[en] The relationships between the most significant factors influencing the dynamic reactivity changes during the refueling are considered. The effect of all these factors is considered, as well as their changing during the refueling. A system of differential equations is derived for calculating the change of ¹³⁵Xe concentration and reactivity losses. The effect of isotope ratio changing during the refueling on the xenon poisoning is expressed in changing of the average neutron flux density, thermal neutron utilization factor, probability of obtaining ¹³⁵I and ¹³⁵Xe as fission products. Curves of dynamic poisoning in the beginning and the end of the first refueling campaign are shown. A software using files with preliminary calculated concentrations has been created for calculating poisoning dynamics computing. The program package can be used as a part of a training program for reactor operators and as a part of an information system for the personnel support. 2 figs, 5 refs