Preliminary FA/core design for MYRRHA/FASTEF

This work has been carried out in the framework of the CDT/FASTEF EU FP7 project: it deals with the preliminary FA/core design for MYRRHA-FASTEF, a 100 MW LBE cooled reactor (working in both critical and sub-critical modes) that should be able to demonstrate transmutation and associated technology. This report is focused on the critical option, even if the main features of the sub-critical one (having the same FA structure) have to be foreseen from the beginning. The core design exploits the usual FA architecture of SFR with helical wire spacers. Since the use of LBE as coolant represents a 'huge' challenging issue, same specifications concerning the FA structure (as the enlarged wire) are to be intended as guess (but reasonable) values. This is caused by the uncertainties related to some parameters, having a strong impact an thermo-mechanical and thermal-hydraulic core features, as: the pin-bundle stability during irradiation, corrosion/erosion effects, pressure Iosses and bowing in the presence of higher flux/power gradients. In spite of these uncertainties, the present work sketches some possible Iayouts of the (68 FA) critical core compatible with the cover plug design (that yields a high flexibility to the facility). Afterwards it identifies the most conservative Iayout for the irradiation facility (in terms of needed MOX Pu content) and shows its main neutronic performances evaluated at BoL by the ERANOS 2.1 deterministic code. Since there is the necessity to proceed with the core design, presumably the sketches here defined will be used as a basis for the deep characterisation foreseen in the WP2 - T2.2. But we are conscious that all the FA/core specifications could be frozen only by detailed analyses (T/H, CFD, thermo-mechanical studies with suitable codes) and using, as much as possible, the valuable experience gained with SFR.