To consider the inter-relation of various components of a tokamak reactor in a self-consistent manner, a system analysis code is coupled with a one-dimensional radiation transport code, ANISN, which provides the neutronic response for reactor components. By using the coupled system analysis code, the operational space for a low aspect ratio (LAR) tokamak reactor with a superconducting toroidal field (TF) coil is investigated with an aspect ratio in the range of 1.5-2.5. The minimum major radius which satisfies all the physics and engineering requirements increases with the magnetic field at the magnetic axis. A required inboard shield thickness is mainly determined by the requirement on the protection of the IF coil against radiation damage. It is shown that the minimum major radius increases as the magnetic field increases and higher magnetic field is required to have a same fusion power in higher aspect ratio cases. (C) 2010 Elsevier B.V. All rights reserved.