Wang Jiamin, Feng Shanglei, Yang Yingguo, Tang Hui, Liu Xiangdong, Xia Huihao, Wang Yong, Zhou Xingtai
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 2019 Jialuo Road, Shanghai 201800, China.
School of Physics and State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China.
ACS Omega. 2019 Feb 27;4(2):4304-4311. doi: 10.1021/acsomega.8b03329. eCollection 2019 Feb 28.
Owing to the inhomogeneous distribution of FLiNaK salt impregnated into graphite which is observed by scanning electron microscopy and an element probe micro-analyzer, a map scan of in situ real-time tensile synchrotron-based two-dimensional X-ray diffraction (2D-XRD) at several fixed external forces was implemented to reveal the local microstructure evolution of graphite and FLiNaK salt. Notably, a stress concentration area (SCA), that is, the main interaction area between graphite and salt, was found and then transformed from one region to another region because of the unbalanced squeeze interaction between graphite and FLiNaK salt with the increase of external force. During the external stress load process, a smaller grain size, poorer crystallinity of graphite and a larger grain size, better crystallinity of FLiNaK salt appear in the SCA; meanwhile, the changes of crystallographic preferred orientation of FLiNaK salt domains in SCA imply that the external load force makes better the ordered stacking of the larger crystal grains of the FLiNaK salt impregnated into graphite. Most importantly, we have found for the first time that the fracture position of graphite impregnated with FLiNaK salt always occurs near the SCA rather than at a fixed region under the external stress load. Thus, the present study not only helps to reveal the interaction mechanism between graphite and FLiNaK salt under the external stress load but also contributes to accurately predict and analyze the stress state of components, which would have an effective impact on the design of a molten salt reactor and the reliability of the component safety assessment.
通过扫描电子显微镜和元素探针微分析仪观察到，由于浸渍在石墨中的FLiNaK盐分布不均匀，因此在几个固定外力下进行了基于同步辐射的原位实时拉伸二维X射线衍射（2D-XRD）的图谱扫描，以揭示石墨和FLiNaK盐的局部微观结构演变。值得注意的是，发现了一个应力集中区域（SCA），即石墨与盐之间的主要相互作用区域，随着外力增加，由于石墨与FLiNaK盐之间的挤压相互作用不平衡，该区域从一个区域转变为另一个区域。在外部应力加载过程中，SCA中出现了较小的石墨晶粒尺寸、较差的石墨结晶度以及较大的FLiNaK盐晶粒尺寸、较好的FLiNaK盐结晶度；同时，SCA中FLiNaK盐畴的晶体学择优取向变化表明，外部加载力使浸渍在石墨中的FLiNaK盐的较大晶粒的有序堆积更好。最重要的是，我们首次发现，在外部应力加载下，浸渍有FLiNaK盐的石墨的断裂位置总是出现在SCA附近，而不是在固定区域。因此，本研究不仅有助于揭示外部应力加载下石墨与FLiNaK盐之间的相互作用机制，还有助于准确预测和分析部件的应力状态，这将对熔盐反应堆的设计和部件安全评估的可靠性产生有效影响。
