Transformation and fragmentation behavior of molten aluminum drop in sodium pool

In order to clarify the fragmentation mechanism of a metallic alloy (U-Pu-Zr) fuel on liquid phase formed by metallurgical reactions (liquefaction temperature = 650 degree C), which is important in evaluating the sequence of core disruptive accidents for metallic fuel fast reactors, a series of experiments was carried out using molten aluminum (m.p. 660 degree C) and sodium under the condition that the boiling of sodium does not occur. The thermal fragmentation of a molten aluminum drop with a solid crust is caused by transient pressurization within the drop confined by the crust even under the condition that the boiling of sodium does not occur. If the entrapment of sodium within the drop can occur, the thermal fragmentation due to the transient pressurization induced by overheating of entrapped sodium inside the drop with the crust will be caused prior to the thermal fragmentation due to the pressurization induced by the progression of solid crust inward and the squeeze of inner liquid part of the drop. This indicates the possibility that the metallic alloy fuel on liquid phase formed by metallurgical reactions can be fragmented without occurring the boiling of sodium on the surface of the melt. (authors)