SUMMARYOne design concept for a gas cooled fast reactor fuel element utilizes directly cooled coated fuel particles. The fission product retention barrier is a pyrolytic SiC layer approximately 50 μm thick and 1 mm diameter. Knowledge of the structure of this material and its irradiation performance after high neutron doses is vital to the success of such reactors.Specimens oriented both parallel and perpendicular to the radius can be prepared from the shells by ion beam sputtering. The defect structure and preferred orientation of the coatings is being investigated. The high voltage electron beam is being utilized to measure the atomic displacement energy and to simulate fast neutron damage at temperatures relevant to reactor conditions