Investigations on the morphology and phase equilibrium characteristics of corium were performed by a series of experiments in parallel with thermodynamic phase equilibrium analyses. Melting and solidification experiments were performed using corium consists of U, Zr, ZrO₂, SS, and B₄C. TROI-49 and TROI-50 experiments with corium compositions representing Pressurized Water Reactor (PWR), whose compositions are similar to those of MA-3 and MA-4 of OECD MASCA (Material Scaling) Program while amount of mass is 5 times more, resulted in two-layered structure with oxide rich layer on top of metal rich layer. Experiments of FK-1 and FK-2 with a mixture of UO₂, ZrO₂, Zr, SS and B₄C at a representative Fukushima Daiichi Nuclear Power Plant (FDNPP) corium composition resulted in a formation two-layered structure of corium with upper layer rich in metal and lower layer rich in oxide. Zirconium diboride phase trapped boron and mainly distributed in the metallic layer. Predictions by thermodynamic calculations for the equilibrium phase distribution and chemical compositions of each phase using the NUCLEA thermodynamic database with a focus on U-Zr-O-Fe system were in good agreement with the experimental results. Agreement in terms of U/(U+Zr) was quite close while there were dispersions in oxygen and steel components. The temperatures for the formation of two immiscible liquids calculated by the NUCLEA for FK-1 and FK-2 was 300 K higher than the experimental observation. This point has to be looked at for improving the NUCLEA models for corium containing B₄C, by introducing a non-zero boron solubility in the ceramic phase. The agreement between the NUCLEA predictions and the results of experiments clearly indicate that thermodynamic equilibrium phases play an important role in governing the core damage progression, which is important not only for the severe accident management but also for decommissioning and defueling process for the Fukushima Daiich damaged reactors.

通过一系列与热力学相平衡分析相平行的实验，对皮质的形态和相平衡特性进行了研究。使用由U，Zr，ZrO ₂，SS和B ₄ C组成的皮质进行熔化和固化实验。TROI-49和TROI-50实验使用代表压水堆（PWR）的皮质成分进行，其成分与OECD MASCA（材料缩放）程序的MA-3和MA-4的质量是其5倍以上，导致了两层结构，在富金属层的顶部具有富氧化物层。UO ₂，ZrO ₂，Zr，SS和B ₄的混合物对FK-1和FK-2的实验在具有代表性的福岛第一核电站（FDNPP）中，C形成了两层结构的皮质，其上层富含金属，下层富含氧化物。二硼化锆相捕获了硼，并且主要分布在金属层中。使用NUCLEA热力学数据库，以U-Zr-O-Fe系统为重点，通过热力学计算对各相的平衡相分布和化学成分进行的预测与实验结果非常吻合。以U /（U + Zr）表示的协议非常接近，同时在氧气和钢成分中存在分散。由NUCLEA计算得出的FK-1和FK-2两种不混溶液体的形成温度比实验观测值高300K。₄ C，通过在陶瓷相引入非零硼溶解性。NUCLEA预测与实验结果之间的一致性清楚地表明，热力学平衡阶段在控制核心破坏进程中起着重要作用，这不仅对严重事故管理，对于福岛第一核电站的退役和加油过程也很重要。反应堆。