[en] The results of calculational-experimental study of the effect of fuel element dry lattice on critical size (height) and reactivity of uranium-water critical assemblies are considered. The experimental and calculational techniques are briefly described. The study is conducted in the framework of the research program on studying the physics of the ABV type small-size water cooled and moderated reactors. The experiments have been made on the MATR-2 critical benchmark with assemblies which consisted of either WWER type fuel rods with uranium dioxide of 5% enrichment or annular fuel elements with fuel composition on the base of uranium-aluminium alloy with enrichment of 36% ₂₃₅U. The calculations have been performed according to the technique based on the two-group diffusion approximation. The dependences of assembly critical height change on dry lattice thickness for different fuel element lattice pitch are obtained. The conclusion is made that calculational results are in good agreement with the experimental data. Thus the divergence in calculational and experimental absolute values of critical heights and differential reactivity for uranium-water assemblies can not be totally associated with errors in fuel element dry lattice calculation