SCKCEN, the Belgian Nuclear Research Centre, and IBA s. a., Ion Beam Applications, are developing jointly the MYRRHA project, a multipurpose neutron source for R&D applications related to the ADSR concept.

The design of MYRRHA needs to satisfy a number of specifications such as the following. [61]

‘{E > 0.75 MeV) = 1015 n/cm2/s at the locations for MA transmutation; ‘{E > 1MeV) = 1013 to 1014n/cm2/s at the locations for structural material and fuel irradiation;

‘{Eth) =2 x 1015 to 3 x 1015 n/cm2/s at locations for long-lived fission product (LLFP) transmutation or radioisotope production.

• Subcritical core total power, ranging between 20 and 30 MW.

• keff < 0.95 in all conditions, as in a fuel storage, to guarantee inherent safety.

• Operation of the fuel under safe conditions: average fuel pin linear power <500 W/cm.

In its present state of development, the MYRRHA project is based on the coupling of an upgraded commercial proton cyclotron with a liquid Pb-Bi windowless spallation target, surrounded by a subcritical neutron multiplying medium in a pool type configuration. The spallation target circuit is fully separated from the core coolant as a result of the windowless design presently favoured in order to utilize low-energy protons without reducing drastically the core performances. The core pool contains a fast — spectrum core, cooled with liquid Pb-Bi, and several islands housing thermal spectrum regions at the periphery of the fast core. The fast core is fuelled with typical fast-reactor fuel pins. The central position is left free to house the spallation module. The proton beam will be impinging on a molten lead or tungsten target.

The accelerator parameters presently considered are 5 mA current at 350 MeV proton energy. The positive ion acceleration technology is envisaged, resting on a two-stage accelerator, with a first cyclotron as injector accelerating protons up to 40 to 70 MeV and a booster further accelerating them up to 350 MeV.