锆合金包壳管辐照-氢致多场耦合开裂行为的三维数值模拟研究

The zircaloy cladding tubes are the first barrier to prevent nuclear leakage, and it is crucial to guarantee their structural integrity after hydrogen pick-up. In this study, with comprehensively considering the irradiation effects, the hydrogen induced expansion and hardening effect together with the degradation effect on the creep rate, we will develop the multi-field coupling computation models under general loading conditions, pertaining to the hydrogen concentration in solid solution, the hydride volume fraction and mean orientation, the temperature and mechanical fields. The cohesive zone model is to be established through combination of experimental results and numerical ones to simulate the fracture process in the mechanical fields, with the effects of irradiation dose, hydride volume fraction, hydride mean orientation, stress state and damage accumulation involved. The equivalent integral weak forms, the non-linear finite element equations and iterative schemes for the above multi-fields are to be respectively derived out together with the multi-field coupling computation algorithms, based on which, through programming we plan to obtain all the finite element procedures in the FEPG software platform for the three-dimensional simulation of the hydride induced cracking behavior in the cladding tubes. With the numerical simulation results compared with the experimental results, the effectiveness of the multi-field coupling models, computation methods and procedures are to be validated. For zircaloy cladding tubes, the effects are to be calculated and analyzed of texture factors, irradiation conditions, thermo-mechanical loading histories and the crack sizes on the hydride induced cracking behavior. This research can supply computation methods and a calculation software for the structural integrity evaluation and fracture mechanism analysis of zircaloy cladding tubes during reactor operation as well as under long-term storage of spent nuclear fuels. This research is of great scientific significance, and also has important engineering application values.

锆合金包壳管是防止核泄漏的第一道屏障，确保其吸氢后的结构完整性至关重要。本研究综合考虑锆合金的辐照效应、氢致膨胀、硬化和蠕变效应，发展固溶氢原子浓度、氢化物体积分数及平均取向、温度、力学各场量相互耦合的计算模型。结合试验数据分析和数值模拟，建立受应力状态、辐照剂量、氢化物体积分数及取向影响的内聚力模型，引入损伤累积效应模拟断裂过程。推导各物理场所满足的等效积分弱形式、非线性有限元方程组及迭代求解格式，建立多场耦合计算方法，编程获得对包壳管多场耦合下的氢致断裂行为进行三维模拟的有限元程序。对比数值模拟结果与试验测试结果，验证多场耦合模型、计算方法及程序的正确性。计算分析织构因子、辐照条件、热-力学载荷历史、裂纹尺寸对锆合金包壳管氢致开裂行为的影响。本研究可为锆合金包壳管堆内运行和乏燃料长期储存阶段的结构完整性评价和破坏机理分析提供计算方法、软件支持，具有科学意义和重要工程应用价值。

锆合金构件在现役反应堆得到了广泛应用，在未来先进核反应堆中也具有良好的应用前景。辐照氢脆效应对锆合金构件的服役安全性及乏燃料储存阶段的结构完整性造成了极大的威胁。本研究综合考虑锆合金材料的辐照效应、氢致膨胀、硬化和蠕变效应，获得了固溶氢原子浓度、氢化物体积分数及平均取向、温度、力学各场量相互耦合的理论模型，形成了适合于分析多种锆合金材料辐照氢致耦合断裂行为的理论框架。利用内聚力模型描述预开裂面的本构，创新性地考虑了应力状态、辐照剂量、氢化物体积分数及平均取向的影响，并引入了损伤的累积效应。基于各场量所满足的微分控制方程组，推导出对应的等效积分弱形式及有限元方程，形成迭代求解格式，编程实现了锆合金包壳等材料的辐照氢致多场耦合行为的有限元模拟，能够模拟出亚临界裂纹扩展的特征。所获得的氢致延迟开裂速率等结果与多种锆合金材料的试验测试结果能够很好地符合，验证了本研究所获得的模型、算法及程序的合理有效性。计算分析了材料织构因子、辐照条件、热-力学加载历史、裂纹形状尺寸对锆合金包壳管辐照氢致开裂行为的影响规律及机制。研究结果表明，在相同的应力强度因子作用下， (1) 环向织构因子的增加致使材料的屈服强度和预开裂面的内聚强度增大，从而提高了氢浓度梯度和静水应力梯度，驱使氢原子加速扩散至裂纹尖端附近、导致氢化物析出，减小了每次开裂的等待时间及脆化开裂区域的长度，总体上增大了氢致延迟开裂的速率；(2) 辐照剂量的增加也会导致材料的屈服强度和内聚强度增加，最后增大了氢致延迟开裂速率；在所考察的参数范围内，每次的脆化开裂区域的长度随辐照剂量增加、等待时间缩短；对于某些锆合金材料，辐照剂量会影响氢原子的扩散系数，此机制会成为速率随辐照剂量增加而增大的主控机制；(3) 热-力学加载的历史对氢致多场耦合断裂行为也会产生重要影响，从高温降低到测试温度会致使氢原子的固溶度升高、增大氢浓度梯度，促使每次开裂的等待时间缩短、开裂速率增加；(4) V型裂纹的切口角度越小，第一次开裂所需的等待时间越短；第一次开裂之后的多场耦合行为相似，所以，氢致延迟开裂的速率相近。本研究为多种锆合金构件的先进制造、优化设计和性能评估提供了理论模型和分析手段，具有重要的科学意义和工程应用价值。