Since 1998, SCK center dot CEN, in partnership with IBA s.a. and many European research laboratories, is designing a multipurpose Accelerator Driven System (ADS) - MYRRHA - and is conducting an associated R&D support programme. MYRRHA aims to serve as a basis for the European experimental ADS to provide protons and neutrons for various R&D applications. Besides an overall configuration of the MYRRHA reactor internals, the description in this paper is limited to the mechanical design of the main components of the Primary System and Associated Equipment (vessel and cover, diaphragm, spallation loop, sub-critical core, primary cooling system, emergency cooling system, in-vessel fuel storage and fuel transfer machine), the conceptual design of the robotics for In-Service Inspection and Repair (ISIR), together with the remote handling for operation and maintenance (O&M). (c) 2006 Elsevier Ltd. All rights reserved.