[1] Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China
[2] Dept. II of Nuclear and Radiation Safety Regulation of Min. of Environ. Protection of P. R. China, Beijing 100035, China
[3] China Institute of Atomic Energy, Beijing 100035, China
[4] China Nuclear Power Design Co. Ltd. (Shenzhen), Shenzhen, Guangdong, 518031, China
[5] Nuclear and Radiation Safety Center of Ministry of Environmental Protection of P. R. China, Beijing 100082, China