Combined peridynamics and finite element crystal plasticity modelling of the oxidation of zirconium alloys

该项目涉及在微尺度上模拟核燃料包层上不断增长的氧化锋面。这是一个复杂的多物理过程，涉及温度和应力梯度下离子物种的扩散，以及脆性氧化物相中裂纹形成的机制。裂纹的形成既可以增加(通过垂直破裂)，也可以阻碍(通过横向破裂)氧分子和水分子进入金属-氧化物界面。最重要的是，裂解解除了随着氧化物变厚而积累的应力。从机理上理解氧化过程是该项目的目标。这将反过来为氧化物生长行为的更高尺度模型提供信息，这最终可以决定覆层，从而决定燃料寿命。提高燃料寿命既提高了工厂运营的经济性，又减少了废物负担。为此，我们将使用两种最终将结合在一起的技术：(1)周期动力学，这是一种非局部伪无网格方法，可以模拟氧化物相中的脆性开裂，以及(2)因为这是一个微尺度现象，所以我们将使用有限元晶体塑性模型来模拟底层的锆金属。这些方法加在一起，将给出目前为止最完整的燃料包壳氧化过程模型。

This project involves modelling the growing oxidation front on nuclear fuel cladding at the microscale. This is a complex multi-physics process involving diffusion of ionic species under temperature and stress gradients coupled to the mechanics of crack formation in the brittle oxide phase. Crack formation can both increase (through vertical cracking) or hinder (through lateral cracking) the oxygen and water molecule ingress to the metal-oxide interface. On top of this the cracking relieves the stresses that build up as the oxide thickens. Mechanistic understanding of the oxidation process is the aim of the project. This will in turn inform higher scale models of the oxide growth behaviour, which can ultimately determine the cladding and hence fuel life. Improving fuel life improves both the economics of plant operation and reduces the waste burden. To do this we will use two techniques that will ultimately be coupled together: (1) peridynamics, which is a non-local pseudo-meshless method that can model brittle cracking in the oxide phase, and (2) because this is a microscale phenomenon we will use finite element crystal plasticity modelling for the underlying zirconium metal. Together these methods will give the most complete model yet of the oxidation process of fuel cladding at this scale.