The TRIGA Mark II Reactor of the Atominstitut Vienna went critical for the first time at 7.3.1962. Within the framework of the “global threat reduction initiative (GTRI)”, all fuel elements (several of them high enriched) were shipped back to Idaho Falls, US in 2012. In return, slightly used and low enriched fuel elements were delivered from US to the Institute. Subsequently, between 2015 and 2017 the Instrumentation & Control System (I&C) and reactor related components including the primary, secondary and purification circuits (heat exchanger, ion exchanger), the ventilation system and other auxiliary systems (crane, cables, lightning, power supply (also UPS)) were replaced. In addition, the security system and radiation protection system were also renewed. The presentation will describe the renewal process including technical challenges.