  This high level liquid radioactive reprocessing waste will become vitrified
in order to obtain a stable borosilicate waste glass matrix that provides
protection against environmental dispersion. Since vitrified waste is in a
solid form, transportation, storage and final geological disposal are
facilitated. The glass products contain the non-extracted fraction of uranium
and plutonium together with the minor actinides Am, Np and Cm and fission
products such as (90Sr, 99Tc ou 137Cs). In the long term, the safest way to
deal with actinide containing nuclear waste (vitrified waste or spent fuel) is
geological disposal. The disposal locations are isolated from biosphere by
engineered barriers while dense rock characteristics and low groundwater flow
assure that any potential return of radionuclides to biosphere by groundwater
transport will be retarded for many hundreds of thousands of years. If the
actinides (and other radionuclides) are conditioned within a glass matrix and
cast into metal canisters, actinides can only be released to the ground water
if the canister and the glass matrix becomes dissolved or corroded and this
alteration process will take many hundreds of thousands of years. Even if the
glass finally becomes dissolved or corroded entirely in ground water, large
quantities of actinides will in all likelihood remain immobile by being bound
to secondary phases, which form as solid corrosion products on the glass
surface during the alteration process. Typical glass corrosion products are gel
like and crystalline phases such as silicates and oxy-hydroxides.To predict the
performance of the actinide containing waste glass, one needs to understand the
dissolution process of the glass matrix, the thermodynamic and kinetic
constraints which lead to actinide fixation in secondary reaction products as
well as the short and long term transport processes.
