[en] This paper analyses the effects of uncertainties in the modulus of elasticity of the constructional material, soil stiffness and the mass of structure on models corresponding to two typical structures in the Paks Nuclear Power Plant. The structure has been modelled as a beam model, and in computation of soil springs, a stiff foundation has been taken into account. Analyses show that masses must be taken into account as correctly as possible, but the effects of soil stiffness are sharply different with flexible and rigid structures. This effect in the case of flexible buildings is less important than in the case of rigid-box-like structures. (author)