[en] In the hot gas ducts of high temperature reactors high velocities (70< u<200 m/s) occur, as at the same time the primary circuit is pressurized (40< p<60 bar) the dynamic pressure forces have a high intensity. The aim of the present work is to measure the intensity of the fluctuating pressure generated in several differently shaped bends of the ducts according to its level and frequency. The dynamic pressure forces are caused by the velocity fluctuations of the flow (turbulent motion or flow separation phenomena). As it is well known flow separation occurs in bends and produces large eddies travelling downstream and generating pressure fluctuations. In the model tests four types of bends have been examined: circular bends of circular cross section (angle of deflection 90⁰ and 180⁰, curvature ration R/d=1,5, R/d=2,5 and R/d=5); 90⁰-bends of segmental design; 90⁰ bends, mitred; 90⁰-mitred, rectangular channel. For comparison the pressure fluctuations of the straight tube were also determined. The experiments were conducted in air, pressurized air and helium. The pressure fluctuations were measured by means of condenser microphones. The energy needed for the velocity fluctuations is taken from the flow in the form of a streamwise pressure loss, k being the fraction of the pressure drop necessary to supply the pressure fluctuations, the experiments have shown that k is constant for particular types of flow. For bends with small curvature ratios R/d, is k approximately 0.2. Flows with a pressure drop predominantly caused by friction are characterized by k approximately 1.0. These data hold for the ovrall rms-values of the pressure fluctuations. The experiments indicate that similar relationships also exist for discrete frequencies selected from the spectrum. The frequency spectrum is broad and exhibits no prevailing frequencies. The intensity of the pressure fluctuations considerably decreases in the frequency range 400< f<1000 Hz