Nuclear fuel is made by UO2 enrichment in U235 (3 ? 5 %), the fission of U235 modified
the chemical composition, generating fission product, actinides and activation
products.Also, it is observed microstructural modifications like defects, bubbles, cracks
and segregation of metallic and ceramic phases. Spent nuclear Fuel ?SF? has γ, β and α
emisors, the total activity will depend on their irradiation history, burn - up and cooling
time (Astudillo Pastor, 2001; Quiñones et al., 2003). Any environmental assessment of SF
disposal requires a prediction of the radionuclides release from SF matrix when its matrix
will be in contact with groundwater (Corbel et al., 2006).