Multiphase flow in passive safety system with natural power. Heat removal using phase change

In order to mitigate severe accidents of nuclear power plants, a passive safety system is one of influential measures. As the passive safety system uses natural power such as gravity and/or phase changes instead of electrical power, multiphase flows appear in the system. In this paper, multiphase flows in the passive safety system are introduced from several developments. First, a PCCS uses condensation in heat transfer tubes to remove decay heat. Second, oscillated water-vapor multiphase flow can provide cooling water to the heated surface of core-catcher cooling channel. At last, three-phase flows comprising gases, solid aerosols and liquids in safety measures against severe accidents are mentioned. (author)