A design for a palladium diffuser and fuel cleanup system for a deuterium-tritium fusion reactor is proposed. The feasibility of the palladium-alloy membrane method is discussed based on early studies by the authors. Operating conditions of the palladium diffuser are determined experimentally. Dimensions of the diffuser are estimated from computer simulation. A fuel cleanup system is designed under the feed conditions of the Tritium Systems Test Assembly at Los Alamos National Laboratory. The system is composed of palladium diffusers, catalytic oxidizer, freezer, and zinc beds and has some advantages in system layout and operation. This design can readily be extended to other conditions of plasma exhaust gases.