NHR200-Ⅱ is a 200 MW nuclear heating reactor. The integrity of the fuel assembly should be ensured during the normal operations and design basis accidents. In the latter cases (e.g. earthquake), its deformation or damage should not prevent the insertion of control rods to shut down the reactor. Meanwhile, during the operating time, there are two aspects that attention should be paid, (i) the mechanical performance of internal core materials might be worsened by the increase of burnup and (ii) dynamic loads involving hydraulic erosion, flow-induced vibration might damage the assemblies. Therefore, the investigation of the dynamic characteristics of the fuel assembly with consideration of burnup effects is necessary. The fuel rod with pellets and cladding was approximated by the beam elements with a circular cross-section applied with calibrated material properties. Connector elements were used to replace the three-arc springs and dimples on the grid and thus simplify the geometry of the spacer grid. The agreements between the detailed and simplified models indicate the equivalence of these two methods. Then two simulations were performed to evaluate the dynamic characteristics of NHR200-II fuel assembly at the beginning of life. The modal simulation of the fuel bundle and channel suggests that the channel could be assumed stationary to the fuel bundle during the dynamic analysis. The seismic simulation conducted in the specific boundary conditions indicates that the integrity of spacer grids can be guaranteed and there was no buckling of the gird. No permanent deformation of the channel was observed, and its relative displacements were sufficiently small to ensure the insertion of control rods. Finally, burnup effects on the structural behavior of the fuel rod are discussed. The initial conditions of NHR200-II fuel assembly and its material properties at different burnup times are provided by referring to two irradiated tests. Various sensitivity analyses had been conducted to evaluate the effects of material properties and pellet-cladding interaction on the resulting failure limit and stiffness of the fuel rod.

NHR200-Ⅱ是一台200兆瓦的核加热反应堆。在正常运行和设计基准事故中，应确保燃料组件的完整性。在后一种情况下（例如地震），其变形或损坏不应阻止控制杆的插入以关闭反应堆。同时，在运行期间，应注意两个方面：（i）燃耗的增加可能会使内芯材料的机械性能变差；（ii）涉及水力侵蚀的动态载荷，可能引起流致振动损坏组件。因此，需要考虑燃耗效应来研究燃料组件的动态特性。带有小球和包层的燃料棒通过带有圆形横截面且施加了标定材料性能的梁单元来近似。连接器元件用于替换栅格上的三弧形弹簧和凹坑，从而简化了间隔栅格的几何形状。详细模型和简化模型之间的协议表明这两种方法是等效的。然后进行了两次仿真，以评估NHR200-II燃料组件在使用寿命开始时的动态特性。燃料束和通道的模态仿真表明，在动态分析期间，可以假定通道相对于燃料束是固定的。在特定的边界条件下进行的地震模拟表明，可以保证间隔格的完整性，并且没有网格的屈曲。没有观察到通道的永久变形，并且其相对位移足够小以确保控制杆的插入。最后，讨论了燃耗对燃料棒结构行为的影响。NHR200-II燃料组件的初始条件及其在不同燃耗时间下的材料特性通过参考两次辐照测试来提供。已经进行了各种敏感性分析，以评估材料性能和药丸-包层相互作用对最终失效极限和燃料棒刚度的影响。NHR200-II燃料组件的初始条件及其在不同燃耗时间下的材料特性通过参考两次辐照测试来提供。已经进行了各种敏感性分析，以评估材料性能和药丸-包层相互作用对最终失效极限和燃料棒刚度的影响。NHR200-II燃料组件的初始条件及其在不同燃耗时间下的材料特性通过参考两次辐照测试来提供。已经进行了各种敏感性分析，以评估材料性能和药丸-包层相互作用对最终失效极限和燃料棒刚度的影响。