In order to perform safety oriented transient analyses, the entire nuclear power plant has to be simulated in most cases. However, a high level of resolution is only needed where the safety parameters may reach the safety criteria. In this paper, three scale resolutions are defined (NPP level, core level, fuel pin level). Thermal-hydraulic and neutron kinetic codes are already available for each scale. By coupling them, it is possible to develop a complete simulation tool giving access to the required level of precision at each scale level. For this purpose the Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) mbH has developed a number of coupled thermal-hydraulics/neutron-kinetics code systems which can solve the defined goal on assembly-wise or pin-by-pin level. Three types of couplings are applied depending on the utilized codes and application purposes: internal, external and parallel. An overview of the existing and future coupled systems available at GRS is given in this paper.