Ti3SiC2/UO2燃料芯块的设计制备及热物理性能研究

UO2 is widely ultilized as nuclear fuel in commercial reactors. However, the low thermal conductivity decreases the safety of the reactors in accidient condition. This project is aimed at the high-performance accident-tolerant fuel utilized in next generation nuclear reactors. Based on the high melting point, excellent irradiation resistance, well thermal conductivity at elevated temperature and good thermal expansion compatibility with UO2, Ti3SiC2 is introduced into UO2 to improve the thermal conductivity on the prediction of keeping its own characteristic.. Ti3SiC2/UO2 pellets with higher thermal conductivity than traditional UO2 are expected to be fabricated through the optimized SPS technique in this project. The relationship between the sintering parameters and microstructure will be explored to study the sintering mechanism of Ti3SiC2/UO2. The thermal conductivity, thermal expansion property and melting point of Ti3SiC2/UO2 will be systematically studied. The safety of Ti3SiC2/UO2 near accident condition will be evaluated from the angle of thermal physical properties. The heat conduction mechanism of Ti3SiC2/UO2 will be discussed in depth. The heat conduction characteristic of the composites will be researched through H&J model or finite element method. Finally, this project can provide a new route to enhance the thermal conductivity of UO2 and improve the safety of fuel system in reactors.

UO2作为核燃料材料广泛应用于商业反应堆中，然而UO2的低热导率使得反应堆在事故工况下的安全性显著下降。面向新一代核反应堆对高性能事故容错核燃料的迫切需求，本项目结合Ti3SiC2的高熔点、优异的耐辐照特性、良好的高温热导率以及与UO2良好的热膨胀匹配性，向UO2中添加Ti3SiC2进行改性，从而在保持UO2特性的同时提升其热导率。. 本项目拟通过优化设计SPS烧结工艺，制备得到导热性能优于传统UO2的新型Ti3SiC2/UO2芯块。探索烧结工艺与微观组织的关系，阐明Ti3SiC2/UO2的烧结机制。系统研究Ti3SiC2/UO2的热导率、热膨胀性能和熔点，从热物理性能的角度评价Ti3SiC2/UO2在近事故工况下的安全性能。深入讨论其导热机制，采用H&J模型或有限元方法分析复合材料的导热特性，为改进UO2热导率，提高反应堆燃料组件的安全性能提供一条新途径。

现阶段商业核反应堆中广泛应用的核燃料芯块材料是UO2。UO2具有高熔点、辐照稳定性好、耐水蒸气腐蚀以及与包壳材料相容性好等优点。然而UO2热导率低，工作时燃料芯块内部温度梯度陡峭，热应力显著，存在安全隐患。.为提升UO2的热导率，本项目向UO2中引入Ti3SiC2。Ti3SiC2具有高熔点、优异的抗辐照性能、良好的力学性能、导热性能、抗氧化性和耐蠕变性等，与UO2对高导热第二相的需求相契合。项目设计、制备出连续分布Ti3SiC2/UO2复合芯块(CO-Ti3SiC2/UO2)和半连续分布Ti3SiC2/UO2复合芯块(SC-Ti3SiC2/UO2)，系统研究了其烧结机制、热物理性能、导热机制和导热模型。主要研究结果如下：.(1) CO-Ti3SiC2/UO2复合芯块的烧结行为呈明显的阶段性，包括轻微膨胀、快速致密化、慢速致密化、烧结暂停、慢速致密化、稳定化6个过程。.(2) 为简化制备工艺，同时保持热导率增强效果，设计制备了SC-Ti3SiC2/UO2复合芯块。结合H-J模型和DEM模型描述了SC-Ti3SiC2/UO2和CO-Ti3SiC2/UO2的导热特性。理论计算和实验结果均表明，SC-Ti3SiC2/UO2和CO-Ti3SiC2/UO2的热导率差别很小。.(3) Ti3SiC2/UO2复合芯块的高温热导率相对于纯UO2大幅提高，有助于提升燃料芯块的安全性。.(4) CO-Ti3SiC2/UO2的热导率提升是由于连续Ti3SiC2结构提供了导热通道。SC-Ti3SiC2/UO2的热导率提升一方面是由于半连续Ti3SiC2结构提供了导热通道，另一方面是由于少量弥散于UO2的Ti3SiC2颗粒提升了基体热导率。