In this work, dynamic responses of a WWER-1000 reactor in reactivity insertions are studied using a coupling method. The ANSYS-CFX is implemented for thermal hydraulic study of the core and the point kinetic equation (PKE) is coupled as a FORTRAN subroutine. For transient analysis of the core, the thermal feedback of the fuel is added to coolant, and numerical solver of cylindrical heat transfer for obtaining the irradiated fuel rod temperature profile is also included. In order to investigate the irradiation effect, the fuel and gap properties in burnup with appropriate correlations could be calculated. Using memory management system (MMS) and data transfer arrays, coupling between numerical subroutines is carried out. It is shown that the dynamic response of the core depends on burnup, and the response could be varied in time. In addition, the coupling method is reliable for other dynamic calculations.