核反应堆刚凸-包壳微动损伤裂纹行为研究

Study on fretting damage crack behavior of dimple-cladding in nuclear reactor

核燃料棒组件中包壳管与刚凸之间发生的微动行为可能引起组件的破坏失效,严重时会威胁反应堆安全。为此,以核燃料棒中刚凸-包壳结构为研究对象,针对其在微动行为下裂纹的萌生及扩展问题,通过有限元仿真的方法展开研究。研究结果表明:在微动过程中包壳管接触区始终处于受压状态,滑移区中裂纹受剪应力控制,在包壳管涂层基体界面开裂并沿着界面蜿蜒扩展,导致涂层剥离;在混合区和部分滑移区中,裂纹受剪应力和正应力同时作用,起裂于包壳表面或次表面向内部扩展;刚凸-包壳结构微动行为中,剪应力是导致包壳管损伤的主要因素,对裂纹的萌生和扩展起主导作用。

The fretting behavior between the cladding tube and the rigid convex in the nuclear fuel rod assembly may cause the failure of the assembly,and even threaten the safety of the reactor.This paper takes the dimple-cladding structure in the nuclear fuel rod assembly as the research object to address the crack initiation and propagation under the fretting behavior of rigid-cladding.It employs the finite element simulation method.Our results show the contact area of the cladding tube is consistently under pressure during the circular moving fretting process.The crack is controlled by shear stress in the slip regime,which initiates at the interface between cladding coating and substrate and propagates along the interface,even causing the coating delamination.While in the mix regime and partial slip regime,cracks initiate at the surface or sub-surface of the cladding and propagate to the interior of the cladding,which are controlled by both shear stress and normal stress.Our results show the shear stress is the main cause of the damage of the cladding tube,and plays a primary role in the initiation and propagation of cracks in the fretting behavior of rigid-cladding structures.