This study deals with the durability of immobilization matrices, drawing comparisons among the release characteristics of cementitious mortars with or without silica fume, before and after freezing-thawing cycles. Three different dosages of silica fume have been experimented, using silica fume as a substitute of cement. The results obtained from the leaching tests have emphasized, in all the matrices which had undergone the freeze-thaw cycles, an increase of the percentage of tracer released with respect to the same matrices before the freezing-thawing cycles. As a consequence of the freezing-thawing cycles, the velocity of release has also increased in all the experimented matrices. However, the tests have reconfirmed the positive effect of the addition of silica fume.