Isotopically-modified materials, in which the isotope content of chemical elements is different from natural values, have found wide application in various fields of the economy (nuclear power engineering, medicine, fundamental research, etc.). The composition of isotope mixtures changes in a separation process. The growing demand for isotopically-modified materials has resulted in an amount of research aiming to improve the technology of isotope mixture separation. One of the main negative factors decreasing the effectiveness of the MCIM separation process is nonstationary hydraulic and separation processes in gas centrifuge (GC) cascade. The research into the effects of nonstationary processes on the efficiency of MCIM separation seems to become even more important. An experimental approach in this case appears to be quite costly, so it is strongly recommended that nonstationary processes should be investigated by mathematical modeling.