In order to clarify the fragmentation of molten core structural material (stainless steel) and molten metallic fuel and claddings on liquid phase formed by metallurgical reactions (liquefaction temperature = 650°C) during core disruptive accidents (CDAs), the present study focuses on the fragmentation of single molten stainless steel (316SS) and aluminum droplet penetrating a sodium pool. The temperatures of 3–5g molten aluminum droplets were 1002 to 1399°C, and the sodium pool was about 300°C. The instantaneous contact interface temperatures (Ti) between the molten aluminum droplets and liquid sodium were calculated to be from 741°C below the boiling point of sodium (Tc,bp) to 1019°C above Tc,bp. The temperatures of 5g molten 316SS droplets were 1510 to 1706°C, and the temperatures of sodium pool vary about 300–400°C. The Ti values between the molten 316SS droplets and liquid sodium were calculated to be from 916 to 1082°C. Fragmentation of the single molten aluminum droplet was clearly observed even at TiTc,bp. When Ti is approximately equal to or higher than the boiling point, the intensive fragmentation of droplet was clearly observed independent of Wea condition. Fragmentation of the single molten 316SS droplet was clearly observed even at Ti below its melting point. The Dm values of aluminum and 316SS droplets with relatively high Wea tend to be lower than those of droplets with relatively low Wea under the relatively low Ti condition. These results indicate the fragmentation of the molten core structural material and eutectic alloy fuels in liquid phase formed by the metallurgical reactions could possibly occur under the low Ti condition below and above the sodium boiling point, which is promising to assure the termination of accidents in CDAs and useful to the core design with enhanced safety in FBRs.

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