range of instantaneous contact interface temperature (T_i) and ambient Weber number (We_a), compared with the previous data of 1-5g single molten copper droplet and 20-300g copper jets. Fine fragmentations of the single molten copper droplets with a high We_a were clearly observed even under a supercooled condition that is well below the copper melting point of 1083℃. The fragmentation of the continuous molten copper droplets is insensitive to the change of the hydrodynamic under the relatively higher thermal conditions. The hydrodynamic effect on fragmentation became dominant over the thermal effect under a relatively low superheating condition. The comparison shows that the continuous droplets are more likely to fragment finer than the single droplet under the similar conditions. The present mass median diameter (D_m) or dimensionless mass median diameter (D_m/D₀) of continuous copper droplets shows a distribution with smaller values than those of single copper droplet, and larger values than those of copper jets under similar thermal and hydrodynamic conditions. These results are promising to assure the termination of accidents in CDAs and useful to the core design with enhanced safety in FBRs. (author)