NUBOW-3D is a special purpose structural analysis code to analyze core deformations using detailed mechanical analyses in support of design of core restraint systems. The code models the core in 3-D space using 1-D beam elements and determines the transverse displacements of the beam (axial displacement is not included). The code accounts for a core restraint system as part of the boundary conditions. Inelastic effects of irradiation creep and swelling are included as is duct-to-duct contact. The code requires thermal power and flux fluence information as input obtained from DIF3D calculations. NUBOW-3D calculates the displacement response over time for specified power to flow ratios. If reactivity displacement worths are available, NUBOW-3D can estimate the reactivity worth of spatial deformation as a post-processing step.