中子衍射在不锈钢材料焊接应力辐照松弛行为的研究

The material reliability plays an important role in nuclear power plant safety. Especially in the center of the plant, the material is affected by the high radiation, and that will make the material degraded. The failure of the material may lead to serious accident; do much harm to the people and environment. The experience of the running nuclear power plant shows that stress corrosion crack (SCC) is one of the major reasons for the plant failure accident.SCC growth occurs around a welded zone because of its residual tension stress, so that stress is one of the important factors for evaluation of SCC growth. Therefore, stress evaluation is important for accurate prediction of SCC growth and for evaluation of health of nuclear reactor components. The neutron radiation can induce stress relaxation in reactor components. And the experiment data will help to study the safety and severice life of the reactor componments.The objectives of this study are to obtain radiation-induced stress relaxation data in welded stainless steel and to evaluate the radiation-induced stress relaxation behavior. Neutron diffraction is the unique non-destructive method, which can facilitate 3-D mapping of residual stress in a bulk component up to now. And it is an ideal tool to make further research on characterizing the residual stress and evaluating the service life of engineering material, which promises encouraging prospects for industrial application. The neutron diffraction will be applied to study the radiation-induced stress relaxation behavior, and the relationship between neutron radiation and stress relaxation will be characterized. The study result will be used for reference about the safety evaluation of nuclear power plant.

核电站的安全性很大程度上取决于核电材料在高温高压水和辐照条件下长期服役的可靠性。特别是在核岛中工作的材料经受着辐照的影响，会导致材料性能的不断退化。在此特定环境中服役的关键材料的失效往往会导致灾难性事故，危及民众和环境的安全。国际上核电先进国家长期运行的经验表明，以应力腐蚀开裂为代表的环境促进开裂已成为压水堆构件失效的主要原因之一。残余拉应力的存在是导致应力腐蚀裂纹在焊接区域附近生成并扩展的关键因素,应力分布及其演化是裂纹生长精确预算和核电站组件质量安全评估的重要依据,中子辐照会引起应力松弛行为，与部件的质量、安全和寿命密切相关。拟利用中子衍射在工程部件三维、无损、深度残余应力测量分析的独特优势，对不锈钢焊接应力辐照松弛行为进行系统的研究，给出中子辐照与应力松弛之间的定量关系。为深入研究关键材料残余应力分布和演化与腐蚀开裂的内在联系机理，以及核电站长期运行的安全性、可靠性评估提供参考数据。

首先建立起深度三维应力测试分析的方法学。为了模拟真实的样品使用环境，考虑到反应堆一回路部件处于高温环境下，研究并开发了一种镜面高温炉装置。该镜面高温炉用于中子衍射谱仪样品的原位高温加载实验。完成了一种屏蔽装置的详细设计，该装置专用于放射性样品的中子衍射残余应力三维无损测量实验。主要功能是对样品的核辐射进行屏蔽防护，满足样品转移时周围的安全剂量要求，同时满足中子残余应力三维测试的技术要求。利用该装置，可实现一定剂量的反应堆内放射性样品的残余应力中子衍射无损检测。提出一种测量Soller准直器发散度的新的理论方法，建立新的数学模型，通过理论计算得到描述实验的响应函数，并开展一系列实际中子束流发散度实验测量，利用理论函数拟合实验数据得到相应发散角的精确值。全面理解中子束流的准直性能，为优化中子散射谱仪的分辨率提供参考。在中子光路调试和优化过程中，为了精细检测中子光路微弱的中子泄露信号，发展了一种新方法，专用于中子光路上的屏蔽泄露检测。为了实现中子残余应力数据的智能化测试分析流程，数据获取和收集过程需相应的运动控制配合，通过相应软硬件收集中子衍射、样品坐标以及样品环境相关数据，按一定格式进行显示和保存。数据分析处理软件主要完成原始数据的修正，数据拟合，计算和显示，远程监控等功能。建立起基本的中子谱仪光路的优化模拟技术方法。利用中子衍射残余应力测试谱仪，开展了不锈钢焊接材料的残余应力测试分析。获得了相关材料的残余应力值，测得的数据表明，相关数据可以为焊接工艺的改进提供参考。