Abstract
In order to clarify the effect of hydrodynamic fragmentation on molten fuel-coolant interactions, which is important in evaluating the sequence of core disruptive accidents in metallic fuel fast reactors, a series of basic experiments with a molten metallic fuel simulant (molten copper) and a sodium pool was carried out under an ambient Weber number condition (We) roughly equivalent to that in practical metallic fuel cores with high burnup. The value of the mass median diameter (D_m) of copper fragments normalized by the initial jet diameter (D_m/d_0) decreased with increasing the superheating of the molten copper jet, independently of the ambient Weber number under the condition of We<200. Under the condition of We>200, the effect of initial superheating temperature becomes negligible and the value of D_m/d_0 comes to depend on the ambient Weber number. This finding indicates that the transition of fragmentation mode from thermal to hydrodynamic occurs at the ambient Weber number of approximately 200.
