[en] For most of its length an accelerator for breeding nuclear fuel will consist of a series of heavily beam-loaded accelerating structures operating at energy gradients around 1 MeV/m. In this report the design of a structure with on-axis couplers is described. It has certain advantages over the disk-and-washer structure and its suitability for use in the high energy end of such an accelerator will be studied with a continuous 50 mA electron beam at an injection energy of 1.5 MeV. Low power rf tests show that a first-neighbour coupling coefficient up to 11% is possible. The structure is easy to manufacture. A newly discovered structure property may lead to simple tuning procedures. (author)