Acknowledgments. The financial support by the National Natural Science Foundation of China (No. 51674145, 71771084), Postdoctoral Science Foundation of China (No. 2016M600633), Natural Science Foundation of Hunan Province (No. 2017JJ2222), Humanities and Social Science Projects of Ministry of Education (No. 11YJC630207) and Social Science Projects of Hunan Province (No. 16YBA314) are gratefully acknowledged. We would like to express gratitude to the staff in a Chinese nuclear power plant (LingAo-II) for the interviews and investigations, which facilitate the research included in this paper.