Application of virtual fitting in the manufacturing of the ITER European vacuum vessel sectors

Abstract

The Vacuum Vessel is one of the main systems of the ITER tokamak. The welded steel, torus-shaped vessel, houses the plasma and acts as a first safety containment barrier. It provides support for In-Vessel components and removes the heat generated during operation by mean of cooling water circulating through its walls. To ensure the functionality of the system, strict geometrical requirements have been defined on several features. The large scale of the component and the complexity of the manufacturing raised the need to develop metrology strategies that improve the awareness of the decision-making processes and minimize the risk of non-compliance of the final product. Virtual Fitting is a technique that enables to find the optimal way of assembling parts together considering their real shapes. By defining requirements to include in the analysis and their priority, an optimum can be found by least square minimization of the as-built data deviation from the nominal reference. The method has been deployed in one of the most critical stages of the Vacuum Vessel production, the assembly of the four poloidal segments composing the final sector. The analysis provided the actors involved several alignment scenarios, from which corrective actions have been derived, in terms of time, cost and quality. Firstly, this paper presents the principles of the Virtual Fitting technique, then the second part focuses on the application of the Vacuum Vessel European Sector #5.