The replacement of the internal plasma-facing components (first-wall and blanket segments) for maintenance or at the end of their lifetime is an important aspect of the design of the Next European Torus (NET) and of the remote handling procedures. The first phase of development of the design software tool INVDYN (inverse dynamics) is presented, which will allow optimization of the movements of the internal segments during replacement, taking into account inertial effects and structural deformations. A first analysis of the removal of one NET internal segment provides, for a defined trajectory, the required generalized forces that must be applied on the crane system.