Abstract: The depressurization process of supercritical water has a significant influence on the safety of SCWR. The paper carried out the experimental study of the top and bottom vented blowdown processes of supercritical freon (R134a). The investigation focuses on pressure and temperature transients. The effect of initial fluid conditions, orifice diameter on depressurization behavior was experimentally analyzed. During the isentropic change, it is observed that the pressure at which two phases appear depends mainly on the initial fluid condition and depressurization mass flow rate. There is almost no axial temperature gradient during the isentropic process.