Several irradiation experiments of U(Mo) dispersion fuel performed with aluminum as matrix resulted in unacceptable swelling of the fuel plate due to the formation of an interaction layer between Al and U(Mo). An improvement in fuel behavior can be achieved by adding Si to the Al matrix and creating a Si rich preformed layer which delays the formation of the inter action layer. Such Al–Si matrices can be formed either by mixing silicon powder with aluminum or using an AlSi alloy. Aging experiments on AlSi alloys reveal that giving the alloy the correct heat treatment results in a homogenous dispersion of fine Si precipitates in a soft and strain free Al matrix. The diffusion of such small precipitates towards the U(Mo) particles will be more effective than the transportation of Si from the larger Si particles used in a mixture matrix. Out of pile experiments are performed to show the difference between using a mixture or an alloy for the interaction with U(Mo). It was found that the U(Mo) particles dispersed in an AlSi alloy matrix have a more uniform Si rich preformed layer after heat treatment .