For a criticality assessment of the fuel debris generated by the Fukushima–Daiichi Nuclear Power Plant accident, knowing the segregation of neutron absorber materials, i.e., Gd, B, and Fe, in the fuel debris is necessary. Although B may mostly evaporate during melting, Fe and Gd are expected to remain in the molten corium. To understand the redistribution behavior of Gd and Fe during the solidification of the molten corium, solidification experiments with simulated corium (containing UO₂, ZrO₂, FeO, and Gd₂O₃ with a small amount of simulated fission products such as MoO₃, Nd₂O₃, SrO, and RuO₂) were performed using a cold crucible induction heating method. The simulated corium was slowly cooled from 2,500 °C and solidified from the bottom to the top of the melt. An elemental analysis of the solidified material showed that the Fe-concentration in the inner region increased up to approximately 3.4 times that in the bottom region. This suggested that FeO might be concentrated in the residual melt and that, consequently, the concentration of Fe increased in the later solidification region. On the contrary, the Gd concentration in the periphery region was found to be approximately 2.0 times higher than that in the inner region, suggesting the segregation of Gd in the early solidified phase and to remain with the residual, UO₂-rich phase even after oxidative losses. No significant segregation was observed for the simulated fission products.

为了对福岛第一核电站事故产生的燃料残渣进行危险性评估，必须了解燃料残渣中中子吸收材料（例如Gd，B和Fe）的偏析。尽管B在熔化过程中可能大部分蒸发，但预计Fe和Gd会残留在熔融的皮质中。要了解Gd和Fe在熔化的皮质的凝固过程中的重新分布行为，可以使用模拟的COR（包含UO ₂，ZrO ₂，FeO和Gd ₂ O ₃以及少量的模拟裂变产物，例如MoO _3）进行凝固实验， Nd ₂ O ₃，SrO和RuO ₂）使用冷坩埚感应加热方法进行。将模拟的皮质从2500°C缓慢冷却，并从熔体的底部到顶部凝固。凝固材料的元素分析表明，内部区域的铁含量增加了约底部区域的3.4倍。这表明FeO可能集中在残留的熔体中，因此，在随后的凝固区域中，Fe的浓度会增加。相反，发现外围区域中的Gd浓度比内部区域中的Gd浓度高约2.0倍，这表明Gd在早期凝固相中偏析并保留了残余的UO _2。富集相，即使经过氧化损失也是如此。对于模拟裂变产物没有观察到明显的偏析。