The main problem we have to face in order to improve the in-pile behaviour of the UMo/Al dispersed fuel, is the instability of the interaction zone, that is formed between the UMo particles and their surrounding Al matrix during irradiation. As the latest irradiations (e.g. IRIS 3 or RERTR 6) tend to prove, addition of Si into the Al matrix seems to be beneficial for the interaction rate decrease. To further understand the role of silicon, a wide out-of-pile interdiffusion study has been launched in CEA-France in 2006 and is still under progress. It has given promising preliminary results by showing a real effect of Si addition upon the interaction zone. The first results related to the physico-chemical aspects of the modified UMo/Al interaction as well as the kinetics aspects of the interaction layer (IL) formation are described in this paper. On a wide range of annealed couples made of UMo7 or UMo10 and Al-Si matrix (Si content ranging from 0.11 wt % to 12 wt %), the IL thicknesses have been systematically measured. Microstructures have been fully characterized by means of optical and scanning electron microscopy and the elementary compositions have been evaluated through EDX analyses. Finally, XRD characterizations and micro-hardness tests have also been performed on a few samples. On the basis of these different results, we discuss first clues about the role played by silicon on slowing down the UMo/Al interaction process.