Nuclear fusion reactor-core components will undergo degradation of thermal and mechanical properties due to the combined effect of neutron irradiation and contact with plasma. This limits their operational lifetime and poses requirements for safe/efficient exploitation, calling for a quantification of the ageing of these structures. In support of the relevant safety evaluation, continuous progress in physical understanding of radiation damage phenomena and in computer science allows the development of multi-scale numerical tools to model the effects of irradiation on the mechanical properties of materials. The approach begins with the study of the production of atomic-scale defects in individual displacement cascades, initiated by neutrons, and ends with the application of plasticity and fracture mechanics, wherein the response of the material to changes in temperature and/or applied stress is of concern. Methods for modelling dislocations at the atomic and mesoscopic levels lie between these extremes. Mesoscopic models are known as dislocation dynamics (DD): they treat dislocations as strings governed by elasticity and local laws, thereby linking discrete defect behaviour to fracture mechanism models. Local laws (dislocation mobility and reactions with radiation defects) are to be provided by atomic-scale molecular dynamics (MD) simulations.