Possibility of Volume Reduction of Blowdown Tank in Fusion Reactor Safety System

Pressure rise and condensation characteristics during the ingress-of-coolant event (ICE) in fusion reactors were investigated using the preliminary ICE apparatus with a small-scale vacuum vessel (VV), boiler, blowdown tank and isolation valve. High temperature and pressure water was injected from the boiler through piping into the VV which was heated up to 250°C, and pressure and temperature transients in the VV were measured. The pressure increased rapidly with the injection time of water because of the water evaporation. After the VV pressure reached 0.2 MPa, the isolation valve was opened and the VV was connected to the blowdown tank, and then the pressure in the VV decreased suddenly. Two types of blowdown tanks were provided: the first one had a large volume without any cooling systems; and the second one had a small volume and a water jacket to enhance the condensation. From the present experiments, it was found that the most important factors in establishing the pressure rise were flashing evaporation and boiling heat transfer inside the VV. Condensation was very effective in depressurizing the VV.