To determine the radial build of tokamak reactor systems, a one-dimensional radiation transport code is coupled with the system analysis. Neutronic effects such as the tritium breeding capability and the shielding characteristics are self-consistently calculated in the system analysis which allows a determination of the design parameters of a reactor which satisfy plasma physics and engineering constraints simultaneously. We apply this coupled analysis to determine the radial build of tokamak reactor systems and show that it is a powerful tool for the optimal design of a tokamak reactor.