The 'complete' neutronic characterisation of the FASTEF critical core by ERANOS/JEFF3.1. Some proposals for Task 2.2: a possible approach for the sub-critical mode.

This work was carried out in the CDT/FASTEF EU FP7 project: it deals with the preliminary core design of MYRRHA-FASTEF, a 100 MW LBE cooled reactor (working in both criticai and sub-critical modes) that should be able to demonstrate transmutation and associated technology. The report summarizes the 'complete' neutronic characterisation of the 100 MW FASTEF critical core, presented at the CDT/WP2 meeting on June 23-27 2011 at the SCK-CEN research centre of Mol (B). It is divided in three main sections. In the first part, the reference core layout (defined in CDT-REP007-2011, ENEA Technical Report UTFISSM-P9P0-011, June 2011), was analysed by means of the ERANOS 2.1 deterministic code, by adopting the JEFF3.1 nuclear data library and a 51-energy-group structure. The neutronic results, referring to the BoL/BoC/EoC conditions, deal mainly with power/flux distributions, peaking factors, anti-reactivity requirements and performances of shutdown systems. Such results will be used as a basis for TH and TM characterisations in the CDT/FASTEF project. In the second part, the main reactivity coefficients related to thermal effects were investigated at different time steps of the fuel cycle by means of a 33-energy-group structure. Other important safety features were evaluated, as: the delayed neutron fraction, the void and core compaction effects. Such results will be used as a basis for the safety analyses in the CDT/FASTEF project. Finally, in the third part, a possible approach for the design of the sub-critical core layout is introduced.