Three Dimensional Tolerance Investigations on Assembly of ITER Vacuum Vessel

The ITER machine will consist of many large and complex components that shall be produced by various manufacturers located around the world. The Vacuum Vessel has to be fabricated as 9 toroidal sectors, each spanning 40 degrees and including some port structures. Sectors and other port structures are connected to each other at the ITER site to form the completed Vacuum Vessel torus. To ensure that the machine assembly can achieve the geometric design specification, it has been necessary to analyse and develop key functional tolerances for a wide range of interfacing components. By modelling the full assembly process with respect to size and position, the potential variances of the component parts and their contribution to the finished assembly have been quantified. The process tolerances are determined by stacking up a series of key singular tolerance in a controlled statistical manner. These include tolerances associated with the manufacturing process, assembly positioning capability and weld shrinkage. From the integration point of view, all key interface tolerances have to be analyzed and the results presented and documented in a complete and consistent manner. In order to meet the complexity of this task a special tolerance calculation and simulation programme, provided by the US Company Dimensional Control Systems (DCS), was chosen. As one of the core ITER components, the assembly tolerance study was initiated on the Vacuum Vessel. The results of these investigations are to be considered as a baseline for all other vessel and in-vessel components such as Thermal shield, Port plugs, Divertor, Blankets, ELM coils etc. Manufacturing tolerances of VV sectors were provided as input data for this study. Then assembly tolerances (positioning capability in 3D, weld shrinkage variation estimates) were applied on the 3 dimensional model of the VV.