Irradiation effects on the optical and mechanical performance of ITER prototype window assemblies

Highlights: ► Assessment of the diagnostics windows assembly technologies under ITER relevant conditions. ► Reactor irradiation of prototype ITER-compatible window assemblies up to up to a total fast (E > 0.1 MeV) fluence of ∼2 × 1020 n/m2. ► Vacuum leak testing at normal and elevated temperatures before and following reactor irradiation. ► Push-out mechanical testing including the final destructive test. -- Abstract: We investigated how simulated ITER environment can influence the mechanical stability and optical characteristics of ITER prototype window assemblies. Such assemblies must transmit diagnostic signals while maintaining the vacuum boundaries continuously during the operating life of ITER. A high reliability of the window assemblies is a must. Prototype assemblies with the transmission element made of Si3N4, silica, or sapphire diffusion bonded or brazed to a stainless steel or Ti ferrule were studied in the present work. Irradiation was performed in the BR1 reactor of SCK•CEN in Mol at 150 °C during 5.5 months up to a total fast fluence of ∼2 × 1020 n/m2. Post-irradiation thermo-mechanical and the He-leak tests were performed in a hot cell. The examination was concluded with the destructive push-out test. Different damage patterns were observed for different window assemblies. The general conclusion is that after thermal cycling and reactor irradiation the windows remain sufficiently strong to sustain mechanical loads relevant for the ITER operation