The production of small, coherent BCC precipitates of copper during fast neutron irradiation of ferritic steels and their apparent stability at peak hardening size are important phenomena governing in-service irradiation embrittlement. An MD model employing manybody interatomic potentials for the Fe-Cu alloy system has been developed and used to simulate the effect of displacement cascades on both dilute random solid solutions of copper and small coherent BCC copper precipitates in an oa-iron matrix. Within the timescales that can be modelled, cascades caused only small changes to the distribution of copper atoms in both the solid solution and the precipitate studies. Vacancies are observed to bind to copper solute atoms and also to accumulate in precipitates near the interface, where they are mobile. Interstitials are mobile in the solid solution matrix and two mechanisms of interstitial entrapment by precipitates are indicated.