The deformed microstructures of irradiated F82H uniaxial tensile specimens have been examined following irradiation in the High Flux Reactor (HFR) to 2.6 dpa at 327°C in order to identify controlling mechanisms. Deformation following irradiation is found to occur in poorly defined channels, causing formation of discrete steps at surfaces, similar to that in unirradiated steel. Deformation is by motion of individual a/2 ⟨111⟩ dislocations.