Solidification behavior of molten core oxidic materials using cold crucible induction heating technique

Sato, Takumi ; Sudo, Ayako ; Nagae, Yuji 

In the accident of Fukushima Daiichi Nuclear Power Station, various reactor structures melted and formed fuel debris, which accumulated in the primary containment vessel region. This fuel debris is considered to have a heterogeneous distribution of components at different locations. Understanding the distribution of GdO, which may behave as potential neutron absorber materials in the fuel UO, is especially important from the viewpoint of criticality safety for fuel retrieval. We conducted solidification tests of reactor materials to investigate component segregation and solidification behavior in fuel debris using a Cold Crucible Induction Heating technique at the Research Centre (CVR) in Czech Republic. In the tests, GdO was concentrated in the periphery of the sample, suggesting that it may segregate in the early solidification region. On the other hand, Fe was concentrated in the central region, i.e., in the late solidification region. Fe is considered to be concentrated in the late solidification position because, thermodynamically, it is distributed to the liquid phase during the solidification process. No significant segregation was observed in the simulated fission products.