A model of the IBR-2 pulsed reactor of periodic operation is developed to facilitate modeling of transitional processes. The model is constructed as a module structure with the help of discrete transitional functions of the kinetics, power feedback, and automatic regulator blocks taking into account nonlinear relationships. Good agreement between the calculated and experimental dependence of changes in the power for different changes in the setting reactivity is achieved. Using the model, power transition processes have been evaluated at different values of the parameters of the automatic power regulator (APR). It has been shown that the best transition processes correspond to higher APR rates at the elimination of the APR smoothing unit. Recommendations are given for choosing the APR parameters.