In the recent years, a new concept “passive security” for enhancing the security of reactor was proposed and received more and more attention. It has already been recommended that passive security is the important symbol of the fourth generation of advanced nuclear reactor. Passive security of a reactor In the recent years, a new concept “passive security” for enhancing the security of reactor was proposed and received more and more attention. It has already been recommended that passive security is the important symbol of the fourth generation of advanced nuclear reactor. Passive security of a reactor