Future sodium cooled fast reactors (SFRs) with Minor Actinide (MA) burning potential have to demonstrate an enhanced safety, minimal waste production and increased proliferation resistance in addition to their high economical potential. In this context, the PELGRIMM project, part of the European Framework Program 7 (FP7), investigates new MA-bearing oxide fuel developments for SFRs. Two fuel designs are studied: the standard pellet and the innovative sphere-pac fuel. Due to its favorable swelling behavior expected under irradiation and its dustless fabrication, the latter one appears to be a promising option. A special work package in PELGRIMM addresses the safety performance of this fuel under operational, design basis (DBC) and design extension conditions (DEC). For the preliminary safety assessment, the Working Horse (WH) core, designed and analyzed in the former CP-ESFR project was chosen. The SIMMER-III code was applied after implementing key features as the specific thermal conductivity of sphere-pac fuels. The feasibility of loading the core with MOX sphere-pac instead of pellet fuel, regarding operation and safety limitations, was first proven. Both fuel designs for the WH core at beginning of life and after irradiation were then compared at nominal and under unprotected loss of flow conditions. Results show a similar behavior of these fuels under irradiation, opening a perspective to the practical application of sphere-pac fuels in SFR systems. (C) 2015 The Authors. Published by Elsevier Ltd.