A statistical study on as-built deviation of ITER blanket shield block interfaces

Abstract

The blanket shield block (SB) is a key component of ITER blanket system, providing critical interfaces for the attachment of the first wall (FW) and assembly within the vacuum vessel (VV). To ensure assembly feasibility which is first assembled on VV in ITER site, the SBs are manufactured with a dimensional (size) tolerance of ±1 mm on the external surfaces, while critical features directly interfacing with mating components require position of 0.2 mm, and flatness of 0.02 mm specified using Geometrical Dimensioning and Tolerancing (GD&T). In addition, key components of ITER are manufactured by multiple domestic agencies (DAs) and procured independently, accurate as-built dimensional information is essential for assembly preparation. In this study, dimensional (size) tolerance and geometrical tolerances of 54 inboard SBs manufactured in KODA were statistically analyzed against the applied size and GD&T requirements using descriptive statistics, considering measurement uncertainties associated with three-dimensional coordinate measuring machines (3D-CMMs). Based on the statistical analysis using normalization of manufacturing deviation and process capability index with centering, key interfaces area of SBs requiring process improvement were identified. These results provide quantitative insight into SB manufacturing accuracy and support the prevention and diagnosis of potential integration issues during ITER tokamak assembly. In addition, the resulting as-built dimensional database could support on-site assembly by providing accurate geometric information to facilitate local fit-up or minor machining of the SB and mating components.