[en] The experimental results of studies of local temperature changes in simulative assemblies of the BN-350 and BN-600 fast reactors are presented, when displacing central and peripherical (side and angular) fuel elements on a half of a gap between fuel elements under non-unuform heat load conditions. Displacement of fuel elements (cassette with ribbed fuel elements and displacers) leads to the increase of side fuel elements temperature non-uniformity 1.5-2 times as compared with the nominal variant. The effect is even more considerable (approximately 6 times) for the system of smooth fuel elements. Maximal temperature non-uniformities of central, side and angular fuel elements at their displacement are estimated using the experimental formulas obtained. The generalized formula based on the experimental data for nominal geometry with introduction of the lattice deformation correction factor is recomended for side fuel elements. It is shown that increase of separate fuel element power by 50-100% is not dangerous for their operation due to scattering of temperature spot at the expense of intensive interchannel exchange and sodium high thermal conductivity