The dynamic analysis of the reactor internal structure in a typical pressurized-water reactor system, subjected to step, periodic, and seismic excitations, is presented. Employing the finite element approach of structural analysis, the governing differential equations describing the motion of the system are set up and integrated numerically in time. It is shown that the introduction of three types of structural elements, elastic, rigid and pin-joint members with nodes having three degrees of freedom, provides an adequate mathematical model for the solution of reactor structural dynamics problems. A main distinctive feature of this analysis is the application of “elements” global stiffness matrices in place of the standard structural global stiffness matrix. It is shown that this feature reduces the computer storage requirement and running time considerably. An examination of the system dynamic response characteristics indicates that when the clearance between the reactor internal components is relatively small, impact between various components could occur. The magnitude of the impact forces for periodic and seismic excitations is computed. Furthermore, a procedure for the calculation of the upper bound of integration time step is presented which ensures the numerical stability of the solution.