Future High Energy Physics experiments require sensors to operate at extreme fluences exceeding $1\times10^{17}$ 1 MeV n$_{eq}/$cm$^2$. Therefore, technologies used for the HL-LHC scenario will be no longer applicable and novel sensors and readout electronics must be devised. Within this framework, state-of-the-art Technology CAD tools can be proficiently used to account for the radiation-induced damage effects in semiconductor sensors, fostering design optimization and enabling predictive insight into the electrical behavior of novel solid-state detectors. Various numerical models addressing radiation damage effects have been developed and applied to the study of irradiated devices and will be illustrated in this work. Their applicability needs to be extended to extreme fluences accounting for the modeling of dopant removal, impact ionization, carriers’ mobility and lifetime, and trap dynamics.