A nuclear reactor core includes a plurality of core assemblies. The core assemblies have a cooperating structure formed at one or more load pads that mechanically couple the plurality of core assemblies together to limit relative motion between core assemblies in a kinematically determinate way. A shear key on one core assembly is configured to fit in a tab slot on an adjacent core assembly. Motion of one core assembly is transferred to a second core assembly and the core assemblies move together.