A methodology for homogenization and functionalization of one-dimensional cross sections for RETRAN has been developed and encoded into the SIMULATES and SLICK computer programs. The method relies on the SIMULATE-3 nodal reactor analysis code to provide accurate solutions of the three-dimensional neutron diffusion equation in two energy groups. The process of producing the required data involves two distinct problems: (a) the spatial homogenization of the three-dimensional cross sections and diffusion coefficients into one-dimensional variables and (b) the functionalization of the one-dimensional data in terms of the feedback variables of coolant density, fuel temperature, and control fraction. The homogenization method is based on equivalence theory and preserves the eigenvalue and one-dimensional planar reaction rates of the three-dimensional solution. The functionalization of the homogenized cross sections is accomplished by performing analogous one-dimensional state calculations with the RETRAN thermal-hydraulic models and then fitting to the RETRAN feedback variables. The methodology has been verified by comparing the results of one-dimensional calculations performed with the one-dimensional cross sections to three-dimensional calculations. Close agreement between the one- and three-dimensional results has been demonstrated.