U-10Mo合金燃料的辐照脆化和强度退化机理研究

U-10Mo/Al单片式燃料元件具有铀密度高、辐照性能稳定等优点，在研究试验堆中具有良好的应用前景。辐照条件下，U-10Mo合金会产生裂变气体，形成气泡，演化为多孔结构。气孔演化会影响材料辐照蠕变和裂变气体肿胀行为，引发材料辐照脆化和强度退化，进而影响燃料元件堆内安全运行。本研究拟针对U-10Mo合金，建立裂变气体肿胀模型和内聚力模型，发展辐照-降温-卸载后四点弯曲断裂行为计算方法，编写定义材料三维本构关系的子程序；对不同辐照条件下U-10Mo合金四点弯曲试样断裂过程进行数值模拟计算，结合实验结果，验证模型、算法和程序的正确性；分析加载历史对U-10Mo合金宏观弯曲强度的影响，揭示辐照脆化和强度退化机理；进一步分析高燃耗下燃料元件堆内失效行为，解释辐照实验现象。本研究可为分析燃料元件辐照热-力耦合行为和评估元件结构完整性提供理论模型和计算手段，支撑燃料元件及其组件的设计和应用。

U-10Mo/Al monolithic fuel plate has promising applications in research and test reactor due to the advantages of high uranium density and stable irradiation performance. Fission gas atoms will be produced during irradiation and form fission gas bubbles, which leads to a porous structure of U-10Mo alloy. Fission gas swelling and irradiation-induced creep behaviors are affected by the evolution of fission gas bubble, which causes the radiation embrittlement and strength degradation. As a result, the safety operation of fuel plates may be affected in irradiation. In this study, fission gas swelling model and a cohesive zone model are established for U-10Mo alloy. The calculation method for fracture behavior of four-point bending testing after irradiation-cooling-unloading is developed. The user-defined subroutines are programmed to define the three-dimensional constitutive relationship of materials. The four-point bending fracture behaviors of U-10Mo alloy are simulated under different irradiation conditions. Comparing simulation results with experimental data, the effectiveness of the models, algorithms and programs is validated. The influence of loading history on the macroscale bending strength is investigated. The mechanisms of radiation embrittlement and strength degradation are revealed. The irradiation-induced failure behavior of fuel plate in high burnup is further analyzed to explain the experimental phenomena. This study can provide theoretical model and calculation method for analyzing the irradiation-induced thermal-mechanical coupling behavior and evaluating structural integrity of fuel plates, and supports the design and application of U-10Mo/Al monolithic fuel plates and their assemblies.