The process to bring a new fuel type to implementation requires a phased approach:
When analysing the technical readiness level of MYRRHA driver fuel after the screening research conducted in the period 2000-2008, one can state that the screening phase is practically completed and advancements are now made in the pre-qualification phase. The fuel qualification programme is still under development, and the demonstration phase should be performed in the reactor itself, taking into account innovative coolant and cladding.
Mixed plutonium-uranium OXide fuel (MOX) was selected as the main candidate already at the beginning of the MYRRHA project, taking into account a large experience in the MOX production in Europe and its better neutronic properties in a fast neutron spectrum than uranium dioxide. Aiming at a compact core with high neutron flux, an enrichment of 30-35 wt. % of reactor grade (RG) Pu has been preliminary chosen.
Regarding property measurements and ex-pile tests, the research programmes of the past century are sufficiently well conducted for the stand-alone fuel properties, exploration work concerning the interaction between the steel claddings and LBE coolant were conducted in the framework of EURATOM coordinated projects. Irradiation tests of the selected cladding materials under representative temperature, coolant and spectrum conditions have still to be done.
The first candidate material for MYRRHA fuel cladding is T91 FMS on long-term, but for the first core load fuel elements with claddings made of one of 15-15 Ti class austenitic steels (ASS: e.g. AIM1) are envisaged with lower limit for the cladding damage.