Solidification behavior of the simulated oxide debris

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

In order to obtain the knowledge on the phase relationship and stratification behavior of oxide debris under the slow solidification condition, liquefaction/solidification tests of simulated oxide debris were performed by using a high frequency induction furnace. As the oxides components from the core melt and structural materials, sintered pellets of UO-ZrO-sim-FPs and powder of FeO and BC were prepared. The powder mixture and crashed sintered oxides were heated to 2600C in Ar atmosphere in the first step (partial liquefaction), and then solidified at two different cooling rates; furnace cooling (No.1) and slow cooling (5C /min, No.2). For the corium microstructure study, solidified samples were subjected to elemental analysis by SEM/EDX. Cross sectional images of both samples showed that the oxide layer and metallic layer were separately solidified. EDX analysis of oxide layer of No.1 sample revealed four phases; (UZrFe)O, (ZrUFe)O, ZrO and Fe metal. The tendency of re-distribution of oxide elements observed in No.2 was similar to that of No.1, however, the grain-growth of (Zr,U)O phase occurred at the bottom region of the oxide layer. In these results, the phases detected in both samples were in reasonable accordance with those evaluated by the UO-ZrO-FeO phase diagram.