•A simplified model of the ITER Vacuum Vessel has been created for dynamic analyses.•The simplified model is based on a novel substructuring method.•Creating a model by combining many small superelements speeds up calculations.•The dynamic fidelity of the simplified model is excellent. In order to characterize the behaviour of the ITER Tokamak during seismic events, it is desirable to integrate Finite Element (FE) models of the Tokamak into the model of the building (Tokamak complex). Detailed FE models exist for each of the main Tokamak systems, but these are so large that combining them is computationally impractical. The aim of this paper is to present work performed on the creation of simplified models of the ITER Vacuum Vessel (VV) for use in global seismic analyses. Two different methodologies have been considered for creating simplified models whose dynamic behaviour matches that of a detailed benchmark model. In the first method, a coarse mesh representing the shape of the VV is created. The element properties of this mesh are then modified using optimization algorithms until the desired dynamic behaviour is achieved. The second method makes use of substructuring. In order to minimize the wavefront (and hence computational time), the simplified model is created from multiple superelements, each representing part of the VV. The suitability of the simplified model based on substructuring is quantified by means of the Modal Assurance Criterion (MAC) and Power Spectrum Density (PSD) analysis.