Fundamental study on segregation behavior in U-Zr-Fe-O system during solidification process

Sudo, Ayako ; Mizusako, Fumiki*; Hoshino, Kuniyoshi*; Sato, Takumi ; Nagae, Yuji ; Kurata, Masaki 

Cooling rate of molten core materials during solidification significantly affects the segregation of major constituents of fuel debris. To understand general tendency of the segregation, liquefaction/solidification tests of simulated corium (UO, ZrO, FeO, BC and sim-FP oxides) were performed. Simulated corium was heated up to 2600C under Ar atmosphere and then cooled down with two different cooling processes; furnace cooling (average cooling rate is approximately 744C/min) and slow cooling (cooling rate in 2600C2300C is 5C/min and in 2300C1120C is approximately 788C/min). Element analysis detected three oxide phases with different composition and one metal phase in both solidified samples. Solubility of FeO in these oxide phases was mostly fixed to be 125at% in both samples, which is in reasonable accordance with the value estimated from UO-ZrO-FeO phase diagrams. However, a significant grain-growth of one oxide phase, rich in Zr-oxide, was detected only in the slowly cooled sample. The composition of this particular oxide phase is comparable to the initial average composition. The condensation is considered to be caused by the connection of remaining liquid agglomerates during slow solidification.