The mixed-oxide (MOX) fuel of the current generation (MIMAS) is confronted with the challenge of reaching the same quality and reliability as UO2 fuel, while the related data base accumulated so far is still limited. Its in-reactor behavior, therefore, has been assessed based on the lessons from previous generations of MOX fuel. Results are presented for attributes specific to the MOX nature of the fuel, irrespective of the specific fuel design features. The results obtained progressively with MIMAS fuel confirm the adequacy of such an assessment.