This paper presents a mixed-binary linear programming formulation to solve the problem of radial distribution systems expansion planning. The proposed model considers the alternatives of repowering existing substations, allocation and sizing of new substations, reconductoring of existing feeders, construction and type selection of new feeders and changes in the system topology. The use of a mixed-binary linear model guarantees convergence to optimality using existing optimization software. In the proposed model, the steady-state operation of radial distribution systems is modelled through linear expressions. Two test systems found in the literature were used to show the efficiency of the proposed method.