The financial support by the National Natural Science Foundation of China (Grant No. 71371070, 71301069, 51674145, 71501068, 71771084) and Scientific Research Program supported by Lingdong Nuclear Power Plant (Grant No. KR70543), Postdoctoral Science Foundation of China (Grant No. 2016M600633), Natural Science Foundation of Hunan Province (Grant No. 2017JJ2222), Humanities and Social Science Projects of Ministry of Education (Grant No. 11YJC630207), Program of China Scholarship Council (CSC), Social Science Projects of Hunan Province (Grant No. 16YBA314) and Science and Technology Program of Hunan Province, China (Grant No. 2016WK2006) 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. The anonymous reviewers and the editor of this paper are also gratefully acknowledged for their constructive comments and suggestions.