The mechanical design of the primary system and associated equipment of MYRRHA is driven by two basic requirements.
1. Since MYRRHA is to be a flexible irradiation facility that can host irradiation rigs, the capability of easy and frequent fuel reshuffling and flexible core access for (un)loading the irradiation rigs are very desirable features.
2. The irradiation objective, in particular the demonstration of transmutation, requires a high fast neutron flux which in turn implies a compact core, with high thermal loading on the fuel. Such fast and high flux consequently mandates liquid metal cooling.
The spallation target module and the core are immersed in a pool of lead-bismuth eutectic (LBE) that serves as coolant for both the spallation target and core; it also serves as a reflector/shielding for the fast neutrons and gamma rays.
A pool-type design for MYRRHA has not only been chosen from a safety point of view but also to provide an extremely flexible core management.