For the understanding of severe accidents in sodium cooled fast reactors (SFR), it is necessary to understand two prototypic accident scenarios such as ULOF (Unprotected Loss of Flow Accident) and UTOP (Unprotected Transient OverPower). As the base knowledge, it is also important to understand high temperature chemical interaction among major core materials such as MOx fuel (MOx: mixed oxide of uranium and plutonium), steel cladding and B₄C neutron absorber have to be investigated. This study aims at providing experimental data on phase formation and phase-stability at various temperature and pressure conditions. A first series of samples containing a mixture of B₄C and steel were prepared to obtain a homogenous metallic solid. In a second step, these metallic samples were mixed and melted with small UO₂ pieces by arc melting. Then these samples underwent a heat treatment at 1900 °C for 1 hour. EDS, EBSD and EPMA analyses were performed to identify the phases formed during the solidification. In addition, thermodynamic calculations were performed for the interpretation of the results, revealing that a carbo-reduction reaction occurs: UO₂ + 2 C = 2 CO + U. A significant amount of uranium from the fuel is dissolved in the metallic liquid phase, leading to the formation of mixed borides (UM₃B₂, UMB₄, UM₄B, M=Fe,Cr,Ni). In comparison with the UO₂/steel interaction, the present results show that the presence of B and C in the melt improves the wetting behaviour of the metallic liquid towards UO₂.

为了理解钠冷快堆（SFR）的严重事故，有必要了解两种原型事故情景，例如ULOF（无保护流量损失事故）和UTOP（无保护瞬态超功率）。作为基础知识，了解主要核心材料之间的高温化学相互作用也很重要，例如必须研究 MOx 燃料（MOx：铀和钚的混合氧化物）、钢包壳和 B ₄ C 中子吸收剂。本研究旨在提供不同温度和压力条件下相形成和相稳定性的实验数据。含有 B ₄混合物的第一组样品制备C和钢以获得均质的金属固体。在第二步中，将这些金属样品与小块 UO ₂混合并通过电弧熔化熔化。然后这些样品在 1900 °C 下进行 1 小时的热处理。进行 EDS、EBSD 和 EPMA 分析以识别凝固过程中形成的相。此外，还进行了热力学计算以解释结果，表明发生了碳还原反应：UO ₂  + 2 C = 2 CO + U。来自燃料的大量铀溶解在金属液相中，导致形成混合硼化物 (UM ₃ B ₂ , UMB ₄ , UM ₄B，M=Fe，Cr，Ni）。与UO ₂ /钢相互作用相比，本结果表明熔体中B和C的存在改善了金属液体对UO ₂的润湿行为。