A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprises fissile material contained in a containing structure and disposed in the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core. The upper internals include at least guide frames and internal control rod drive mechanisms (CRDMs) with CRDM motors mounted on a suspended support assembly including a plurality of hanger plates connected by tie rods. The plurality of hanger plates includes a lowermost hanger plate having alignment features configured to align the upper internals with the containing structure that contains the nuclear reactor core.