Abstract

Various numerical models are developed that seek to reproduce, in a simulation instance, the formation and evolution of cracks in the claddings of nuclear fuel elements. The algorithms are based on the cohesive zone method within the finite element framework. When applied to simulations involving fracture mechanics, cohesive elements have various advantages, such as not needing to know the stress state in advance, representing the nucleation of the crack, and being able to reproduce the contact between the crack surfaces after fracture, with numerous application examples for ductile materials, including metals. The models developed were included in the DIONISIO 3.0 nuclear fuel code and compared with analytical test cases, controlled tests of nuclear materials, and a large set of experimental exercises with rods subjected to steep power ramps where breakages are caused due to contact with the pellets. Similarly, these new models were used in controlled experiments where the conditions of an accident type such as a loss-of-coolant accident are reproduced, analyzing the variation of the thermohydraulic, thermomechanical, and structural parameters of a rod.

摘要

开发了各种数值模型，试图在模拟实例中重现核燃料元件包壳中裂纹的形成和演变。这些算法基于有限元框架内的内聚区法。当应用于涉及断裂力学的模拟时，内聚单元具有各种优点，例如不需要事先知道应力状态，代表裂纹的形核，能够再现断裂后裂纹表面之间的接触，具有广泛的应用韧性材料的例子，包括金属。开发的模型包含在 DIONISIO 3.0 核燃料规范中，并与分析测试案例、核材料控制测试、以及大量实验练习，其中杆经受陡峭的功率斜坡，其中由于与颗粒接触而导致破损。类似地，这些新模型也用于受控实验，其中再现了冷却剂丢失事故等事故类型的条件，分析了杆的热液压、热机械和结构参数的变化。