MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is the flexible experimental accelerator-driven system (ADS) in development at SCK*CEN. MYRRHA is able to work both in subcritical (ADS) and in critical mode. In this way, MYRRHA targets the following applications catalogue:

• To demonstrate the ADS full concept by coupling the three components (accel­erator, spallation target, and subcritical reactor) at reasonable power level (50­100 MWth) to allow operation feedback, scalable to an industrial demonstrator;

• To allow the study of the efficient technological transmutation of high-level nuclear waste, in particular, minor actinides that would require high fast flux intensity ^>0.75MeV = 1015 n/cm2 s);

• To be operated as a flexible fast-spectrum irradiation facility allowing for

— Fuel developments for innovative reactor systems, which need irradiation rigs with a representative flux spectrum, a representative irradiation temperature, and high total flux levels (0tot = 5 • 1014 to 1015 n/cm2 s); the main target will be fast-spectrum GEN IV systems, which require fast-spectrum conditions;

— Material developments for GEN IV systems, which need large irradiation volumes with high uniform fast flux level (Ф>1 MeV = 1~5-1014 n/cm2 s) in various irradiation positions, representative irradiation temperature, and rep­resentative neutron spectrum conditions; the main target will be fast- spectrum GEN IV systems;

— Material developments for fusion reactors, which need also large irradiation volumes with high constant fast flux level (Ф>і MeV = 1 ~ 5 • 1014 n/cm2 s), a representative irradiation temperature, and a representative ratio appm He/dpa(Fe) = 10;

— Radioisotope production for medical and industrial applications by

• Holding a backup role for classical medical radioisotopes;

• Focusing on R&D and production of radioisotopes requiring very high thermal flux levels (Ф^ит^ = 2 to 3-1015 n/cm2 s) because of double­capture reactions;

— Industrial applications, such as Si-doping, need a thermal flux level depending on the desired irradiation time: for a flux level Ф^ит^ = 1013 n/ cm2 s, an irradiation time in the order of days is needed, and for a flux level of

thermai = 1014 n/cm2 s, an irradiation time in the order of hours is needed to obtain the required specifications.

Further in this section, we discuss some basic characteristics of the accelerator and of the core and primary system design.