A high-pressure polymerization system comprising a) a continuously operable polymerization reactor having a reactor inlet and having a reactor outlet and b) a reactor blow down system adapted and arranged to be in fluid communication with the polymerization reactor, the reactor blow down system comprising b1) a reactor blow down vessel, which has an essentially circular design over a major portion P having a length L, a diameter D and a L/D-ratio in the range from 1.75 to 10.0, preferably in the range from 2.0 to 6.0, and in particular in the range from 2.0 to 4.0, and which contains an aqueous quenching medium, b2) one or more release lines, which connect the polymerization reactor with the reactor blow down vessel and which comprise a release line outlet, for expanding a content of the high-pressure polymerization system comprising polymer and gaseous components into the reactor blow down vessel, where the release line outlets, are located above a maximum level for the aqueous quenching medium, and b3) one or more first emergency valves arranged in the one or more release lines and adapted to open and close a fluid communication between the polymerization reactor and the reactor blow down system, wherein the release line outlets, each have a joining piece,, which has a central axis, and which is arranged in a way that an angle (α) formed between the central axis, of the joining piece, and a tangent being located at the intersection of the central axis, with the circular periphery of the major portion P of the reactor blow down vessel and having the same inclination as the central axis, with respect to the horizontal plane containing this intersection is in the range from 5° to 70°, preferably in the range from 10° to 60°, and more preferably in the range from 15° to 50°, and wherein the reactor blow down vessel further comprises a vent stack for venting the gaseous components into the atmosphere, the vent stack containing a constricted section, wherein the vent stack is a vertical tube having an inner diameter from 0.4 m to 1.4 m and the constricted section of the vent stack has a smaller inner diameter so that the open cross-sectional area at the constricted section is from 10% to 60% of the open cross-sectional area of the vertical tube. a) a continuously operable polymerization reactor having a reactor inlet and having a reactor outlet and b) a reactor blow down system adapted and arranged to be in fluid communication with the polymerization reactor, the reactor blow down system comprising b1) a reactor blow down vessel, which has an essentially circular design over a major portion P having a length L, a diameter D and a L/D-ratio in the range from 1.75 to 10.0, preferably in the range from 2.0 to 6.0, and in particular in the range from 2.0 to 4.0, and which contains an aqueous quenching medium, b2) one or more release lines, which connect the polymerization reactor with the reactor blow down vessel and which comprise a release line outlet, for expanding a content of the high-pressure polymerization system comprising polymer and gaseous components into the reactor blow down vessel, where the release line outlets, are located above a maximum level for the aqueous quenching medium, and b3) one or more first emergency valves arranged in the one or more release lines and adapted to open and close a fluid communication between the polymerization reactor and the reactor blow down system, b1) a reactor blow down vessel, which has an essentially circular design over a major portion P having a length L, a diameter D and a L/D-ratio in the range from 1.75 to 10.0, preferably in the range from 2.0 to 6.0, and in particular in the range from 2.0 to 4.0, and which contains an aqueous quenching medium, b2) one or more release lines, which connect the polymerization reactor with the reactor blow down vessel and which comprise a release line outlet, for expanding a content of the high-pressure polymerization system comprising polymer and gaseous components into the reactor blow down vessel, where the release line outlets, are located above a maximum level for the aqueous quenching medium, and b3) one or more first emergency valves arranged in the one or more release lines and adapted to open and close a fluid communication between the polymerization reactor and the reactor blow down system, wherein the release line outlets, each have a joining piece,, which has a central axis, and which is arranged in a way that an angle (α) formed between the central axis, of the joining piece, and a tangent being located at the intersection of the central axis, with the circular periphery of the major portion P of the reactor blow down vessel and having the same inclination as the central axis, with respect to the horizontal plane containing this intersection is in the range from 5° to 70°, preferably in the range from 10° to 60°, and more preferably in the range from 15° to 50°, and wherein the reactor blow down vessel further comprises a vent stack for venting the gaseous components into the atmosphere, the vent stack containing a constricted section, wherein the vent stack is a vertical tube having an inner diameter from 0.4 m to 1.4 m and the constricted section of the vent stack has a smaller inner diameter so that the open cross-sectional area at the constricted section is from 10% to 60% of the open cross-sectional area of the vertical tube.