Sufficient data exist to provide a high level of confidence that refractory-alloy-clad ceramic fuel pins and refractory structural alloys can be used successfully in an operational space power system. However, data are not yet sufficient to ensure that these materials can meet the temperature, lifetime, and system mass envelope requirements for reliable operation of a 100 kW(e) system as specified by the SP-100 Project. Development efforts to provide these data are being initiated.