A tube bundle reactor for catalytic gas phase reactions, having - a bundle of reaction tubes, which is enclosed by a cylindrical reactor shell, which forms a shell chamber, in which a heat transfer medium flows around the reaction tubes, wherein a reaction gas flows through the reaction tubes; - a heat transfer medium advance annular passage and a heat transfer medium return annular passage, which enclose the reactor shell in each case in an end region of the cylinder and which are in flow connection with the shell chamber via a multiplicity of shell openings; - exactly one pump located outside, the inlet of which is connected to the heat transfer medium return annular passage and the outlet of which is connected to the heat transfer medium advance annular passage and which circulates the heat transfer medium in a circuit through the advance annular passage, the shell chamber and the return annular passage; - a main heat exchanger located outside connected into the circuit, the outlet of which is connected to the inlet region of the pump and via which a part of the heat transfer medium flow is conducted into the inlet region as heat exchanger return, - wherein the pump comprises a pump housing with a propeller and the pump housing in the inflow to the propeller has a concentric region directed axially upwards, characterized in that - a second heat transfer medium return annular passage encloses the region of the pump housing that is directed upwards and is in flow connection with the inflow to the propeller via a multiplicity of pump housing openings, which are evenly distributed over the circumference of the pump housing, and - the outlet of the main heat exchanger is connected to the second heat transfer medium return annular passage. - a bundle of reaction tubes, which is enclosed by a cylindrical reactor shell, which forms a shell chamber, in which a heat transfer medium flows around the reaction tubes, wherein a reaction gas flows through the reaction tubes; - a heat transfer medium advance annular passage and a heat transfer medium return annular passage, which enclose the reactor shell in each case in an end region of the cylinder and which are in flow connection with the shell chamber via a multiplicity of shell openings; - exactly one pump located outside, the inlet of which is connected to the heat transfer medium return annular passage and the outlet of which is connected to the heat transfer medium advance annular passage and which circulates the heat transfer medium in a circuit through the advance annular passage, the shell chamber and the return annular passage; - a main heat exchanger located outside connected into the circuit, the outlet of which is connected to the inlet region of the pump and via which a part of the heat transfer medium flow is conducted into the inlet region as heat exchanger return, - wherein the pump comprises a pump housing with a propeller and the pump housing in the inflow to the propeller has a concentric region directed axially upwards, - a second heat transfer medium return annular passage encloses the region of the pump housing that is directed upwards and is in flow connection with the inflow to the propeller via a multiplicity of pump housing openings, which are evenly distributed over the circumference of the pump housing, and - the outlet of the main heat exchanger is connected to the second heat transfer medium return annular passage.