A design concept and supporting analysis are presented for a He-cooled fast reactor for the transmutation of spent nuclear fuel. Coated transuranic (TRU) fuel particles in a SiC matrix are used. The reactor operates subcritical (k 0.95), with a tokamak D-T fusion neutron source, to achieve >90% TRU burnup in repeated five-batch fuel cycles, fissions 1.1 tonnes/full-power year, and produces 700 MW(electric) net electrical power. The reactor design is based on nuclear, fuels, materials, and separations technologies being developed in the Generation-IV, Next Generation Nuclear Plant, and Advanced Fuel Cycle Initiative programs and similar international programs, and the fusion neutron source is based on the physics and technology supporting the ITER design.