[en] An adequate model of dynamic behaviour of fuel rods in NPP-s was generated to estimate their eigenfrequencies. The eigenfrequencies were computed for different kind of clamps of the rods. Contrary to the usual models based on string vibration this model showed that the eigenfrequencies took place at the quadratic higher harmonics. These solutions agree with the earlier results of measurements. Changes in the eigenfrequencies of lower models were detected and interpreted by the examination of different clamping modes. (author) 6 refs.; 8 figs