基于流固热耦合的燃料元件包壳结构完整性分析

反应堆系统发生瞬态工况时，冷却剂温度的瞬间大幅度变化会对燃料元件包壳结构完整性造成冲击，危及反应堆安全。本文以某压水堆3×3燃料组件为对象，采用流固热耦合方法对冷水事故下燃料组件的流动换热特性和燃料元件包壳温度、变形及应力进行了三维精细化模拟。结果表明:定位格架能够增强燃料棒表面的对流换热强度；包壳变形时向与刚凸接触的一侧折弯，向与弹簧接触的一侧凸起；包壳与定位格架接触部位的温度和最大等效应力随事故时间不断增大，且最大等效应力超过了包壳材料的屈服强度，将发生强度失效，影响其结构完整性。本文研究可为反应堆燃料元件包壳瞬态工况下的完整性评价提供借鉴。 

Structural Integrity Analysis of Fuel Element Cladding Based on Fluid-Solid-Heat Coupling

When a transient condition occurs in the reactor system, the transient and great change of the coolant will impact the structural integrity of the fuel element cladding and endanger the safety of the reactor. In this paper, taking the 3×3 fuel assembly of a PWR as the object, 3D refined simulation of the flow and heat transfer characteristics of fuel assembly and temperature, deformation and stress of fuel element cladding under cold water accident is carried out with the fluid-solid-thermal coupling method. The results show that the spacer grid can enhance the convective heat transfer intensity on the fuel rod surface; When the cladding is deformed, it bends to the side in contact with the rigid convex and bulges to the side in contact with the spring; the temperature and the maximum equivalent stress of the contact part between the cladding and the spacer grid increase with the accident time, and the maximum equivalent stress exceeds the yield strength of the cladding material, which will cause strength failure and affect its structural integrity. The research in this paper can provide reference for the integrity evaluation of reactor fuel element cladding under transient condition.