The behavior of two nuclear materials, namely cubic zirconia and urania, is investigated under different irradiation conditions in the low and medium ion energy range (tens of keV to a few MeV). In each case, these materials display a multi-step damage build-up, as revealed by both RBS/C and XRD measurements. It is demonstrated that each step exhibits characteristic features such as damage fraction, elastic strain, nature of defects, and thus presents a specific microstructure. The transition from one step to the following involves radiation defect re-organization which arises to lower the energy of the system.