The formation of ‘cleared’ channels in neutron irradiated metals and alloys have been frequently reported for more than 40 years. So far, however, no unambiguous and conclusive evidence showing as to how and where these channels are initiated has emerged. In the following we present experimental results illustrating initiation and propagation of channels during post-irradiation deformation of neutron irradiated copper and a copper alloy. The observations strongly suggest that the channels are initiated at boundaries, large inclusions and even at previously formed cleared channels. Some of the channels have been observed to penetrate through both the twin boundaries and grain boundaries. It is argued that the high stress level reached during post-irradiation tensile tests activate dislocation sources at the sites of stress concentrations at boundaries and interfaces. The propagation of these newly generated dislocations in the matrix causes the formation of cleared channels. Implications of these results are discussed with specific reference to the origin and consequences of plastic flow localization.