The radionuclide fractionation process in fuel-like hot particles from the fallout after the Chernobyl accident is analyzed. Some processes which can be responsible for different kinds of fractionation of fission products in hot particles and nuclear fuel are suggested. These comprise: evaporation (Cs and Ru), thermal diffusion within fuel rods (visible mostly in Ce) and half-life effects, influencing the spatial dependence of relative content of isotopes of the same element (Ce and Ru). The analysis proves the local origin of hot particles, i.e. the absence of considerable mixing between fission products from different parts of the reactor in the process of hot particle formation.