The Belgian Reactor 1 (BR1) fuel is composed of natural unalloyed metallic uranium, coated with an aluminosilicate alloy bonding layer and an U(Al,Si)3 anti-diffusion layer, and encapsulated in an aluminium container. One solution for the long-term management of this fuel, which will eventually become waste, is geological disposal. To do so, a direct embedding of the waste in a cement-based material could be used. In contact with the highly alkaline cement pore water, high corrosion rates are observed for aluminium and uranium to form e.g. aluminium hydroxide, uranium oxides and hydrides, and hydrogen gas. These products can then lead to stresses in the encapsulated matrix, damaging this matrix. However, if a cement-based material possessing a low porosity is used, the diffusion of water through the material will be limited, and due to this mass transport limitation, the corrosion rate should drastically decrease.