The need for a new steady-state fast-neutron reactor has been the subject of numerous national meetings and discussions. This type of reactor will be able to open new frontiers of research for Generation IV reactors, the Space Propulsion Program, and the Advanced Fuel Cycle Initiative. With the confluence of these three programs' fast-spectrum testing needs, we set out to conceptualize a new system by looking at previous successful reactor concepts. This paper presents a new concept for a fast-spectrum test reactor that is horizontal in orientation, with individual pressure tubes running the entire length of the scattering-medium tank filled with a liquid heavy metal. This approach for a test reactor will provide more flexibility in refueling, sample removal, and ability to completely reconfigure the core to meet different users' requirements. Full core neutronic analysis of more than 14 combinations showed that a large hexagonal steam-cooled U-10Zr fuel, with a core power of 267 MW(thermal), produced a fast flux (>0.1 MeV) of 1.3 × 1015 n/cm2s averaged over the whole length of the irradiation channel. A depletion run with an initial enrichment of 20 wt% 235U had a flat reactivity curve for the first 180 days of cycle due to in-core breeding. Although considerable neutronic optimization and a thermal-hydraulic analysis remain to be performed, it appears that a reactor core with this innovative geometry could meet future fast flux testing needs.