This work has been carried out in the framework of the CDT/FASTEF EU FP7 project: it deals wfth the preliminary FA/core design for MYRRHA-FASTEF, a 100 MW LBE cooled reactar (working in both critical and sub-critical modes) that should be able Io demonstrate transmutation and associated technology. This analysis is focused on the critical option, even if the main features af the sub-critical one (having the same FA structure) have to be foreseen since the beginning. The FA exploits the usual SFR architecture, with the pin of the Phenix French reactar and an enlarged wire diameter, in order to 'fit' the room needed by the spallation target (FA pitch = 104.5 mm) and, at the same time, by obtaining same benefits for the core cooling and pressure Iosses. The two shutdown systems (3 LoD) satisfy the guess (but reasonable) safety criteria assumed. The secand part of the presentatian (done at the WP2 meeting, on 23-23 June 2010 in Mol, Belgium) defines same details af the work plan far the WP2 - Task 2,2 (in which ENEA is responsible).