Civil and structural design for MYRRHA

MYRRHA, a Multi-purpose Hybrid Research Reactor for High-tech Applications, con-ceived as an Accelerator Driven System (ADS), is under development at the Belgian Nucle-ar Research Centre (SCK CEN). The project was approved by the Belgian government in 2018, releasing the funding for a first phase of staged implementation and operation. MI-NERVA, the implementation of phase 1 of MYRRHA, covers the design, construction and commissioning of the first Linear Accelerator (LINAC) section up to 100 MeV. Phase 1 also comprises pre-licensing towards the MYRRHA sub critical reactor driven by a 600 MeV pro-ton beam.
The MYRRHA Reactor is envisaged to be founded 27m underground, predominantly in permeable sands, with some clay layers and lenses and a near surface ground water level. The soft soil and deep bedrock proved to be a significant design challenge, and an for the nuclear industry innovative design of the civil infrastructure was utilized to satisfy the leak-tight containment requirements for the primary system and to prevent ingress of ground wa-ter and flooding. Another technical challenge, requiring specific analytical and design pro-visions, was the interface of the reactor with the 600 MeV proton beam and its alignment. There, strict design constraints on vibration transmissions and differential settlements were set for normal operation conditions. At this interface, as well as locations housing critical safety systems, the challenge was also driven by the structure’s response to design basis and design extension events, especially the seismic and aircraft impact scenarios. A proper Soil Structure Interaction was performed, considering the effect of embedded foundation and potential ground improvement.