Structural analysis of the Interspace Afocal Module of the Wide Angle Viewing System diagnostic for ITER

•Structural Integrity of the Preliminary Design of the ITER Interspace Afocal Module (IAM) is ensured for every Load combination.•IAM Natural frequencies are validated.•Optical performance of IAM is guaranteed in Operating Conditions.•Optical errors in the IAM due to thermo-mechanical deformations are analysed. The Interspace Afocal Module (IAM) is one integral component of the ITER Visible/Infrared Wide Angle Viewing System (WAVS), which is an optical diagnostic aimed at monitoring the ITER plasma facing components for machine protection. The diagnostic comprises 15 lines of sight (LoS), strategically distributed in the ITER Equatorial Ports (EP) 3, 9, 12 and 17. Design of WAVS in EP12 is critical, since it has to be fully operational for the first plasma of ITER; it is at its Preliminary stage, carried out by the Consortium constituted by CEA, CIEMAT and Bertin Technologies, within the Framework Partnership Agreement financed by F4E. The WAVS in EP12 comprises three LoS that pass through the IAM, consisting in a refractive optical system that relays the pupil forward and controls the beam diameter. It includes two doublets of lenses for each LoS, made of Shappire and Calcium Fluoride, with diameters up to 128 mm. The afocal sets (up to 1.9 m in length) are tightly held in place by the support structure of the IAM, which is directly attached to the Interspace Support Structure (ISS). The IAM structural requirements are highly demanding, given the optical performance that has to be assured under thermal and inertial loads in normal operation, including seismic SL1. In addition, it also has to withstand loads in Category III and IV, including higher seismic events SMHV and SL2, or accidental loads such as the loss of coolant or fire events, since the IAM structure is classified as ITER Safety Relevant, due to its attachment to the ISS. The paper summarizes the structural analyses performed by CIEMAT to validate the mechanical behaviour of the IAM Preliminary design in EP12, to guarantee both the structural integrity and the optical performance, in accordance with the RCC-MR Code.