In order to develop predictive models of the mechanical response of irradiated materials it is necessary to understand the fundamental physical processes controlling the deformation. This is particularly important near yielding where local defect interactions may dominate the behaviour. Dislocation-defect interactions in copper containing various densities and distributions of stacking-fault tetrahedra and small dislocation loops were examined dynamically using the in-situ TEM straining technique. Defect annihilation mechanisms as well as the conditions required to produce defect-free channels are proposed. The experimental results are compared to atomistic simulations and continuum mechanics calculations of unit interactions. Based on these observations, an improved continuum model of the mechanical behaviour of irradiated materials is presented.